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diff --git a/Documentation/virt/index.rst b/Documentation/virt/index.rst new file mode 100644 index 000000000000..062ffb527043 --- /dev/null +++ b/Documentation/virt/index.rst @@ -0,0 +1,18 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================ +Linux Virtualization Support +============================ + +.. toctree:: + :maxdepth: 2 + + kvm/index + paravirt_ops + +.. only:: html and subproject + + Indices + ======= + + * :ref:`genindex` diff --git a/Documentation/virt/kvm/amd-memory-encryption.rst b/Documentation/virt/kvm/amd-memory-encryption.rst new file mode 100644 index 000000000000..d18c97b4e140 --- /dev/null +++ b/Documentation/virt/kvm/amd-memory-encryption.rst @@ -0,0 +1,250 @@ +====================================== +Secure Encrypted Virtualization (SEV) +====================================== + +Overview +======== + +Secure Encrypted Virtualization (SEV) is a feature found on AMD processors. + +SEV is an extension to the AMD-V architecture which supports running +virtual machines (VMs) under the control of a hypervisor. When enabled, +the memory contents of a VM will be transparently encrypted with a key +unique to that VM. + +The hypervisor can determine the SEV support through the CPUID +instruction. The CPUID function 0x8000001f reports information related +to SEV:: + + 0x8000001f[eax]: + Bit[1] indicates support for SEV + ... + [ecx]: + Bits[31:0] Number of encrypted guests supported simultaneously + +If support for SEV is present, MSR 0xc001_0010 (MSR_K8_SYSCFG) and MSR 0xc001_0015 +(MSR_K7_HWCR) can be used to determine if it can be enabled:: + + 0xc001_0010: + Bit[23] 1 = memory encryption can be enabled + 0 = memory encryption can not be enabled + + 0xc001_0015: + Bit[0] 1 = memory encryption can be enabled + 0 = memory encryption can not be enabled + +When SEV support is available, it can be enabled in a specific VM by +setting the SEV bit before executing VMRUN.:: + + VMCB[0x90]: + Bit[1] 1 = SEV is enabled + 0 = SEV is disabled + +SEV hardware uses ASIDs to associate a memory encryption key with a VM. +Hence, the ASID for the SEV-enabled guests must be from 1 to a maximum value +defined in the CPUID 0x8000001f[ecx] field. + +SEV Key Management +================== + +The SEV guest key management is handled by a separate processor called the AMD +Secure Processor (AMD-SP). Firmware running inside the AMD-SP provides a secure +key management interface to perform common hypervisor activities such as +encrypting bootstrap code, snapshot, migrating and debugging the guest. For more +information, see the SEV Key Management spec [api-spec]_ + +KVM implements the following commands to support common lifecycle events of SEV +guests, such as launching, running, snapshotting, migrating and decommissioning. + +1. KVM_SEV_INIT +--------------- + +The KVM_SEV_INIT command is used by the hypervisor to initialize the SEV platform +context. In a typical workflow, this command should be the first command issued. + +Returns: 0 on success, -negative on error + +2. KVM_SEV_LAUNCH_START +----------------------- + +The KVM_SEV_LAUNCH_START command is used for creating the memory encryption +context. To create the encryption context, user must provide a guest policy, +the owner's public Diffie-Hellman (PDH) key and session information. + +Parameters: struct kvm_sev_launch_start (in/out) + +Returns: 0 on success, -negative on error + +:: + + struct kvm_sev_launch_start { + __u32 handle; /* if zero then firmware creates a new handle */ + __u32 policy; /* guest's policy */ + + __u64 dh_uaddr; /* userspace address pointing to the guest owner's PDH key */ + __u32 dh_len; + + __u64 session_addr; /* userspace address which points to the guest session information */ + __u32 session_len; + }; + +On success, the 'handle' field contains a new handle and on error, a negative value. + +For more details, see SEV spec Section 6.2. + +3. KVM_SEV_LAUNCH_UPDATE_DATA +----------------------------- + +The KVM_SEV_LAUNCH_UPDATE_DATA is used for encrypting a memory region. It also +calculates a measurement of the memory contents. The measurement is a signature +of the memory contents that can be sent to the guest owner as an attestation +that the memory was encrypted correctly by the firmware. + +Parameters (in): struct kvm_sev_launch_update_data + +Returns: 0 on success, -negative on error + +:: + + struct kvm_sev_launch_update { + __u64 uaddr; /* userspace address to be encrypted (must be 16-byte aligned) */ + __u32 len; /* length of the data to be encrypted (must be 16-byte aligned) */ + }; + +For more details, see SEV spec Section 6.3. + +4. KVM_SEV_LAUNCH_MEASURE +------------------------- + +The KVM_SEV_LAUNCH_MEASURE command is used to retrieve the measurement of the +data encrypted by the KVM_SEV_LAUNCH_UPDATE_DATA command. The guest owner may +wait to provide the guest with confidential information until it can verify the +measurement. Since the guest owner knows the initial contents of the guest at +boot, the measurement can be verified by comparing it to what the guest owner +expects. + +Parameters (in): struct kvm_sev_launch_measure + +Returns: 0 on success, -negative on error + +:: + + struct kvm_sev_launch_measure { + __u64 uaddr; /* where to copy the measurement */ + __u32 len; /* length of measurement blob */ + }; + +For more details on the measurement verification flow, see SEV spec Section 6.4. + +5. KVM_SEV_LAUNCH_FINISH +------------------------ + +After completion of the launch flow, the KVM_SEV_LAUNCH_FINISH command can be +issued to make the guest ready for the execution. + +Returns: 0 on success, -negative on error + +6. KVM_SEV_GUEST_STATUS +----------------------- + +The KVM_SEV_GUEST_STATUS command is used to retrieve status information about a +SEV-enabled guest. + +Parameters (out): struct kvm_sev_guest_status + +Returns: 0 on success, -negative on error + +:: + + struct kvm_sev_guest_status { + __u32 handle; /* guest handle */ + __u32 policy; /* guest policy */ + __u8 state; /* guest state (see enum below) */ + }; + +SEV guest state: + +:: + + enum { + SEV_STATE_INVALID = 0; + SEV_STATE_LAUNCHING, /* guest is currently being launched */ + SEV_STATE_SECRET, /* guest is being launched and ready to accept the ciphertext data */ + SEV_STATE_RUNNING, /* guest is fully launched and running */ + SEV_STATE_RECEIVING, /* guest is being migrated in from another SEV machine */ + SEV_STATE_SENDING /* guest is getting migrated out to another SEV machine */ + }; + +7. KVM_SEV_DBG_DECRYPT +---------------------- + +The KVM_SEV_DEBUG_DECRYPT command can be used by the hypervisor to request the +firmware to decrypt the data at the given memory region. + +Parameters (in): struct kvm_sev_dbg + +Returns: 0 on success, -negative on error + +:: + + struct kvm_sev_dbg { + __u64 src_uaddr; /* userspace address of data to decrypt */ + __u64 dst_uaddr; /* userspace address of destination */ + __u32 len; /* length of memory region to decrypt */ + }; + +The command returns an error if the guest policy does not allow debugging. + +8. KVM_SEV_DBG_ENCRYPT +---------------------- + +The KVM_SEV_DEBUG_ENCRYPT command can be used by the hypervisor to request the +firmware to encrypt the data at the given memory region. + +Parameters (in): struct kvm_sev_dbg + +Returns: 0 on success, -negative on error + +:: + + struct kvm_sev_dbg { + __u64 src_uaddr; /* userspace address of data to encrypt */ + __u64 dst_uaddr; /* userspace address of destination */ + __u32 len; /* length of memory region to encrypt */ + }; + +The command returns an error if the guest policy does not allow debugging. + +9. KVM_SEV_LAUNCH_SECRET +------------------------ + +The KVM_SEV_LAUNCH_SECRET command can be used by the hypervisor to inject secret +data after the measurement has been validated by the guest owner. + +Parameters (in): struct kvm_sev_launch_secret + +Returns: 0 on success, -negative on error + +:: + + struct kvm_sev_launch_secret { + __u64 hdr_uaddr; /* userspace address containing the packet header */ + __u32 hdr_len; + + __u64 guest_uaddr; /* the guest memory region where the secret should be injected */ + __u32 guest_len; + + __u64 trans_uaddr; /* the hypervisor memory region which contains the secret */ + __u32 trans_len; + }; + +References +========== + + +See [white-paper]_, [api-spec]_, [amd-apm]_ and [kvm-forum]_ for more info. + +.. [white-paper] http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/12/AMD_Memory_Encryption_Whitepaper_v7-Public.pdf +.. [api-spec] http://support.amd.com/TechDocs/55766_SEV-KM_API_Specification.pdf +.. [amd-apm] http://support.amd.com/TechDocs/24593.pdf (section 15.34) +.. [kvm-forum] http://www.linux-kvm.org/images/7/74/02x08A-Thomas_Lendacky-AMDs_Virtualizatoin_Memory_Encryption_Technology.pdf diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt new file mode 100644 index 000000000000..2d067767b617 --- /dev/null +++ b/Documentation/virt/kvm/api.txt @@ -0,0 +1,5296 @@ +The Definitive KVM (Kernel-based Virtual Machine) API Documentation +=================================================================== + +1. General description +---------------------- + +The kvm API is a set of ioctls that are issued to control various aspects +of a virtual machine. The ioctls belong to three classes: + + - System ioctls: These query and set global attributes which affect the + whole kvm subsystem. In addition a system ioctl is used to create + virtual machines. + + - VM ioctls: These query and set attributes that affect an entire virtual + machine, for example memory layout. In addition a VM ioctl is used to + create virtual cpus (vcpus) and devices. + + VM ioctls must be issued from the same process (address space) that was + used to create the VM. + + - vcpu ioctls: These query and set attributes that control the operation + of a single virtual cpu. + + vcpu ioctls should be issued from the same thread that was used to create + the vcpu, except for asynchronous vcpu ioctl that are marked as such in + the documentation. Otherwise, the first ioctl after switching threads + could see a performance impact. + + - device ioctls: These query and set attributes that control the operation + of a single device. + + device ioctls must be issued from the same process (address space) that + was used to create the VM. + +2. File descriptors +------------------- + +The kvm API is centered around file descriptors. An initial +open("/dev/kvm") obtains a handle to the kvm subsystem; this handle +can be used to issue system ioctls. A KVM_CREATE_VM ioctl on this +handle will create a VM file descriptor which can be used to issue VM +ioctls. A KVM_CREATE_VCPU or KVM_CREATE_DEVICE ioctl on a VM fd will +create a virtual cpu or device and return a file descriptor pointing to +the new resource. Finally, ioctls on a vcpu or device fd can be used +to control the vcpu or device. For vcpus, this includes the important +task of actually running guest code. + +In general file descriptors can be migrated among processes by means +of fork() and the SCM_RIGHTS facility of unix domain socket. These +kinds of tricks are explicitly not supported by kvm. While they will +not cause harm to the host, their actual behavior is not guaranteed by +the API. See "General description" for details on the ioctl usage +model that is supported by KVM. + +It is important to note that althought VM ioctls may only be issued from +the process that created the VM, a VM's lifecycle is associated with its +file descriptor, not its creator (process). In other words, the VM and +its resources, *including the associated address space*, are not freed +until the last reference to the VM's file descriptor has been released. +For example, if fork() is issued after ioctl(KVM_CREATE_VM), the VM will +not be freed until both the parent (original) process and its child have +put their references to the VM's file descriptor. + +Because a VM's resources are not freed until the last reference to its +file descriptor is released, creating additional references to a VM via +via fork(), dup(), etc... without careful consideration is strongly +discouraged and may have unwanted side effects, e.g. memory allocated +by and on behalf of the VM's process may not be freed/unaccounted when +the VM is shut down. + + +3. Extensions +------------- + +As of Linux 2.6.22, the KVM ABI has been stabilized: no backward +incompatible change are allowed. However, there is an extension +facility that allows backward-compatible extensions to the API to be +queried and used. + +The extension mechanism is not based on the Linux version number. +Instead, kvm defines extension identifiers and a facility to query +whether a particular extension identifier is available. If it is, a +set of ioctls is available for application use. + + +4. API description +------------------ + +This section describes ioctls that can be used to control kvm guests. +For each ioctl, the following information is provided along with a +description: + + Capability: which KVM extension provides this ioctl. Can be 'basic', + which means that is will be provided by any kernel that supports + API version 12 (see section 4.1), a KVM_CAP_xyz constant, which + means availability needs to be checked with KVM_CHECK_EXTENSION + (see section 4.4), or 'none' which means that while not all kernels + support this ioctl, there's no capability bit to check its + availability: for kernels that don't support the ioctl, + the ioctl returns -ENOTTY. + + Architectures: which instruction set architectures provide this ioctl. + x86 includes both i386 and x86_64. + + Type: system, vm, or vcpu. + + Parameters: what parameters are accepted by the ioctl. + + Returns: the return value. General error numbers (EBADF, ENOMEM, EINVAL) + are not detailed, but errors with specific meanings are. + + +4.1 KVM_GET_API_VERSION + +Capability: basic +Architectures: all +Type: system ioctl +Parameters: none +Returns: the constant KVM_API_VERSION (=12) + +This identifies the API version as the stable kvm API. It is not +expected that this number will change. However, Linux 2.6.20 and +2.6.21 report earlier versions; these are not documented and not +supported. Applications should refuse to run if KVM_GET_API_VERSION +returns a value other than 12. If this check passes, all ioctls +described as 'basic' will be available. + + +4.2 KVM_CREATE_VM + +Capability: basic +Architectures: all +Type: system ioctl +Parameters: machine type identifier (KVM_VM_*) +Returns: a VM fd that can be used to control the new virtual machine. + +The new VM has no virtual cpus and no memory. +You probably want to use 0 as machine type. + +In order to create user controlled virtual machines on S390, check +KVM_CAP_S390_UCONTROL and use the flag KVM_VM_S390_UCONTROL as +privileged user (CAP_SYS_ADMIN). + +To use hardware assisted virtualization on MIPS (VZ ASE) rather than +the default trap & emulate implementation (which changes the virtual +memory layout to fit in user mode), check KVM_CAP_MIPS_VZ and use the +flag KVM_VM_MIPS_VZ. + + +On arm64, the physical address size for a VM (IPA Size limit) is limited +to 40bits by default. The limit can be configured if the host supports the +extension KVM_CAP_ARM_VM_IPA_SIZE. When supported, use +KVM_VM_TYPE_ARM_IPA_SIZE(IPA_Bits) to set the size in the machine type +identifier, where IPA_Bits is the maximum width of any physical +address used by the VM. The IPA_Bits is encoded in bits[7-0] of the +machine type identifier. + +e.g, to configure a guest to use 48bit physical address size : + + vm_fd = ioctl(dev_fd, KVM_CREATE_VM, KVM_VM_TYPE_ARM_IPA_SIZE(48)); + +The requested size (IPA_Bits) must be : + 0 - Implies default size, 40bits (for backward compatibility) + + or + + N - Implies N bits, where N is a positive integer such that, + 32 <= N <= Host_IPA_Limit + +Host_IPA_Limit is the maximum possible value for IPA_Bits on the host and +is dependent on the CPU capability and the kernel configuration. The limit can +be retrieved using KVM_CAP_ARM_VM_IPA_SIZE of the KVM_CHECK_EXTENSION +ioctl() at run-time. + +Please note that configuring the IPA size does not affect the capability +exposed by the guest CPUs in ID_AA64MMFR0_EL1[PARange]. It only affects +size of the address translated by the stage2 level (guest physical to +host physical address translations). + + +4.3 KVM_GET_MSR_INDEX_LIST, KVM_GET_MSR_FEATURE_INDEX_LIST + +Capability: basic, KVM_CAP_GET_MSR_FEATURES for KVM_GET_MSR_FEATURE_INDEX_LIST +Architectures: x86 +Type: system ioctl +Parameters: struct kvm_msr_list (in/out) +Returns: 0 on success; -1 on error +Errors: + EFAULT: the msr index list cannot be read from or written to + E2BIG: the msr index list is to be to fit in the array specified by + the user. + +struct kvm_msr_list { + __u32 nmsrs; /* number of msrs in entries */ + __u32 indices[0]; +}; + +The user fills in the size of the indices array in nmsrs, and in return +kvm adjusts nmsrs to reflect the actual number of msrs and fills in the +indices array with their numbers. + +KVM_GET_MSR_INDEX_LIST returns the guest msrs that are supported. The list +varies by kvm version and host processor, but does not change otherwise. + +Note: if kvm indicates supports MCE (KVM_CAP_MCE), then the MCE bank MSRs are +not returned in the MSR list, as different vcpus can have a different number +of banks, as set via the KVM_X86_SETUP_MCE ioctl. + +KVM_GET_MSR_FEATURE_INDEX_LIST returns the list of MSRs that can be passed +to the KVM_GET_MSRS system ioctl. This lets userspace probe host capabilities +and processor features that are exposed via MSRs (e.g., VMX capabilities). +This list also varies by kvm version and host processor, but does not change +otherwise. + + +4.4 KVM_CHECK_EXTENSION + +Capability: basic, KVM_CAP_CHECK_EXTENSION_VM for vm ioctl +Architectures: all +Type: system ioctl, vm ioctl +Parameters: extension identifier (KVM_CAP_*) +Returns: 0 if unsupported; 1 (or some other positive integer) if supported + +The API allows the application to query about extensions to the core +kvm API. Userspace passes an extension identifier (an integer) and +receives an integer that describes the extension availability. +Generally 0 means no and 1 means yes, but some extensions may report +additional information in the integer return value. + +Based on their initialization different VMs may have different capabilities. +It is thus encouraged to use the vm ioctl to query for capabilities (available +with KVM_CAP_CHECK_EXTENSION_VM on the vm fd) + +4.5 KVM_GET_VCPU_MMAP_SIZE + +Capability: basic +Architectures: all +Type: system ioctl +Parameters: none +Returns: size of vcpu mmap area, in bytes + +The KVM_RUN ioctl (cf.) communicates with userspace via a shared +memory region. This ioctl returns the size of that region. See the +KVM_RUN documentation for details. + + +4.6 KVM_SET_MEMORY_REGION + +Capability: basic +Architectures: all +Type: vm ioctl +Parameters: struct kvm_memory_region (in) +Returns: 0 on success, -1 on error + +This ioctl is obsolete and has been removed. + + +4.7 KVM_CREATE_VCPU + +Capability: basic +Architectures: all +Type: vm ioctl +Parameters: vcpu id (apic id on x86) +Returns: vcpu fd on success, -1 on error + +This API adds a vcpu to a virtual machine. No more than max_vcpus may be added. +The vcpu id is an integer in the range [0, max_vcpu_id). + +The recommended max_vcpus value can be retrieved using the KVM_CAP_NR_VCPUS of +the KVM_CHECK_EXTENSION ioctl() at run-time. +The maximum possible value for max_vcpus can be retrieved using the +KVM_CAP_MAX_VCPUS of the KVM_CHECK_EXTENSION ioctl() at run-time. + +If the KVM_CAP_NR_VCPUS does not exist, you should assume that max_vcpus is 4 +cpus max. +If the KVM_CAP_MAX_VCPUS does not exist, you should assume that max_vcpus is +same as the value returned from KVM_CAP_NR_VCPUS. + +The maximum possible value for max_vcpu_id can be retrieved using the +KVM_CAP_MAX_VCPU_ID of the KVM_CHECK_EXTENSION ioctl() at run-time. + +If the KVM_CAP_MAX_VCPU_ID does not exist, you should assume that max_vcpu_id +is the same as the value returned from KVM_CAP_MAX_VCPUS. + +On powerpc using book3s_hv mode, the vcpus are mapped onto virtual +threads in one or more virtual CPU cores. (This is because the +hardware requires all the hardware threads in a CPU core to be in the +same partition.) The KVM_CAP_PPC_SMT capability indicates the number +of vcpus per virtual core (vcore). The vcore id is obtained by +dividing the vcpu id by the number of vcpus per vcore. The vcpus in a +given vcore will always be in the same physical core as each other +(though that might be a different physical core from time to time). +Userspace can control the threading (SMT) mode of the guest by its +allocation of vcpu ids. For example, if userspace wants +single-threaded guest vcpus, it should make all vcpu ids be a multiple +of the number of vcpus per vcore. + +For virtual cpus that have been created with S390 user controlled virtual +machines, the resulting vcpu fd can be memory mapped at page offset +KVM_S390_SIE_PAGE_OFFSET in order to obtain a memory map of the virtual +cpu's hardware control block. + + +4.8 KVM_GET_DIRTY_LOG (vm ioctl) + +Capability: basic +Architectures: all +Type: vm ioctl +Parameters: struct kvm_dirty_log (in/out) +Returns: 0 on success, -1 on error + +/* for KVM_GET_DIRTY_LOG */ +struct kvm_dirty_log { + __u32 slot; + __u32 padding; + union { + void __user *dirty_bitmap; /* one bit per page */ + __u64 padding; + }; +}; + +Given a memory slot, return a bitmap containing any pages dirtied +since the last call to this ioctl. Bit 0 is the first page in the +memory slot. Ensure the entire structure is cleared to avoid padding +issues. + +If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 specifies +the address space for which you want to return the dirty bitmap. +They must be less than the value that KVM_CHECK_EXTENSION returns for +the KVM_CAP_MULTI_ADDRESS_SPACE capability. + +The bits in the dirty bitmap are cleared before the ioctl returns, unless +KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is enabled. For more information, +see the description of the capability. + +4.9 KVM_SET_MEMORY_ALIAS + +Capability: basic +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_memory_alias (in) +Returns: 0 (success), -1 (error) + +This ioctl is obsolete and has been removed. + + +4.10 KVM_RUN + +Capability: basic +Architectures: all +Type: vcpu ioctl +Parameters: none +Returns: 0 on success, -1 on error +Errors: + EINTR: an unmasked signal is pending + +This ioctl is used to run a guest virtual cpu. While there are no +explicit parameters, there is an implicit parameter block that can be +obtained by mmap()ing the vcpu fd at offset 0, with the size given by +KVM_GET_VCPU_MMAP_SIZE. The parameter block is formatted as a 'struct +kvm_run' (see below). + + +4.11 KVM_GET_REGS + +Capability: basic +Architectures: all except ARM, arm64 +Type: vcpu ioctl +Parameters: struct kvm_regs (out) +Returns: 0 on success, -1 on error + +Reads the general purpose registers from the vcpu. + +/* x86 */ +struct kvm_regs { + /* out (KVM_GET_REGS) / in (KVM_SET_REGS) */ + __u64 rax, rbx, rcx, rdx; + __u64 rsi, rdi, rsp, rbp; + __u64 r8, r9, r10, r11; + __u64 r12, r13, r14, r15; + __u64 rip, rflags; +}; + +/* mips */ +struct kvm_regs { + /* out (KVM_GET_REGS) / in (KVM_SET_REGS) */ + __u64 gpr[32]; + __u64 hi; + __u64 lo; + __u64 pc; +}; + + +4.12 KVM_SET_REGS + +Capability: basic +Architectures: all except ARM, arm64 +Type: vcpu ioctl +Parameters: struct kvm_regs (in) +Returns: 0 on success, -1 on error + +Writes the general purpose registers into the vcpu. + +See KVM_GET_REGS for the data structure. + + +4.13 KVM_GET_SREGS + +Capability: basic +Architectures: x86, ppc +Type: vcpu ioctl +Parameters: struct kvm_sregs (out) +Returns: 0 on success, -1 on error + +Reads special registers from the vcpu. + +/* x86 */ +struct kvm_sregs { + struct kvm_segment cs, ds, es, fs, gs, ss; + struct kvm_segment tr, ldt; + struct kvm_dtable gdt, idt; + __u64 cr0, cr2, cr3, cr4, cr8; + __u64 efer; + __u64 apic_base; + __u64 interrupt_bitmap[(KVM_NR_INTERRUPTS + 63) / 64]; +}; + +/* ppc -- see arch/powerpc/include/uapi/asm/kvm.h */ + +interrupt_bitmap is a bitmap of pending external interrupts. At most +one bit may be set. This interrupt has been acknowledged by the APIC +but not yet injected into the cpu core. + + +4.14 KVM_SET_SREGS + +Capability: basic +Architectures: x86, ppc +Type: vcpu ioctl +Parameters: struct kvm_sregs (in) +Returns: 0 on success, -1 on error + +Writes special registers into the vcpu. See KVM_GET_SREGS for the +data structures. + + +4.15 KVM_TRANSLATE + +Capability: basic +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_translation (in/out) +Returns: 0 on success, -1 on error + +Translates a virtual address according to the vcpu's current address +translation mode. + +struct kvm_translation { + /* in */ + __u64 linear_address; + + /* out */ + __u64 physical_address; + __u8 valid; + __u8 writeable; + __u8 usermode; + __u8 pad[5]; +}; + + +4.16 KVM_INTERRUPT + +Capability: basic +Architectures: x86, ppc, mips +Type: vcpu ioctl +Parameters: struct kvm_interrupt (in) +Returns: 0 on success, negative on failure. + +Queues a hardware interrupt vector to be injected. + +/* for KVM_INTERRUPT */ +struct kvm_interrupt { + /* in */ + __u32 irq; +}; + +X86: + +Returns: 0 on success, + -EEXIST if an interrupt is already enqueued + -EINVAL the the irq number is invalid + -ENXIO if the PIC is in the kernel + -EFAULT if the pointer is invalid + +Note 'irq' is an interrupt vector, not an interrupt pin or line. This +ioctl is useful if the in-kernel PIC is not used. + +PPC: + +Queues an external interrupt to be injected. This ioctl is overleaded +with 3 different irq values: + +a) KVM_INTERRUPT_SET + + This injects an edge type external interrupt into the guest once it's ready + to receive interrupts. When injected, the interrupt is done. + +b) KVM_INTERRUPT_UNSET + + This unsets any pending interrupt. + + Only available with KVM_CAP_PPC_UNSET_IRQ. + +c) KVM_INTERRUPT_SET_LEVEL + + This injects a level type external interrupt into the guest context. The + interrupt stays pending until a specific ioctl with KVM_INTERRUPT_UNSET + is triggered. + + Only available with KVM_CAP_PPC_IRQ_LEVEL. + +Note that any value for 'irq' other than the ones stated above is invalid +and incurs unexpected behavior. + +This is an asynchronous vcpu ioctl and can be invoked from any thread. + +MIPS: + +Queues an external interrupt to be injected into the virtual CPU. A negative +interrupt number dequeues the interrupt. + +This is an asynchronous vcpu ioctl and can be invoked from any thread. + + +4.17 KVM_DEBUG_GUEST + +Capability: basic +Architectures: none +Type: vcpu ioctl +Parameters: none) +Returns: -1 on error + +Support for this has been removed. Use KVM_SET_GUEST_DEBUG instead. + + +4.18 KVM_GET_MSRS + +Capability: basic (vcpu), KVM_CAP_GET_MSR_FEATURES (system) +Architectures: x86 +Type: system ioctl, vcpu ioctl +Parameters: struct kvm_msrs (in/out) +Returns: number of msrs successfully returned; + -1 on error + +When used as a system ioctl: +Reads the values of MSR-based features that are available for the VM. This +is similar to KVM_GET_SUPPORTED_CPUID, but it returns MSR indices and values. +The list of msr-based features can be obtained using KVM_GET_MSR_FEATURE_INDEX_LIST +in a system ioctl. + +When used as a vcpu ioctl: +Reads model-specific registers from the vcpu. Supported msr indices can +be obtained using KVM_GET_MSR_INDEX_LIST in a system ioctl. + +struct kvm_msrs { + __u32 nmsrs; /* number of msrs in entries */ + __u32 pad; + + struct kvm_msr_entry entries[0]; +}; + +struct kvm_msr_entry { + __u32 index; + __u32 reserved; + __u64 data; +}; + +Application code should set the 'nmsrs' member (which indicates the +size of the entries array) and the 'index' member of each array entry. +kvm will fill in the 'data' member. + + +4.19 KVM_SET_MSRS + +Capability: basic +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_msrs (in) +Returns: 0 on success, -1 on error + +Writes model-specific registers to the vcpu. See KVM_GET_MSRS for the +data structures. + +Application code should set the 'nmsrs' member (which indicates the +size of the entries array), and the 'index' and 'data' members of each +array entry. + + +4.20 KVM_SET_CPUID + +Capability: basic +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_cpuid (in) +Returns: 0 on success, -1 on error + +Defines the vcpu responses to the cpuid instruction. Applications +should use the KVM_SET_CPUID2 ioctl if available. + + +struct kvm_cpuid_entry { + __u32 function; + __u32 eax; + __u32 ebx; + __u32 ecx; + __u32 edx; + __u32 padding; +}; + +/* for KVM_SET_CPUID */ +struct kvm_cpuid { + __u32 nent; + __u32 padding; + struct kvm_cpuid_entry entries[0]; +}; + + +4.21 KVM_SET_SIGNAL_MASK + +Capability: basic +Architectures: all +Type: vcpu ioctl +Parameters: struct kvm_signal_mask (in) +Returns: 0 on success, -1 on error + +Defines which signals are blocked during execution of KVM_RUN. This +signal mask temporarily overrides the threads signal mask. Any +unblocked signal received (except SIGKILL and SIGSTOP, which retain +their traditional behaviour) will cause KVM_RUN to return with -EINTR. + +Note the signal will only be delivered if not blocked by the original +signal mask. + +/* for KVM_SET_SIGNAL_MASK */ +struct kvm_signal_mask { + __u32 len; + __u8 sigset[0]; +}; + + +4.22 KVM_GET_FPU + +Capability: basic +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_fpu (out) +Returns: 0 on success, -1 on error + +Reads the floating point state from the vcpu. + +/* for KVM_GET_FPU and KVM_SET_FPU */ +struct kvm_fpu { + __u8 fpr[8][16]; + __u16 fcw; + __u16 fsw; + __u8 ftwx; /* in fxsave format */ + __u8 pad1; + __u16 last_opcode; + __u64 last_ip; + __u64 last_dp; + __u8 xmm[16][16]; + __u32 mxcsr; + __u32 pad2; +}; + + +4.23 KVM_SET_FPU + +Capability: basic +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_fpu (in) +Returns: 0 on success, -1 on error + +Writes the floating point state to the vcpu. + +/* for KVM_GET_FPU and KVM_SET_FPU */ +struct kvm_fpu { + __u8 fpr[8][16]; + __u16 fcw; + __u16 fsw; + __u8 ftwx; /* in fxsave format */ + __u8 pad1; + __u16 last_opcode; + __u64 last_ip; + __u64 last_dp; + __u8 xmm[16][16]; + __u32 mxcsr; + __u32 pad2; +}; + + +4.24 KVM_CREATE_IRQCHIP + +Capability: KVM_CAP_IRQCHIP, KVM_CAP_S390_IRQCHIP (s390) +Architectures: x86, ARM, arm64, s390 +Type: vm ioctl +Parameters: none +Returns: 0 on success, -1 on error + +Creates an interrupt controller model in the kernel. +On x86, creates a virtual ioapic, a virtual PIC (two PICs, nested), and sets up +future vcpus to have a local APIC. IRQ routing for GSIs 0-15 is set to both +PIC and IOAPIC; GSI 16-23 only go to the IOAPIC. +On ARM/arm64, a GICv2 is created. Any other GIC versions require the usage of +KVM_CREATE_DEVICE, which also supports creating a GICv2. Using +KVM_CREATE_DEVICE is preferred over KVM_CREATE_IRQCHIP for GICv2. +On s390, a dummy irq routing table is created. + +Note that on s390 the KVM_CAP_S390_IRQCHIP vm capability needs to be enabled +before KVM_CREATE_IRQCHIP can be used. + + +4.25 KVM_IRQ_LINE + +Capability: KVM_CAP_IRQCHIP +Architectures: x86, arm, arm64 +Type: vm ioctl +Parameters: struct kvm_irq_level +Returns: 0 on success, -1 on error + +Sets the level of a GSI input to the interrupt controller model in the kernel. +On some architectures it is required that an interrupt controller model has +been previously created with KVM_CREATE_IRQCHIP. Note that edge-triggered +interrupts require the level to be set to 1 and then back to 0. + +On real hardware, interrupt pins can be active-low or active-high. This +does not matter for the level field of struct kvm_irq_level: 1 always +means active (asserted), 0 means inactive (deasserted). + +x86 allows the operating system to program the interrupt polarity +(active-low/active-high) for level-triggered interrupts, and KVM used +to consider the polarity. However, due to bitrot in the handling of +active-low interrupts, the above convention is now valid on x86 too. +This is signaled by KVM_CAP_X86_IOAPIC_POLARITY_IGNORED. Userspace +should not present interrupts to the guest as active-low unless this +capability is present (or unless it is not using the in-kernel irqchip, +of course). + + +ARM/arm64 can signal an interrupt either at the CPU level, or at the +in-kernel irqchip (GIC), and for in-kernel irqchip can tell the GIC to +use PPIs designated for specific cpus. The irq field is interpreted +like this: + + Â bits: | 31 ... 24 | 23 ... 16 | 15 ... 0 | + field: | irq_type | vcpu_index | irq_id | + +The irq_type field has the following values: +- irq_type[0]: out-of-kernel GIC: irq_id 0 is IRQ, irq_id 1 is FIQ +- irq_type[1]: in-kernel GIC: SPI, irq_id between 32 and 1019 (incl.) + (the vcpu_index field is ignored) +- irq_type[2]: in-kernel GIC: PPI, irq_id between 16 and 31 (incl.) + +(The irq_id field thus corresponds nicely to the IRQ ID in the ARM GIC specs) + +In both cases, level is used to assert/deassert the line. + +struct kvm_irq_level { + union { + __u32 irq; /* GSI */ + __s32 status; /* not used for KVM_IRQ_LEVEL */ + }; + __u32 level; /* 0 or 1 */ +}; + + +4.26 KVM_GET_IRQCHIP + +Capability: KVM_CAP_IRQCHIP +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_irqchip (in/out) +Returns: 0 on success, -1 on error + +Reads the state of a kernel interrupt controller created with +KVM_CREATE_IRQCHIP into a buffer provided by the caller. + +struct kvm_irqchip { + __u32 chip_id; /* 0 = PIC1, 1 = PIC2, 2 = IOAPIC */ + __u32 pad; + union { + char dummy[512]; /* reserving space */ + struct kvm_pic_state pic; + struct kvm_ioapic_state ioapic; + } chip; +}; + + +4.27 KVM_SET_IRQCHIP + +Capability: KVM_CAP_IRQCHIP +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_irqchip (in) +Returns: 0 on success, -1 on error + +Sets the state of a kernel interrupt controller created with +KVM_CREATE_IRQCHIP from a buffer provided by the caller. + +struct kvm_irqchip { + __u32 chip_id; /* 0 = PIC1, 1 = PIC2, 2 = IOAPIC */ + __u32 pad; + union { + char dummy[512]; /* reserving space */ + struct kvm_pic_state pic; + struct kvm_ioapic_state ioapic; + } chip; +}; + + +4.28 KVM_XEN_HVM_CONFIG + +Capability: KVM_CAP_XEN_HVM +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_xen_hvm_config (in) +Returns: 0 on success, -1 on error + +Sets the MSR that the Xen HVM guest uses to initialize its hypercall +page, and provides the starting address and size of the hypercall +blobs in userspace. When the guest writes the MSR, kvm copies one +page of a blob (32- or 64-bit, depending on the vcpu mode) to guest +memory. + +struct kvm_xen_hvm_config { + __u32 flags; + __u32 msr; + __u64 blob_addr_32; + __u64 blob_addr_64; + __u8 blob_size_32; + __u8 blob_size_64; + __u8 pad2[30]; +}; + + +4.29 KVM_GET_CLOCK + +Capability: KVM_CAP_ADJUST_CLOCK +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_clock_data (out) +Returns: 0 on success, -1 on error + +Gets the current timestamp of kvmclock as seen by the current guest. In +conjunction with KVM_SET_CLOCK, it is used to ensure monotonicity on scenarios +such as migration. + +When KVM_CAP_ADJUST_CLOCK is passed to KVM_CHECK_EXTENSION, it returns the +set of bits that KVM can return in struct kvm_clock_data's flag member. + +The only flag defined now is KVM_CLOCK_TSC_STABLE. If set, the returned +value is the exact kvmclock value seen by all VCPUs at the instant +when KVM_GET_CLOCK was called. If clear, the returned value is simply +CLOCK_MONOTONIC plus a constant offset; the offset can be modified +with KVM_SET_CLOCK. KVM will try to make all VCPUs follow this clock, +but the exact value read by each VCPU could differ, because the host +TSC is not stable. + +struct kvm_clock_data { + __u64 clock; /* kvmclock current value */ + __u32 flags; + __u32 pad[9]; +}; + + +4.30 KVM_SET_CLOCK + +Capability: KVM_CAP_ADJUST_CLOCK +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_clock_data (in) +Returns: 0 on success, -1 on error + +Sets the current timestamp of kvmclock to the value specified in its parameter. +In conjunction with KVM_GET_CLOCK, it is used to ensure monotonicity on scenarios +such as migration. + +struct kvm_clock_data { + __u64 clock; /* kvmclock current value */ + __u32 flags; + __u32 pad[9]; +}; + + +4.31 KVM_GET_VCPU_EVENTS + +Capability: KVM_CAP_VCPU_EVENTS +Extended by: KVM_CAP_INTR_SHADOW +Architectures: x86, arm, arm64 +Type: vcpu ioctl +Parameters: struct kvm_vcpu_event (out) +Returns: 0 on success, -1 on error + +X86: + +Gets currently pending exceptions, interrupts, and NMIs as well as related +states of the vcpu. + +struct kvm_vcpu_events { + struct { + __u8 injected; + __u8 nr; + __u8 has_error_code; + __u8 pending; + __u32 error_code; + } exception; + struct { + __u8 injected; + __u8 nr; + __u8 soft; + __u8 shadow; + } interrupt; + struct { + __u8 injected; + __u8 pending; + __u8 masked; + __u8 pad; + } nmi; + __u32 sipi_vector; + __u32 flags; + struct { + __u8 smm; + __u8 pending; + __u8 smm_inside_nmi; + __u8 latched_init; + } smi; + __u8 reserved[27]; + __u8 exception_has_payload; + __u64 exception_payload; +}; + +The following bits are defined in the flags field: + +- KVM_VCPUEVENT_VALID_SHADOW may be set to signal that + interrupt.shadow contains a valid state. + +- KVM_VCPUEVENT_VALID_SMM may be set to signal that smi contains a + valid state. + +- KVM_VCPUEVENT_VALID_PAYLOAD may be set to signal that the + exception_has_payload, exception_payload, and exception.pending + fields contain a valid state. This bit will be set whenever + KVM_CAP_EXCEPTION_PAYLOAD is enabled. + +ARM/ARM64: + +If the guest accesses a device that is being emulated by the host kernel in +such a way that a real device would generate a physical SError, KVM may make +a virtual SError pending for that VCPU. This system error interrupt remains +pending until the guest takes the exception by unmasking PSTATE.A. + +Running the VCPU may cause it to take a pending SError, or make an access that +causes an SError to become pending. The event's description is only valid while +the VPCU is not running. + +This API provides a way to read and write the pending 'event' state that is not +visible to the guest. To save, restore or migrate a VCPU the struct representing +the state can be read then written using this GET/SET API, along with the other +guest-visible registers. It is not possible to 'cancel' an SError that has been +made pending. + +A device being emulated in user-space may also wish to generate an SError. To do +this the events structure can be populated by user-space. The current state +should be read first, to ensure no existing SError is pending. If an existing +SError is pending, the architecture's 'Multiple SError interrupts' rules should +be followed. (2.5.3 of DDI0587.a "ARM Reliability, Availability, and +Serviceability (RAS) Specification"). + +SError exceptions always have an ESR value. Some CPUs have the ability to +specify what the virtual SError's ESR value should be. These systems will +advertise KVM_CAP_ARM_INJECT_SERROR_ESR. In this case exception.has_esr will +always have a non-zero value when read, and the agent making an SError pending +should specify the ISS field in the lower 24 bits of exception.serror_esr. If +the system supports KVM_CAP_ARM_INJECT_SERROR_ESR, but user-space sets the events +with exception.has_esr as zero, KVM will choose an ESR. + +Specifying exception.has_esr on a system that does not support it will return +-EINVAL. Setting anything other than the lower 24bits of exception.serror_esr +will return -EINVAL. + +struct kvm_vcpu_events { + struct { + __u8 serror_pending; + __u8 serror_has_esr; + /* Align it to 8 bytes */ + __u8 pad[6]; + __u64 serror_esr; + } exception; + __u32 reserved[12]; +}; + +4.32 KVM_SET_VCPU_EVENTS + +Capability: KVM_CAP_VCPU_EVENTS +Extended by: KVM_CAP_INTR_SHADOW +Architectures: x86, arm, arm64 +Type: vcpu ioctl +Parameters: struct kvm_vcpu_event (in) +Returns: 0 on success, -1 on error + +X86: + +Set pending exceptions, interrupts, and NMIs as well as related states of the +vcpu. + +See KVM_GET_VCPU_EVENTS for the data structure. + +Fields that may be modified asynchronously by running VCPUs can be excluded +from the update. These fields are nmi.pending, sipi_vector, smi.smm, +smi.pending. Keep the corresponding bits in the flags field cleared to +suppress overwriting the current in-kernel state. The bits are: + +KVM_VCPUEVENT_VALID_NMI_PENDING - transfer nmi.pending to the kernel +KVM_VCPUEVENT_VALID_SIPI_VECTOR - transfer sipi_vector +KVM_VCPUEVENT_VALID_SMM - transfer the smi sub-struct. + +If KVM_CAP_INTR_SHADOW is available, KVM_VCPUEVENT_VALID_SHADOW can be set in +the flags field to signal that interrupt.shadow contains a valid state and +shall be written into the VCPU. + +KVM_VCPUEVENT_VALID_SMM can only be set if KVM_CAP_X86_SMM is available. + +If KVM_CAP_EXCEPTION_PAYLOAD is enabled, KVM_VCPUEVENT_VALID_PAYLOAD +can be set in the flags field to signal that the +exception_has_payload, exception_payload, and exception.pending fields +contain a valid state and shall be written into the VCPU. + +ARM/ARM64: + +Set the pending SError exception state for this VCPU. It is not possible to +'cancel' an Serror that has been made pending. + +See KVM_GET_VCPU_EVENTS for the data structure. + + +4.33 KVM_GET_DEBUGREGS + +Capability: KVM_CAP_DEBUGREGS +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_debugregs (out) +Returns: 0 on success, -1 on error + +Reads debug registers from the vcpu. + +struct kvm_debugregs { + __u64 db[4]; + __u64 dr6; + __u64 dr7; + __u64 flags; + __u64 reserved[9]; +}; + + +4.34 KVM_SET_DEBUGREGS + +Capability: KVM_CAP_DEBUGREGS +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_debugregs (in) +Returns: 0 on success, -1 on error + +Writes debug registers into the vcpu. + +See KVM_GET_DEBUGREGS for the data structure. The flags field is unused +yet and must be cleared on entry. + + +4.35 KVM_SET_USER_MEMORY_REGION + +Capability: KVM_CAP_USER_MEMORY +Architectures: all +Type: vm ioctl +Parameters: struct kvm_userspace_memory_region (in) +Returns: 0 on success, -1 on error + +struct kvm_userspace_memory_region { + __u32 slot; + __u32 flags; + __u64 guest_phys_addr; + __u64 memory_size; /* bytes */ + __u64 userspace_addr; /* start of the userspace allocated memory */ +}; + +/* for kvm_memory_region::flags */ +#define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0) +#define KVM_MEM_READONLY (1UL << 1) + +This ioctl allows the user to create, modify or delete a guest physical +memory slot. Bits 0-15 of "slot" specify the slot id and this value +should be less than the maximum number of user memory slots supported per +VM. The maximum allowed slots can be queried using KVM_CAP_NR_MEMSLOTS. +Slots may not overlap in guest physical address space. + +If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 of "slot" +specifies the address space which is being modified. They must be +less than the value that KVM_CHECK_EXTENSION returns for the +KVM_CAP_MULTI_ADDRESS_SPACE capability. Slots in separate address spaces +are unrelated; the restriction on overlapping slots only applies within +each address space. + +Deleting a slot is done by passing zero for memory_size. When changing +an existing slot, it may be moved in the guest physical memory space, +or its flags may be modified, but it may not be resized. + +Memory for the region is taken starting at the address denoted by the +field userspace_addr, which must point at user addressable memory for +the entire memory slot size. Any object may back this memory, including +anonymous memory, ordinary files, and hugetlbfs. + +It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr +be identical. This allows large pages in the guest to be backed by large +pages in the host. + +The flags field supports two flags: KVM_MEM_LOG_DIRTY_PAGES and +KVM_MEM_READONLY. The former can be set to instruct KVM to keep track of +writes to memory within the slot. See KVM_GET_DIRTY_LOG ioctl to know how to +use it. The latter can be set, if KVM_CAP_READONLY_MEM capability allows it, +to make a new slot read-only. In this case, writes to this memory will be +posted to userspace as KVM_EXIT_MMIO exits. + +When the KVM_CAP_SYNC_MMU capability is available, changes in the backing of +the memory region are automatically reflected into the guest. For example, an +mmap() that affects the region will be made visible immediately. Another +example is madvise(MADV_DROP). + +It is recommended to use this API instead of the KVM_SET_MEMORY_REGION ioctl. +The KVM_SET_MEMORY_REGION does not allow fine grained control over memory +allocation and is deprecated. + + +4.36 KVM_SET_TSS_ADDR + +Capability: KVM_CAP_SET_TSS_ADDR +Architectures: x86 +Type: vm ioctl +Parameters: unsigned long tss_address (in) +Returns: 0 on success, -1 on error + +This ioctl defines the physical address of a three-page region in the guest +physical address space. The region must be within the first 4GB of the +guest physical address space and must not conflict with any memory slot +or any mmio address. The guest may malfunction if it accesses this memory +region. + +This ioctl is required on Intel-based hosts. This is needed on Intel hardware +because of a quirk in the virtualization implementation (see the internals +documentation when it pops into existence). + + +4.37 KVM_ENABLE_CAP + +Capability: KVM_CAP_ENABLE_CAP +Architectures: mips, ppc, s390 +Type: vcpu ioctl +Parameters: struct kvm_enable_cap (in) +Returns: 0 on success; -1 on error + +Capability: KVM_CAP_ENABLE_CAP_VM +Architectures: all +Type: vcpu ioctl +Parameters: struct kvm_enable_cap (in) +Returns: 0 on success; -1 on error + ++Not all extensions are enabled by default. Using this ioctl the application +can enable an extension, making it available to the guest. + +On systems that do not support this ioctl, it always fails. On systems that +do support it, it only works for extensions that are supported for enablement. + +To check if a capability can be enabled, the KVM_CHECK_EXTENSION ioctl should +be used. + +struct kvm_enable_cap { + /* in */ + __u32 cap; + +The capability that is supposed to get enabled. + + __u32 flags; + +A bitfield indicating future enhancements. Has to be 0 for now. + + __u64 args[4]; + +Arguments for enabling a feature. If a feature needs initial values to +function properly, this is the place to put them. + + __u8 pad[64]; +}; + +The vcpu ioctl should be used for vcpu-specific capabilities, the vm ioctl +for vm-wide capabilities. + +4.38 KVM_GET_MP_STATE + +Capability: KVM_CAP_MP_STATE +Architectures: x86, s390, arm, arm64 +Type: vcpu ioctl +Parameters: struct kvm_mp_state (out) +Returns: 0 on success; -1 on error + +struct kvm_mp_state { + __u32 mp_state; +}; + +Returns the vcpu's current "multiprocessing state" (though also valid on +uniprocessor guests). + +Possible values are: + + - KVM_MP_STATE_RUNNABLE: the vcpu is currently running [x86,arm/arm64] + - KVM_MP_STATE_UNINITIALIZED: the vcpu is an application processor (AP) + which has not yet received an INIT signal [x86] + - KVM_MP_STATE_INIT_RECEIVED: the vcpu has received an INIT signal, and is + now ready for a SIPI [x86] + - KVM_MP_STATE_HALTED: the vcpu has executed a HLT instruction and + is waiting for an interrupt [x86] + - KVM_MP_STATE_SIPI_RECEIVED: the vcpu has just received a SIPI (vector + accessible via KVM_GET_VCPU_EVENTS) [x86] + - KVM_MP_STATE_STOPPED: the vcpu is stopped [s390,arm/arm64] + - KVM_MP_STATE_CHECK_STOP: the vcpu is in a special error state [s390] + - KVM_MP_STATE_OPERATING: the vcpu is operating (running or halted) + [s390] + - KVM_MP_STATE_LOAD: the vcpu is in a special load/startup state + [s390] + +On x86, this ioctl is only useful after KVM_CREATE_IRQCHIP. Without an +in-kernel irqchip, the multiprocessing state must be maintained by userspace on +these architectures. + +For arm/arm64: + +The only states that are valid are KVM_MP_STATE_STOPPED and +KVM_MP_STATE_RUNNABLE which reflect if the vcpu is paused or not. + +4.39 KVM_SET_MP_STATE + +Capability: KVM_CAP_MP_STATE +Architectures: x86, s390, arm, arm64 +Type: vcpu ioctl +Parameters: struct kvm_mp_state (in) +Returns: 0 on success; -1 on error + +Sets the vcpu's current "multiprocessing state"; see KVM_GET_MP_STATE for +arguments. + +On x86, this ioctl is only useful after KVM_CREATE_IRQCHIP. Without an +in-kernel irqchip, the multiprocessing state must be maintained by userspace on +these architectures. + +For arm/arm64: + +The only states that are valid are KVM_MP_STATE_STOPPED and +KVM_MP_STATE_RUNNABLE which reflect if the vcpu should be paused or not. + +4.40 KVM_SET_IDENTITY_MAP_ADDR + +Capability: KVM_CAP_SET_IDENTITY_MAP_ADDR +Architectures: x86 +Type: vm ioctl +Parameters: unsigned long identity (in) +Returns: 0 on success, -1 on error + +This ioctl defines the physical address of a one-page region in the guest +physical address space. The region must be within the first 4GB of the +guest physical address space and must not conflict with any memory slot +or any mmio address. The guest may malfunction if it accesses this memory +region. + +Setting the address to 0 will result in resetting the address to its default +(0xfffbc000). + +This ioctl is required on Intel-based hosts. This is needed on Intel hardware +because of a quirk in the virtualization implementation (see the internals +documentation when it pops into existence). + +Fails if any VCPU has already been created. + +4.41 KVM_SET_BOOT_CPU_ID + +Capability: KVM_CAP_SET_BOOT_CPU_ID +Architectures: x86 +Type: vm ioctl +Parameters: unsigned long vcpu_id +Returns: 0 on success, -1 on error + +Define which vcpu is the Bootstrap Processor (BSP). Values are the same +as the vcpu id in KVM_CREATE_VCPU. If this ioctl is not called, the default +is vcpu 0. + + +4.42 KVM_GET_XSAVE + +Capability: KVM_CAP_XSAVE +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_xsave (out) +Returns: 0 on success, -1 on error + +struct kvm_xsave { + __u32 region[1024]; +}; + +This ioctl would copy current vcpu's xsave struct to the userspace. + + +4.43 KVM_SET_XSAVE + +Capability: KVM_CAP_XSAVE +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_xsave (in) +Returns: 0 on success, -1 on error + +struct kvm_xsave { + __u32 region[1024]; +}; + +This ioctl would copy userspace's xsave struct to the kernel. + + +4.44 KVM_GET_XCRS + +Capability: KVM_CAP_XCRS +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_xcrs (out) +Returns: 0 on success, -1 on error + +struct kvm_xcr { + __u32 xcr; + __u32 reserved; + __u64 value; +}; + +struct kvm_xcrs { + __u32 nr_xcrs; + __u32 flags; + struct kvm_xcr xcrs[KVM_MAX_XCRS]; + __u64 padding[16]; +}; + +This ioctl would copy current vcpu's xcrs to the userspace. + + +4.45 KVM_SET_XCRS + +Capability: KVM_CAP_XCRS +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_xcrs (in) +Returns: 0 on success, -1 on error + +struct kvm_xcr { + __u32 xcr; + __u32 reserved; + __u64 value; +}; + +struct kvm_xcrs { + __u32 nr_xcrs; + __u32 flags; + struct kvm_xcr xcrs[KVM_MAX_XCRS]; + __u64 padding[16]; +}; + +This ioctl would set vcpu's xcr to the value userspace specified. + + +4.46 KVM_GET_SUPPORTED_CPUID + +Capability: KVM_CAP_EXT_CPUID +Architectures: x86 +Type: system ioctl +Parameters: struct kvm_cpuid2 (in/out) +Returns: 0 on success, -1 on error + +struct kvm_cpuid2 { + __u32 nent; + __u32 padding; + struct kvm_cpuid_entry2 entries[0]; +}; + +#define KVM_CPUID_FLAG_SIGNIFCANT_INDEX BIT(0) +#define KVM_CPUID_FLAG_STATEFUL_FUNC BIT(1) +#define KVM_CPUID_FLAG_STATE_READ_NEXT BIT(2) + +struct kvm_cpuid_entry2 { + __u32 function; + __u32 index; + __u32 flags; + __u32 eax; + __u32 ebx; + __u32 ecx; + __u32 edx; + __u32 padding[3]; +}; + +This ioctl returns x86 cpuid features which are supported by both the +hardware and kvm in its default configuration. Userspace can use the +information returned by this ioctl to construct cpuid information (for +KVM_SET_CPUID2) that is consistent with hardware, kernel, and +userspace capabilities, and with user requirements (for example, the +user may wish to constrain cpuid to emulate older hardware, or for +feature consistency across a cluster). + +Note that certain capabilities, such as KVM_CAP_X86_DISABLE_EXITS, may +expose cpuid features (e.g. MONITOR) which are not supported by kvm in +its default configuration. If userspace enables such capabilities, it +is responsible for modifying the results of this ioctl appropriately. + +Userspace invokes KVM_GET_SUPPORTED_CPUID by passing a kvm_cpuid2 structure +with the 'nent' field indicating the number of entries in the variable-size +array 'entries'. If the number of entries is too low to describe the cpu +capabilities, an error (E2BIG) is returned. If the number is too high, +the 'nent' field is adjusted and an error (ENOMEM) is returned. If the +number is just right, the 'nent' field is adjusted to the number of valid +entries in the 'entries' array, which is then filled. + +The entries returned are the host cpuid as returned by the cpuid instruction, +with unknown or unsupported features masked out. Some features (for example, +x2apic), may not be present in the host cpu, but are exposed by kvm if it can +emulate them efficiently. The fields in each entry are defined as follows: + + function: the eax value used to obtain the entry + index: the ecx value used to obtain the entry (for entries that are + affected by ecx) + flags: an OR of zero or more of the following: + KVM_CPUID_FLAG_SIGNIFCANT_INDEX: + if the index field is valid + KVM_CPUID_FLAG_STATEFUL_FUNC: + if cpuid for this function returns different values for successive + invocations; there will be several entries with the same function, + all with this flag set + KVM_CPUID_FLAG_STATE_READ_NEXT: + for KVM_CPUID_FLAG_STATEFUL_FUNC entries, set if this entry is + the first entry to be read by a cpu + eax, ebx, ecx, edx: the values returned by the cpuid instruction for + this function/index combination + +The TSC deadline timer feature (CPUID leaf 1, ecx[24]) is always returned +as false, since the feature depends on KVM_CREATE_IRQCHIP for local APIC +support. Instead it is reported via + + ioctl(KVM_CHECK_EXTENSION, KVM_CAP_TSC_DEADLINE_TIMER) + +if that returns true and you use KVM_CREATE_IRQCHIP, or if you emulate the +feature in userspace, then you can enable the feature for KVM_SET_CPUID2. + + +4.47 KVM_PPC_GET_PVINFO + +Capability: KVM_CAP_PPC_GET_PVINFO +Architectures: ppc +Type: vm ioctl +Parameters: struct kvm_ppc_pvinfo (out) +Returns: 0 on success, !0 on error + +struct kvm_ppc_pvinfo { + __u32 flags; + __u32 hcall[4]; + __u8 pad[108]; +}; + +This ioctl fetches PV specific information that need to be passed to the guest +using the device tree or other means from vm context. + +The hcall array defines 4 instructions that make up a hypercall. + +If any additional field gets added to this structure later on, a bit for that +additional piece of information will be set in the flags bitmap. + +The flags bitmap is defined as: + + /* the host supports the ePAPR idle hcall + #define KVM_PPC_PVINFO_FLAGS_EV_IDLE (1<<0) + +4.52 KVM_SET_GSI_ROUTING + +Capability: KVM_CAP_IRQ_ROUTING +Architectures: x86 s390 arm arm64 +Type: vm ioctl +Parameters: struct kvm_irq_routing (in) +Returns: 0 on success, -1 on error + +Sets the GSI routing table entries, overwriting any previously set entries. + +On arm/arm64, GSI routing has the following limitation: +- GSI routing does not apply to KVM_IRQ_LINE but only to KVM_IRQFD. + +struct kvm_irq_routing { + __u32 nr; + __u32 flags; + struct kvm_irq_routing_entry entries[0]; +}; + +No flags are specified so far, the corresponding field must be set to zero. + +struct kvm_irq_routing_entry { + __u32 gsi; + __u32 type; + __u32 flags; + __u32 pad; + union { + struct kvm_irq_routing_irqchip irqchip; + struct kvm_irq_routing_msi msi; + struct kvm_irq_routing_s390_adapter adapter; + struct kvm_irq_routing_hv_sint hv_sint; + __u32 pad[8]; + } u; +}; + +/* gsi routing entry types */ +#define KVM_IRQ_ROUTING_IRQCHIP 1 +#define KVM_IRQ_ROUTING_MSI 2 +#define KVM_IRQ_ROUTING_S390_ADAPTER 3 +#define KVM_IRQ_ROUTING_HV_SINT 4 + +flags: +- KVM_MSI_VALID_DEVID: used along with KVM_IRQ_ROUTING_MSI routing entry + type, specifies that the devid field contains a valid value. The per-VM + KVM_CAP_MSI_DEVID capability advertises the requirement to provide + the device ID. If this capability is not available, userspace should + never set the KVM_MSI_VALID_DEVID flag as the ioctl might fail. +- zero otherwise + +struct kvm_irq_routing_irqchip { + __u32 irqchip; + __u32 pin; +}; + +struct kvm_irq_routing_msi { + __u32 address_lo; + __u32 address_hi; + __u32 data; + union { + __u32 pad; + __u32 devid; + }; +}; + +If KVM_MSI_VALID_DEVID is set, devid contains a unique device identifier +for the device that wrote the MSI message. For PCI, this is usually a +BFD identifier in the lower 16 bits. + +On x86, address_hi is ignored unless the KVM_X2APIC_API_USE_32BIT_IDS +feature of KVM_CAP_X2APIC_API capability is enabled. If it is enabled, +address_hi bits 31-8 provide bits 31-8 of the destination id. Bits 7-0 of +address_hi must be zero. + +struct kvm_irq_routing_s390_adapter { + __u64 ind_addr; + __u64 summary_addr; + __u64 ind_offset; + __u32 summary_offset; + __u32 adapter_id; +}; + +struct kvm_irq_routing_hv_sint { + __u32 vcpu; + __u32 sint; +}; + + +4.55 KVM_SET_TSC_KHZ + +Capability: KVM_CAP_TSC_CONTROL +Architectures: x86 +Type: vcpu ioctl +Parameters: virtual tsc_khz +Returns: 0 on success, -1 on error + +Specifies the tsc frequency for the virtual machine. The unit of the +frequency is KHz. + + +4.56 KVM_GET_TSC_KHZ + +Capability: KVM_CAP_GET_TSC_KHZ +Architectures: x86 +Type: vcpu ioctl +Parameters: none +Returns: virtual tsc-khz on success, negative value on error + +Returns the tsc frequency of the guest. The unit of the return value is +KHz. If the host has unstable tsc this ioctl returns -EIO instead as an +error. + + +4.57 KVM_GET_LAPIC + +Capability: KVM_CAP_IRQCHIP +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_lapic_state (out) +Returns: 0 on success, -1 on error + +#define KVM_APIC_REG_SIZE 0x400 +struct kvm_lapic_state { + char regs[KVM_APIC_REG_SIZE]; +}; + +Reads the Local APIC registers and copies them into the input argument. The +data format and layout are the same as documented in the architecture manual. + +If KVM_X2APIC_API_USE_32BIT_IDS feature of KVM_CAP_X2APIC_API is +enabled, then the format of APIC_ID register depends on the APIC mode +(reported by MSR_IA32_APICBASE) of its VCPU. x2APIC stores APIC ID in +the APIC_ID register (bytes 32-35). xAPIC only allows an 8-bit APIC ID +which is stored in bits 31-24 of the APIC register, or equivalently in +byte 35 of struct kvm_lapic_state's regs field. KVM_GET_LAPIC must then +be called after MSR_IA32_APICBASE has been set with KVM_SET_MSR. + +If KVM_X2APIC_API_USE_32BIT_IDS feature is disabled, struct kvm_lapic_state +always uses xAPIC format. + + +4.58 KVM_SET_LAPIC + +Capability: KVM_CAP_IRQCHIP +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_lapic_state (in) +Returns: 0 on success, -1 on error + +#define KVM_APIC_REG_SIZE 0x400 +struct kvm_lapic_state { + char regs[KVM_APIC_REG_SIZE]; +}; + +Copies the input argument into the Local APIC registers. The data format +and layout are the same as documented in the architecture manual. + +The format of the APIC ID register (bytes 32-35 of struct kvm_lapic_state's +regs field) depends on the state of the KVM_CAP_X2APIC_API capability. +See the note in KVM_GET_LAPIC. + + +4.59 KVM_IOEVENTFD + +Capability: KVM_CAP_IOEVENTFD +Architectures: all +Type: vm ioctl +Parameters: struct kvm_ioeventfd (in) +Returns: 0 on success, !0 on error + +This ioctl attaches or detaches an ioeventfd to a legal pio/mmio address +within the guest. A guest write in the registered address will signal the +provided event instead of triggering an exit. + +struct kvm_ioeventfd { + __u64 datamatch; + __u64 addr; /* legal pio/mmio address */ + __u32 len; /* 0, 1, 2, 4, or 8 bytes */ + __s32 fd; + __u32 flags; + __u8 pad[36]; +}; + +For the special case of virtio-ccw devices on s390, the ioevent is matched +to a subchannel/virtqueue tuple instead. + +The following flags are defined: + +#define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch) +#define KVM_IOEVENTFD_FLAG_PIO (1 << kvm_ioeventfd_flag_nr_pio) +#define KVM_IOEVENTFD_FLAG_DEASSIGN (1 << kvm_ioeventfd_flag_nr_deassign) +#define KVM_IOEVENTFD_FLAG_VIRTIO_CCW_NOTIFY \ + (1 << kvm_ioeventfd_flag_nr_virtio_ccw_notify) + +If datamatch flag is set, the event will be signaled only if the written value +to the registered address is equal to datamatch in struct kvm_ioeventfd. + +For virtio-ccw devices, addr contains the subchannel id and datamatch the +virtqueue index. + +With KVM_CAP_IOEVENTFD_ANY_LENGTH, a zero length ioeventfd is allowed, and +the kernel will ignore the length of guest write and may get a faster vmexit. +The speedup may only apply to specific architectures, but the ioeventfd will +work anyway. + +4.60 KVM_DIRTY_TLB + +Capability: KVM_CAP_SW_TLB +Architectures: ppc +Type: vcpu ioctl +Parameters: struct kvm_dirty_tlb (in) +Returns: 0 on success, -1 on error + +struct kvm_dirty_tlb { + __u64 bitmap; + __u32 num_dirty; +}; + +This must be called whenever userspace has changed an entry in the shared +TLB, prior to calling KVM_RUN on the associated vcpu. + +The "bitmap" field is the userspace address of an array. This array +consists of a number of bits, equal to the total number of TLB entries as +determined by the last successful call to KVM_CONFIG_TLB, rounded up to the +nearest multiple of 64. + +Each bit corresponds to one TLB entry, ordered the same as in the shared TLB +array. + +The array is little-endian: the bit 0 is the least significant bit of the +first byte, bit 8 is the least significant bit of the second byte, etc. +This avoids any complications with differing word sizes. + +The "num_dirty" field is a performance hint for KVM to determine whether it +should skip processing the bitmap and just invalidate everything. It must +be set to the number of set bits in the bitmap. + + +4.62 KVM_CREATE_SPAPR_TCE + +Capability: KVM_CAP_SPAPR_TCE +Architectures: powerpc +Type: vm ioctl +Parameters: struct kvm_create_spapr_tce (in) +Returns: file descriptor for manipulating the created TCE table + +This creates a virtual TCE (translation control entry) table, which +is an IOMMU for PAPR-style virtual I/O. It is used to translate +logical addresses used in virtual I/O into guest physical addresses, +and provides a scatter/gather capability for PAPR virtual I/O. + +/* for KVM_CAP_SPAPR_TCE */ +struct kvm_create_spapr_tce { + __u64 liobn; + __u32 window_size; +}; + +The liobn field gives the logical IO bus number for which to create a +TCE table. The window_size field specifies the size of the DMA window +which this TCE table will translate - the table will contain one 64 +bit TCE entry for every 4kiB of the DMA window. + +When the guest issues an H_PUT_TCE hcall on a liobn for which a TCE +table has been created using this ioctl(), the kernel will handle it +in real mode, updating the TCE table. H_PUT_TCE calls for other +liobns will cause a vm exit and must be handled by userspace. + +The return value is a file descriptor which can be passed to mmap(2) +to map the created TCE table into userspace. This lets userspace read +the entries written by kernel-handled H_PUT_TCE calls, and also lets +userspace update the TCE table directly which is useful in some +circumstances. + + +4.63 KVM_ALLOCATE_RMA + +Capability: KVM_CAP_PPC_RMA +Architectures: powerpc +Type: vm ioctl +Parameters: struct kvm_allocate_rma (out) +Returns: file descriptor for mapping the allocated RMA + +This allocates a Real Mode Area (RMA) from the pool allocated at boot +time by the kernel. An RMA is a physically-contiguous, aligned region +of memory used on older POWER processors to provide the memory which +will be accessed by real-mode (MMU off) accesses in a KVM guest. +POWER processors support a set of sizes for the RMA that usually +includes 64MB, 128MB, 256MB and some larger powers of two. + +/* for KVM_ALLOCATE_RMA */ +struct kvm_allocate_rma { + __u64 rma_size; +}; + +The return value is a file descriptor which can be passed to mmap(2) +to map the allocated RMA into userspace. The mapped area can then be +passed to the KVM_SET_USER_MEMORY_REGION ioctl to establish it as the +RMA for a virtual machine. The size of the RMA in bytes (which is +fixed at host kernel boot time) is returned in the rma_size field of +the argument structure. + +The KVM_CAP_PPC_RMA capability is 1 or 2 if the KVM_ALLOCATE_RMA ioctl +is supported; 2 if the processor requires all virtual machines to have +an RMA, or 1 if the processor can use an RMA but doesn't require it, +because it supports the Virtual RMA (VRMA) facility. + + +4.64 KVM_NMI + +Capability: KVM_CAP_USER_NMI +Architectures: x86 +Type: vcpu ioctl +Parameters: none +Returns: 0 on success, -1 on error + +Queues an NMI on the thread's vcpu. Note this is well defined only +when KVM_CREATE_IRQCHIP has not been called, since this is an interface +between the virtual cpu core and virtual local APIC. After KVM_CREATE_IRQCHIP +has been called, this interface is completely emulated within the kernel. + +To use this to emulate the LINT1 input with KVM_CREATE_IRQCHIP, use the +following algorithm: + + - pause the vcpu + - read the local APIC's state (KVM_GET_LAPIC) + - check whether changing LINT1 will queue an NMI (see the LVT entry for LINT1) + - if so, issue KVM_NMI + - resume the vcpu + +Some guests configure the LINT1 NMI input to cause a panic, aiding in +debugging. + + +4.65 KVM_S390_UCAS_MAP + +Capability: KVM_CAP_S390_UCONTROL +Architectures: s390 +Type: vcpu ioctl +Parameters: struct kvm_s390_ucas_mapping (in) +Returns: 0 in case of success + +The parameter is defined like this: + struct kvm_s390_ucas_mapping { + __u64 user_addr; + __u64 vcpu_addr; + __u64 length; + }; + +This ioctl maps the memory at "user_addr" with the length "length" to +the vcpu's address space starting at "vcpu_addr". All parameters need to +be aligned by 1 megabyte. + + +4.66 KVM_S390_UCAS_UNMAP + +Capability: KVM_CAP_S390_UCONTROL +Architectures: s390 +Type: vcpu ioctl +Parameters: struct kvm_s390_ucas_mapping (in) +Returns: 0 in case of success + +The parameter is defined like this: + struct kvm_s390_ucas_mapping { + __u64 user_addr; + __u64 vcpu_addr; + __u64 length; + }; + +This ioctl unmaps the memory in the vcpu's address space starting at +"vcpu_addr" with the length "length". The field "user_addr" is ignored. +All parameters need to be aligned by 1 megabyte. + + +4.67 KVM_S390_VCPU_FAULT + +Capability: KVM_CAP_S390_UCONTROL +Architectures: s390 +Type: vcpu ioctl +Parameters: vcpu absolute address (in) +Returns: 0 in case of success + +This call creates a page table entry on the virtual cpu's address space +(for user controlled virtual machines) or the virtual machine's address +space (for regular virtual machines). This only works for minor faults, +thus it's recommended to access subject memory page via the user page +table upfront. This is useful to handle validity intercepts for user +controlled virtual machines to fault in the virtual cpu's lowcore pages +prior to calling the KVM_RUN ioctl. + + +4.68 KVM_SET_ONE_REG + +Capability: KVM_CAP_ONE_REG +Architectures: all +Type: vcpu ioctl +Parameters: struct kvm_one_reg (in) +Returns: 0 on success, negative value on failure +Errors: + Â ENOENT: Â Â no such register + Â EINVAL: Â Â invalid register ID, or no such register + Â EPERM: Â Â Â (arm64) register access not allowed before vcpu finalization +(These error codes are indicative only: do not rely on a specific error +code being returned in a specific situation.) + +struct kvm_one_reg { + __u64 id; + __u64 addr; +}; + +Using this ioctl, a single vcpu register can be set to a specific value +defined by user space with the passed in struct kvm_one_reg, where id +refers to the register identifier as described below and addr is a pointer +to a variable with the respective size. There can be architecture agnostic +and architecture specific registers. Each have their own range of operation +and their own constants and width. To keep track of the implemented +registers, find a list below: + + Arch | Register | Width (bits) + | | + PPC | KVM_REG_PPC_HIOR | 64 + PPC | KVM_REG_PPC_IAC1 | 64 + PPC | KVM_REG_PPC_IAC2 | 64 + PPC | KVM_REG_PPC_IAC3 | 64 + PPC | KVM_REG_PPC_IAC4 | 64 + PPC | KVM_REG_PPC_DAC1 | 64 + PPC | KVM_REG_PPC_DAC2 | 64 + PPC | KVM_REG_PPC_DABR | 64 + PPC | KVM_REG_PPC_DSCR | 64 + PPC | KVM_REG_PPC_PURR | 64 + PPC | KVM_REG_PPC_SPURR | 64 + PPC | KVM_REG_PPC_DAR | 64 + PPC | KVM_REG_PPC_DSISR | 32 + PPC | KVM_REG_PPC_AMR | 64 + PPC | KVM_REG_PPC_UAMOR | 64 + PPC | KVM_REG_PPC_MMCR0 | 64 + PPC | KVM_REG_PPC_MMCR1 | 64 + PPC | KVM_REG_PPC_MMCRA | 64 + PPC | KVM_REG_PPC_MMCR2 | 64 + PPC | KVM_REG_PPC_MMCRS | 64 + PPC | KVM_REG_PPC_SIAR | 64 + PPC | KVM_REG_PPC_SDAR | 64 + PPC | KVM_REG_PPC_SIER | 64 + PPC | KVM_REG_PPC_PMC1 | 32 + PPC | KVM_REG_PPC_PMC2 | 32 + PPC | KVM_REG_PPC_PMC3 | 32 + PPC | KVM_REG_PPC_PMC4 | 32 + PPC | KVM_REG_PPC_PMC5 | 32 + PPC | KVM_REG_PPC_PMC6 | 32 + PPC | KVM_REG_PPC_PMC7 | 32 + PPC | KVM_REG_PPC_PMC8 | 32 + PPC | KVM_REG_PPC_FPR0 | 64 + ... + PPC | KVM_REG_PPC_FPR31 | 64 + PPC | KVM_REG_PPC_VR0 | 128 + ... + PPC | KVM_REG_PPC_VR31 | 128 + PPC | KVM_REG_PPC_VSR0 | 128 + ... + PPC | KVM_REG_PPC_VSR31 | 128 + PPC | KVM_REG_PPC_FPSCR | 64 + PPC | KVM_REG_PPC_VSCR | 32 + PPC | KVM_REG_PPC_VPA_ADDR | 64 + PPC | KVM_REG_PPC_VPA_SLB | 128 + PPC | KVM_REG_PPC_VPA_DTL | 128 + PPC | KVM_REG_PPC_EPCR | 32 + PPC | KVM_REG_PPC_EPR | 32 + PPC | KVM_REG_PPC_TCR | 32 + PPC | KVM_REG_PPC_TSR | 32 + PPC | KVM_REG_PPC_OR_TSR | 32 + PPC | KVM_REG_PPC_CLEAR_TSR | 32 + PPC | KVM_REG_PPC_MAS0 | 32 + PPC | KVM_REG_PPC_MAS1 | 32 + PPC | KVM_REG_PPC_MAS2 | 64 + PPC | KVM_REG_PPC_MAS7_3 | 64 + PPC | KVM_REG_PPC_MAS4 | 32 + PPC | KVM_REG_PPC_MAS6 | 32 + PPC | KVM_REG_PPC_MMUCFG | 32 + PPC | KVM_REG_PPC_TLB0CFG | 32 + PPC | KVM_REG_PPC_TLB1CFG | 32 + PPC | KVM_REG_PPC_TLB2CFG | 32 + PPC | KVM_REG_PPC_TLB3CFG | 32 + PPC | KVM_REG_PPC_TLB0PS | 32 + PPC | KVM_REG_PPC_TLB1PS | 32 + PPC | KVM_REG_PPC_TLB2PS | 32 + PPC | KVM_REG_PPC_TLB3PS | 32 + PPC | KVM_REG_PPC_EPTCFG | 32 + PPC | KVM_REG_PPC_ICP_STATE | 64 + PPC | KVM_REG_PPC_VP_STATE | 128 + PPC | KVM_REG_PPC_TB_OFFSET | 64 + PPC | KVM_REG_PPC_SPMC1 | 32 + PPC | KVM_REG_PPC_SPMC2 | 32 + PPC | KVM_REG_PPC_IAMR | 64 + PPC | KVM_REG_PPC_TFHAR | 64 + PPC | KVM_REG_PPC_TFIAR | 64 + PPC | KVM_REG_PPC_TEXASR | 64 + PPC | KVM_REG_PPC_FSCR | 64 + PPC | KVM_REG_PPC_PSPB | 32 + PPC | KVM_REG_PPC_EBBHR | 64 + PPC | KVM_REG_PPC_EBBRR | 64 + PPC | KVM_REG_PPC_BESCR | 64 + PPC | KVM_REG_PPC_TAR | 64 + PPC | KVM_REG_PPC_DPDES | 64 + PPC | KVM_REG_PPC_DAWR | 64 + PPC | KVM_REG_PPC_DAWRX | 64 + PPC | KVM_REG_PPC_CIABR | 64 + PPC | KVM_REG_PPC_IC | 64 + PPC | KVM_REG_PPC_VTB | 64 + PPC | KVM_REG_PPC_CSIGR | 64 + PPC | KVM_REG_PPC_TACR | 64 + PPC | KVM_REG_PPC_TCSCR | 64 + PPC | KVM_REG_PPC_PID | 64 + PPC | KVM_REG_PPC_ACOP | 64 + PPC | KVM_REG_PPC_VRSAVE | 32 + PPC | KVM_REG_PPC_LPCR | 32 + PPC | KVM_REG_PPC_LPCR_64 | 64 + PPC | KVM_REG_PPC_PPR | 64 + PPC | KVM_REG_PPC_ARCH_COMPAT | 32 + PPC | KVM_REG_PPC_DABRX | 32 + PPC | KVM_REG_PPC_WORT | 64 + PPC | KVM_REG_PPC_SPRG9 | 64 + PPC | KVM_REG_PPC_DBSR | 32 + PPC | KVM_REG_PPC_TIDR | 64 + PPC | KVM_REG_PPC_PSSCR | 64 + PPC | KVM_REG_PPC_DEC_EXPIRY | 64 + PPC | KVM_REG_PPC_PTCR | 64 + PPC | KVM_REG_PPC_TM_GPR0 | 64 + ... + PPC | KVM_REG_PPC_TM_GPR31 | 64 + PPC | KVM_REG_PPC_TM_VSR0 | 128 + ... + PPC | KVM_REG_PPC_TM_VSR63 | 128 + PPC | KVM_REG_PPC_TM_CR | 64 + PPC | KVM_REG_PPC_TM_LR | 64 + PPC | KVM_REG_PPC_TM_CTR | 64 + PPC | KVM_REG_PPC_TM_FPSCR | 64 + PPC | KVM_REG_PPC_TM_AMR | 64 + PPC | KVM_REG_PPC_TM_PPR | 64 + PPC | KVM_REG_PPC_TM_VRSAVE | 64 + PPC | KVM_REG_PPC_TM_VSCR | 32 + PPC | KVM_REG_PPC_TM_DSCR | 64 + PPC | KVM_REG_PPC_TM_TAR | 64 + PPC | KVM_REG_PPC_TM_XER | 64 + | | + MIPS | KVM_REG_MIPS_R0 | 64 + ... + MIPS | KVM_REG_MIPS_R31 | 64 + MIPS | KVM_REG_MIPS_HI | 64 + MIPS | KVM_REG_MIPS_LO | 64 + MIPS | KVM_REG_MIPS_PC | 64 + MIPS | KVM_REG_MIPS_CP0_INDEX | 32 + MIPS | KVM_REG_MIPS_CP0_ENTRYLO0 | 64 + MIPS | KVM_REG_MIPS_CP0_ENTRYLO1 | 64 + MIPS | KVM_REG_MIPS_CP0_CONTEXT | 64 + MIPS | KVM_REG_MIPS_CP0_CONTEXTCONFIG| 32 + MIPS | KVM_REG_MIPS_CP0_USERLOCAL | 64 + MIPS | KVM_REG_MIPS_CP0_XCONTEXTCONFIG| 64 + MIPS | KVM_REG_MIPS_CP0_PAGEMASK | 32 + MIPS | KVM_REG_MIPS_CP0_PAGEGRAIN | 32 + MIPS | KVM_REG_MIPS_CP0_SEGCTL0 | 64 + MIPS | KVM_REG_MIPS_CP0_SEGCTL1 | 64 + MIPS | KVM_REG_MIPS_CP0_SEGCTL2 | 64 + MIPS | KVM_REG_MIPS_CP0_PWBASE | 64 + MIPS | KVM_REG_MIPS_CP0_PWFIELD | 64 + MIPS | KVM_REG_MIPS_CP0_PWSIZE | 64 + MIPS | KVM_REG_MIPS_CP0_WIRED | 32 + MIPS | KVM_REG_MIPS_CP0_PWCTL | 32 + MIPS | KVM_REG_MIPS_CP0_HWRENA | 32 + MIPS | KVM_REG_MIPS_CP0_BADVADDR | 64 + MIPS | KVM_REG_MIPS_CP0_BADINSTR | 32 + MIPS | KVM_REG_MIPS_CP0_BADINSTRP | 32 + MIPS | KVM_REG_MIPS_CP0_COUNT | 32 + MIPS | KVM_REG_MIPS_CP0_ENTRYHI | 64 + MIPS | KVM_REG_MIPS_CP0_COMPARE | 32 + MIPS | KVM_REG_MIPS_CP0_STATUS | 32 + MIPS | KVM_REG_MIPS_CP0_INTCTL | 32 + MIPS | KVM_REG_MIPS_CP0_CAUSE | 32 + MIPS | KVM_REG_MIPS_CP0_EPC | 64 + MIPS | KVM_REG_MIPS_CP0_PRID | 32 + MIPS | KVM_REG_MIPS_CP0_EBASE | 64 + MIPS | KVM_REG_MIPS_CP0_CONFIG | 32 + MIPS | KVM_REG_MIPS_CP0_CONFIG1 | 32 + MIPS | KVM_REG_MIPS_CP0_CONFIG2 | 32 + MIPS | KVM_REG_MIPS_CP0_CONFIG3 | 32 + MIPS | KVM_REG_MIPS_CP0_CONFIG4 | 32 + MIPS | KVM_REG_MIPS_CP0_CONFIG5 | 32 + MIPS | KVM_REG_MIPS_CP0_CONFIG7 | 32 + MIPS | KVM_REG_MIPS_CP0_XCONTEXT | 64 + MIPS | KVM_REG_MIPS_CP0_ERROREPC | 64 + MIPS | KVM_REG_MIPS_CP0_KSCRATCH1 | 64 + MIPS | KVM_REG_MIPS_CP0_KSCRATCH2 | 64 + MIPS | KVM_REG_MIPS_CP0_KSCRATCH3 | 64 + MIPS | KVM_REG_MIPS_CP0_KSCRATCH4 | 64 + MIPS | KVM_REG_MIPS_CP0_KSCRATCH5 | 64 + MIPS | KVM_REG_MIPS_CP0_KSCRATCH6 | 64 + MIPS | KVM_REG_MIPS_CP0_MAAR(0..63) | 64 + MIPS | KVM_REG_MIPS_COUNT_CTL | 64 + MIPS | KVM_REG_MIPS_COUNT_RESUME | 64 + MIPS | KVM_REG_MIPS_COUNT_HZ | 64 + MIPS | KVM_REG_MIPS_FPR_32(0..31) | 32 + MIPS | KVM_REG_MIPS_FPR_64(0..31) | 64 + MIPS | KVM_REG_MIPS_VEC_128(0..31) | 128 + MIPS | KVM_REG_MIPS_FCR_IR | 32 + MIPS | KVM_REG_MIPS_FCR_CSR | 32 + MIPS | KVM_REG_MIPS_MSA_IR | 32 + MIPS | KVM_REG_MIPS_MSA_CSR | 32 + +ARM registers are mapped using the lower 32 bits. The upper 16 of that +is the register group type, or coprocessor number: + +ARM core registers have the following id bit patterns: + 0x4020 0000 0010 <index into the kvm_regs struct:16> + +ARM 32-bit CP15 registers have the following id bit patterns: + 0x4020 0000 000F <zero:1> <crn:4> <crm:4> <opc1:4> <opc2:3> + +ARM 64-bit CP15 registers have the following id bit patterns: + 0x4030 0000 000F <zero:1> <zero:4> <crm:4> <opc1:4> <zero:3> + +ARM CCSIDR registers are demultiplexed by CSSELR value: + 0x4020 0000 0011 00 <csselr:8> + +ARM 32-bit VFP control registers have the following id bit patterns: + 0x4020 0000 0012 1 <regno:12> + +ARM 64-bit FP registers have the following id bit patterns: + 0x4030 0000 0012 0 <regno:12> + +ARM firmware pseudo-registers have the following bit pattern: + 0x4030 0000 0014 <regno:16> + + +arm64 registers are mapped using the lower 32 bits. The upper 16 of +that is the register group type, or coprocessor number: + +arm64 core/FP-SIMD registers have the following id bit patterns. Note +that the size of the access is variable, as the kvm_regs structure +contains elements ranging from 32 to 128 bits. The index is a 32bit +value in the kvm_regs structure seen as a 32bit array. + 0x60x0 0000 0010 <index into the kvm_regs struct:16> + +Specifically: + Encoding Register Bits kvm_regs member +---------------------------------------------------------------- + 0x6030 0000 0010 0000 X0 64 regs.regs[0] + 0x6030 0000 0010 0002 X1 64 regs.regs[1] + ... + 0x6030 0000 0010 003c X30 64 regs.regs[30] + 0x6030 0000 0010 003e SP 64 regs.sp + 0x6030 0000 0010 0040 PC 64 regs.pc + 0x6030 0000 0010 0042 PSTATE 64 regs.pstate + 0x6030 0000 0010 0044 SP_EL1 64 sp_el1 + 0x6030 0000 0010 0046 ELR_EL1 64 elr_el1 + 0x6030 0000 0010 0048 SPSR_EL1 64 spsr[KVM_SPSR_EL1] (alias SPSR_SVC) + 0x6030 0000 0010 004a SPSR_ABT 64 spsr[KVM_SPSR_ABT] + 0x6030 0000 0010 004c SPSR_UND 64 spsr[KVM_SPSR_UND] + 0x6030 0000 0010 004e SPSR_IRQ 64 spsr[KVM_SPSR_IRQ] + 0x6060 0000 0010 0050 SPSR_FIQ 64 spsr[KVM_SPSR_FIQ] + 0x6040 0000 0010 0054 V0 128 fp_regs.vregs[0] (*) + 0x6040 0000 0010 0058 V1 128 fp_regs.vregs[1] (*) + ... + 0x6040 0000 0010 00d0 V31 128 fp_regs.vregs[31] (*) + 0x6020 0000 0010 00d4 FPSR 32 fp_regs.fpsr + 0x6020 0000 0010 00d5 FPCR 32 fp_regs.fpcr + +(*) These encodings are not accepted for SVE-enabled vcpus. See + KVM_ARM_VCPU_INIT. + + The equivalent register content can be accessed via bits [127:0] of + the corresponding SVE Zn registers instead for vcpus that have SVE + enabled (see below). + +arm64 CCSIDR registers are demultiplexed by CSSELR value: + 0x6020 0000 0011 00 <csselr:8> + +arm64 system registers have the following id bit patterns: + 0x6030 0000 0013 <op0:2> <op1:3> <crn:4> <crm:4> <op2:3> + +arm64 firmware pseudo-registers have the following bit pattern: + 0x6030 0000 0014 <regno:16> + +arm64 SVE registers have the following bit patterns: + 0x6080 0000 0015 00 <n:5> <slice:5> Zn bits[2048*slice + 2047 : 2048*slice] + 0x6050 0000 0015 04 <n:4> <slice:5> Pn bits[256*slice + 255 : 256*slice] + 0x6050 0000 0015 060 <slice:5> FFR bits[256*slice + 255 : 256*slice] + 0x6060 0000 0015 ffff KVM_REG_ARM64_SVE_VLS pseudo-register + +Access to register IDs where 2048 * slice >= 128 * max_vq will fail with +ENOENT. max_vq is the vcpu's maximum supported vector length in 128-bit +quadwords: see (**) below. + +These registers are only accessible on vcpus for which SVE is enabled. +See KVM_ARM_VCPU_INIT for details. + +In addition, except for KVM_REG_ARM64_SVE_VLS, these registers are not +accessible until the vcpu's SVE configuration has been finalized +using KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE). See KVM_ARM_VCPU_INIT +and KVM_ARM_VCPU_FINALIZE for more information about this procedure. + +KVM_REG_ARM64_SVE_VLS is a pseudo-register that allows the set of vector +lengths supported by the vcpu to be discovered and configured by +userspace. When transferred to or from user memory via KVM_GET_ONE_REG +or KVM_SET_ONE_REG, the value of this register is of type +__u64[KVM_ARM64_SVE_VLS_WORDS], and encodes the set of vector lengths as +follows: + +__u64 vector_lengths[KVM_ARM64_SVE_VLS_WORDS]; + +if (vq >= SVE_VQ_MIN && vq <= SVE_VQ_MAX && + ((vector_lengths[(vq - KVM_ARM64_SVE_VQ_MIN) / 64] >> + ((vq - KVM_ARM64_SVE_VQ_MIN) % 64)) & 1)) + /* Vector length vq * 16 bytes supported */ +else + /* Vector length vq * 16 bytes not supported */ + +(**) The maximum value vq for which the above condition is true is +max_vq. This is the maximum vector length available to the guest on +this vcpu, and determines which register slices are visible through +this ioctl interface. + +(See Documentation/arm64/sve.rst for an explanation of the "vq" +nomenclature.) + +KVM_REG_ARM64_SVE_VLS is only accessible after KVM_ARM_VCPU_INIT. +KVM_ARM_VCPU_INIT initialises it to the best set of vector lengths that +the host supports. + +Userspace may subsequently modify it if desired until the vcpu's SVE +configuration is finalized using KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE). + +Apart from simply removing all vector lengths from the host set that +exceed some value, support for arbitrarily chosen sets of vector lengths +is hardware-dependent and may not be available. Attempting to configure +an invalid set of vector lengths via KVM_SET_ONE_REG will fail with +EINVAL. + +After the vcpu's SVE configuration is finalized, further attempts to +write this register will fail with EPERM. + + +MIPS registers are mapped using the lower 32 bits. The upper 16 of that is +the register group type: + +MIPS core registers (see above) have the following id bit patterns: + 0x7030 0000 0000 <reg:16> + +MIPS CP0 registers (see KVM_REG_MIPS_CP0_* above) have the following id bit +patterns depending on whether they're 32-bit or 64-bit registers: + 0x7020 0000 0001 00 <reg:5> <sel:3> (32-bit) + 0x7030 0000 0001 00 <reg:5> <sel:3> (64-bit) + +Note: KVM_REG_MIPS_CP0_ENTRYLO0 and KVM_REG_MIPS_CP0_ENTRYLO1 are the MIPS64 +versions of the EntryLo registers regardless of the word size of the host +hardware, host kernel, guest, and whether XPA is present in the guest, i.e. +with the RI and XI bits (if they exist) in bits 63 and 62 respectively, and +the PFNX field starting at bit 30. + +MIPS MAARs (see KVM_REG_MIPS_CP0_MAAR(*) above) have the following id bit +patterns: + 0x7030 0000 0001 01 <reg:8> + +MIPS KVM control registers (see above) have the following id bit patterns: + 0x7030 0000 0002 <reg:16> + +MIPS FPU registers (see KVM_REG_MIPS_FPR_{32,64}() above) have the following +id bit patterns depending on the size of the register being accessed. They are +always accessed according to the current guest FPU mode (Status.FR and +Config5.FRE), i.e. as the guest would see them, and they become unpredictable +if the guest FPU mode is changed. MIPS SIMD Architecture (MSA) vector +registers (see KVM_REG_MIPS_VEC_128() above) have similar patterns as they +overlap the FPU registers: + 0x7020 0000 0003 00 <0:3> <reg:5> (32-bit FPU registers) + 0x7030 0000 0003 00 <0:3> <reg:5> (64-bit FPU registers) + 0x7040 0000 0003 00 <0:3> <reg:5> (128-bit MSA vector registers) + +MIPS FPU control registers (see KVM_REG_MIPS_FCR_{IR,CSR} above) have the +following id bit patterns: + 0x7020 0000 0003 01 <0:3> <reg:5> + +MIPS MSA control registers (see KVM_REG_MIPS_MSA_{IR,CSR} above) have the +following id bit patterns: + 0x7020 0000 0003 02 <0:3> <reg:5> + + +4.69 KVM_GET_ONE_REG + +Capability: KVM_CAP_ONE_REG +Architectures: all +Type: vcpu ioctl +Parameters: struct kvm_one_reg (in and out) +Returns: 0 on success, negative value on failure +Errors include: + Â ENOENT: Â Â no such register + Â EINVAL: Â Â invalid register ID, or no such register + Â EPERM: Â Â Â (arm64) register access not allowed before vcpu finalization +(These error codes are indicative only: do not rely on a specific error +code being returned in a specific situation.) + +This ioctl allows to receive the value of a single register implemented +in a vcpu. The register to read is indicated by the "id" field of the +kvm_one_reg struct passed in. On success, the register value can be found +at the memory location pointed to by "addr". + +The list of registers accessible using this interface is identical to the +list in 4.68. + + +4.70 KVM_KVMCLOCK_CTRL + +Capability: KVM_CAP_KVMCLOCK_CTRL +Architectures: Any that implement pvclocks (currently x86 only) +Type: vcpu ioctl +Parameters: None +Returns: 0 on success, -1 on error + +This signals to the host kernel that the specified guest is being paused by +userspace. The host will set a flag in the pvclock structure that is checked +from the soft lockup watchdog. The flag is part of the pvclock structure that +is shared between guest and host, specifically the second bit of the flags +field of the pvclock_vcpu_time_info structure. It will be set exclusively by +the host and read/cleared exclusively by the guest. The guest operation of +checking and clearing the flag must an atomic operation so +load-link/store-conditional, or equivalent must be used. There are two cases +where the guest will clear the flag: when the soft lockup watchdog timer resets +itself or when a soft lockup is detected. This ioctl can be called any time +after pausing the vcpu, but before it is resumed. + + +4.71 KVM_SIGNAL_MSI + +Capability: KVM_CAP_SIGNAL_MSI +Architectures: x86 arm arm64 +Type: vm ioctl +Parameters: struct kvm_msi (in) +Returns: >0 on delivery, 0 if guest blocked the MSI, and -1 on error + +Directly inject a MSI message. Only valid with in-kernel irqchip that handles +MSI messages. + +struct kvm_msi { + __u32 address_lo; + __u32 address_hi; + __u32 data; + __u32 flags; + __u32 devid; + __u8 pad[12]; +}; + +flags: KVM_MSI_VALID_DEVID: devid contains a valid value. The per-VM + KVM_CAP_MSI_DEVID capability advertises the requirement to provide + the device ID. If this capability is not available, userspace + should never set the KVM_MSI_VALID_DEVID flag as the ioctl might fail. + +If KVM_MSI_VALID_DEVID is set, devid contains a unique device identifier +for the device that wrote the MSI message. For PCI, this is usually a +BFD identifier in the lower 16 bits. + +On x86, address_hi is ignored unless the KVM_X2APIC_API_USE_32BIT_IDS +feature of KVM_CAP_X2APIC_API capability is enabled. If it is enabled, +address_hi bits 31-8 provide bits 31-8 of the destination id. Bits 7-0 of +address_hi must be zero. + + +4.71 KVM_CREATE_PIT2 + +Capability: KVM_CAP_PIT2 +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_pit_config (in) +Returns: 0 on success, -1 on error + +Creates an in-kernel device model for the i8254 PIT. This call is only valid +after enabling in-kernel irqchip support via KVM_CREATE_IRQCHIP. The following +parameters have to be passed: + +struct kvm_pit_config { + __u32 flags; + __u32 pad[15]; +}; + +Valid flags are: + +#define KVM_PIT_SPEAKER_DUMMY 1 /* emulate speaker port stub */ + +PIT timer interrupts may use a per-VM kernel thread for injection. If it +exists, this thread will have a name of the following pattern: + +kvm-pit/<owner-process-pid> + +When running a guest with elevated priorities, the scheduling parameters of +this thread may have to be adjusted accordingly. + +This IOCTL replaces the obsolete KVM_CREATE_PIT. + + +4.72 KVM_GET_PIT2 + +Capability: KVM_CAP_PIT_STATE2 +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_pit_state2 (out) +Returns: 0 on success, -1 on error + +Retrieves the state of the in-kernel PIT model. Only valid after +KVM_CREATE_PIT2. The state is returned in the following structure: + +struct kvm_pit_state2 { + struct kvm_pit_channel_state channels[3]; + __u32 flags; + __u32 reserved[9]; +}; + +Valid flags are: + +/* disable PIT in HPET legacy mode */ +#define KVM_PIT_FLAGS_HPET_LEGACY 0x00000001 + +This IOCTL replaces the obsolete KVM_GET_PIT. + + +4.73 KVM_SET_PIT2 + +Capability: KVM_CAP_PIT_STATE2 +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_pit_state2 (in) +Returns: 0 on success, -1 on error + +Sets the state of the in-kernel PIT model. Only valid after KVM_CREATE_PIT2. +See KVM_GET_PIT2 for details on struct kvm_pit_state2. + +This IOCTL replaces the obsolete KVM_SET_PIT. + + +4.74 KVM_PPC_GET_SMMU_INFO + +Capability: KVM_CAP_PPC_GET_SMMU_INFO +Architectures: powerpc +Type: vm ioctl +Parameters: None +Returns: 0 on success, -1 on error + +This populates and returns a structure describing the features of +the "Server" class MMU emulation supported by KVM. +This can in turn be used by userspace to generate the appropriate +device-tree properties for the guest operating system. + +The structure contains some global information, followed by an +array of supported segment page sizes: + + struct kvm_ppc_smmu_info { + __u64 flags; + __u32 slb_size; + __u32 pad; + struct kvm_ppc_one_seg_page_size sps[KVM_PPC_PAGE_SIZES_MAX_SZ]; + }; + +The supported flags are: + + - KVM_PPC_PAGE_SIZES_REAL: + When that flag is set, guest page sizes must "fit" the backing + store page sizes. When not set, any page size in the list can + be used regardless of how they are backed by userspace. + + - KVM_PPC_1T_SEGMENTS + The emulated MMU supports 1T segments in addition to the + standard 256M ones. + + - KVM_PPC_NO_HASH + This flag indicates that HPT guests are not supported by KVM, + thus all guests must use radix MMU mode. + +The "slb_size" field indicates how many SLB entries are supported + +The "sps" array contains 8 entries indicating the supported base +page sizes for a segment in increasing order. Each entry is defined +as follow: + + struct kvm_ppc_one_seg_page_size { + __u32 page_shift; /* Base page shift of segment (or 0) */ + __u32 slb_enc; /* SLB encoding for BookS */ + struct kvm_ppc_one_page_size enc[KVM_PPC_PAGE_SIZES_MAX_SZ]; + }; + +An entry with a "page_shift" of 0 is unused. Because the array is +organized in increasing order, a lookup can stop when encoutering +such an entry. + +The "slb_enc" field provides the encoding to use in the SLB for the +page size. The bits are in positions such as the value can directly +be OR'ed into the "vsid" argument of the slbmte instruction. + +The "enc" array is a list which for each of those segment base page +size provides the list of supported actual page sizes (which can be +only larger or equal to the base page size), along with the +corresponding encoding in the hash PTE. Similarly, the array is +8 entries sorted by increasing sizes and an entry with a "0" shift +is an empty entry and a terminator: + + struct kvm_ppc_one_page_size { + __u32 page_shift; /* Page shift (or 0) */ + __u32 pte_enc; /* Encoding in the HPTE (>>12) */ + }; + +The "pte_enc" field provides a value that can OR'ed into the hash +PTE's RPN field (ie, it needs to be shifted left by 12 to OR it +into the hash PTE second double word). + +4.75 KVM_IRQFD + +Capability: KVM_CAP_IRQFD +Architectures: x86 s390 arm arm64 +Type: vm ioctl +Parameters: struct kvm_irqfd (in) +Returns: 0 on success, -1 on error + +Allows setting an eventfd to directly trigger a guest interrupt. +kvm_irqfd.fd specifies the file descriptor to use as the eventfd and +kvm_irqfd.gsi specifies the irqchip pin toggled by this event. When +an event is triggered on the eventfd, an interrupt is injected into +the guest using the specified gsi pin. The irqfd is removed using +the KVM_IRQFD_FLAG_DEASSIGN flag, specifying both kvm_irqfd.fd +and kvm_irqfd.gsi. + +With KVM_CAP_IRQFD_RESAMPLE, KVM_IRQFD supports a de-assert and notify +mechanism allowing emulation of level-triggered, irqfd-based +interrupts. When KVM_IRQFD_FLAG_RESAMPLE is set the user must pass an +additional eventfd in the kvm_irqfd.resamplefd field. When operating +in resample mode, posting of an interrupt through kvm_irq.fd asserts +the specified gsi in the irqchip. When the irqchip is resampled, such +as from an EOI, the gsi is de-asserted and the user is notified via +kvm_irqfd.resamplefd. It is the user's responsibility to re-queue +the interrupt if the device making use of it still requires service. +Note that closing the resamplefd is not sufficient to disable the +irqfd. The KVM_IRQFD_FLAG_RESAMPLE is only necessary on assignment +and need not be specified with KVM_IRQFD_FLAG_DEASSIGN. + +On arm/arm64, gsi routing being supported, the following can happen: +- in case no routing entry is associated to this gsi, injection fails +- in case the gsi is associated to an irqchip routing entry, + irqchip.pin + 32 corresponds to the injected SPI ID. +- in case the gsi is associated to an MSI routing entry, the MSI + message and device ID are translated into an LPI (support restricted + to GICv3 ITS in-kernel emulation). + +4.76 KVM_PPC_ALLOCATE_HTAB + +Capability: KVM_CAP_PPC_ALLOC_HTAB +Architectures: powerpc +Type: vm ioctl +Parameters: Pointer to u32 containing hash table order (in/out) +Returns: 0 on success, -1 on error + +This requests the host kernel to allocate an MMU hash table for a +guest using the PAPR paravirtualization interface. This only does +anything if the kernel is configured to use the Book 3S HV style of +virtualization. Otherwise the capability doesn't exist and the ioctl +returns an ENOTTY error. The rest of this description assumes Book 3S +HV. + +There must be no vcpus running when this ioctl is called; if there +are, it will do nothing and return an EBUSY error. + +The parameter is a pointer to a 32-bit unsigned integer variable +containing the order (log base 2) of the desired size of the hash +table, which must be between 18 and 46. On successful return from the +ioctl, the value will not be changed by the kernel. + +If no hash table has been allocated when any vcpu is asked to run +(with the KVM_RUN ioctl), the host kernel will allocate a +default-sized hash table (16 MB). + +If this ioctl is called when a hash table has already been allocated, +with a different order from the existing hash table, the existing hash +table will be freed and a new one allocated. If this is ioctl is +called when a hash table has already been allocated of the same order +as specified, the kernel will clear out the existing hash table (zero +all HPTEs). In either case, if the guest is using the virtualized +real-mode area (VRMA) facility, the kernel will re-create the VMRA +HPTEs on the next KVM_RUN of any vcpu. + +4.77 KVM_S390_INTERRUPT + +Capability: basic +Architectures: s390 +Type: vm ioctl, vcpu ioctl +Parameters: struct kvm_s390_interrupt (in) +Returns: 0 on success, -1 on error + +Allows to inject an interrupt to the guest. Interrupts can be floating +(vm ioctl) or per cpu (vcpu ioctl), depending on the interrupt type. + +Interrupt parameters are passed via kvm_s390_interrupt: + +struct kvm_s390_interrupt { + __u32 type; + __u32 parm; + __u64 parm64; +}; + +type can be one of the following: + +KVM_S390_SIGP_STOP (vcpu) - sigp stop; optional flags in parm +KVM_S390_PROGRAM_INT (vcpu) - program check; code in parm +KVM_S390_SIGP_SET_PREFIX (vcpu) - sigp set prefix; prefix address in parm +KVM_S390_RESTART (vcpu) - restart +KVM_S390_INT_CLOCK_COMP (vcpu) - clock comparator interrupt +KVM_S390_INT_CPU_TIMER (vcpu) - CPU timer interrupt +KVM_S390_INT_VIRTIO (vm) - virtio external interrupt; external interrupt + parameters in parm and parm64 +KVM_S390_INT_SERVICE (vm) - sclp external interrupt; sclp parameter in parm +KVM_S390_INT_EMERGENCY (vcpu) - sigp emergency; source cpu in parm +KVM_S390_INT_EXTERNAL_CALL (vcpu) - sigp external call; source cpu in parm +KVM_S390_INT_IO(ai,cssid,ssid,schid) (vm) - compound value to indicate an + I/O interrupt (ai - adapter interrupt; cssid,ssid,schid - subchannel); + I/O interruption parameters in parm (subchannel) and parm64 (intparm, + interruption subclass) +KVM_S390_MCHK (vm, vcpu) - machine check interrupt; cr 14 bits in parm, + machine check interrupt code in parm64 (note that + machine checks needing further payload are not + supported by this ioctl) + +This is an asynchronous vcpu ioctl and can be invoked from any thread. + +4.78 KVM_PPC_GET_HTAB_FD + +Capability: KVM_CAP_PPC_HTAB_FD +Architectures: powerpc +Type: vm ioctl +Parameters: Pointer to struct kvm_get_htab_fd (in) +Returns: file descriptor number (>= 0) on success, -1 on error + +This returns a file descriptor that can be used either to read out the +entries in the guest's hashed page table (HPT), or to write entries to +initialize the HPT. The returned fd can only be written to if the +KVM_GET_HTAB_WRITE bit is set in the flags field of the argument, and +can only be read if that bit is clear. The argument struct looks like +this: + +/* For KVM_PPC_GET_HTAB_FD */ +struct kvm_get_htab_fd { + __u64 flags; + __u64 start_index; + __u64 reserved[2]; +}; + +/* Values for kvm_get_htab_fd.flags */ +#define KVM_GET_HTAB_BOLTED_ONLY ((__u64)0x1) +#define KVM_GET_HTAB_WRITE ((__u64)0x2) + +The `start_index' field gives the index in the HPT of the entry at +which to start reading. It is ignored when writing. + +Reads on the fd will initially supply information about all +"interesting" HPT entries. Interesting entries are those with the +bolted bit set, if the KVM_GET_HTAB_BOLTED_ONLY bit is set, otherwise +all entries. When the end of the HPT is reached, the read() will +return. If read() is called again on the fd, it will start again from +the beginning of the HPT, but will only return HPT entries that have +changed since they were last read. + +Data read or written is structured as a header (8 bytes) followed by a +series of valid HPT entries (16 bytes) each. The header indicates how +many valid HPT entries there are and how many invalid entries follow +the valid entries. The invalid entries are not represented explicitly +in the stream. The header format is: + +struct kvm_get_htab_header { + __u32 index; + __u16 n_valid; + __u16 n_invalid; +}; + +Writes to the fd create HPT entries starting at the index given in the +header; first `n_valid' valid entries with contents from the data +written, then `n_invalid' invalid entries, invalidating any previously +valid entries found. + +4.79 KVM_CREATE_DEVICE + +Capability: KVM_CAP_DEVICE_CTRL +Type: vm ioctl +Parameters: struct kvm_create_device (in/out) +Returns: 0 on success, -1 on error +Errors: + ENODEV: The device type is unknown or unsupported + EEXIST: Device already created, and this type of device may not + be instantiated multiple times + + Other error conditions may be defined by individual device types or + have their standard meanings. + +Creates an emulated device in the kernel. The file descriptor returned +in fd can be used with KVM_SET/GET/HAS_DEVICE_ATTR. + +If the KVM_CREATE_DEVICE_TEST flag is set, only test whether the +device type is supported (not necessarily whether it can be created +in the current vm). + +Individual devices should not define flags. Attributes should be used +for specifying any behavior that is not implied by the device type +number. + +struct kvm_create_device { + __u32 type; /* in: KVM_DEV_TYPE_xxx */ + __u32 fd; /* out: device handle */ + __u32 flags; /* in: KVM_CREATE_DEVICE_xxx */ +}; + +4.80 KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR + +Capability: KVM_CAP_DEVICE_CTRL, KVM_CAP_VM_ATTRIBUTES for vm device, + KVM_CAP_VCPU_ATTRIBUTES for vcpu device +Type: device ioctl, vm ioctl, vcpu ioctl +Parameters: struct kvm_device_attr +Returns: 0 on success, -1 on error +Errors: + ENXIO: The group or attribute is unknown/unsupported for this device + or hardware support is missing. + EPERM: The attribute cannot (currently) be accessed this way + (e.g. read-only attribute, or attribute that only makes + sense when the device is in a different state) + + Other error conditions may be defined by individual device types. + +Gets/sets a specified piece of device configuration and/or state. The +semantics are device-specific. See individual device documentation in +the "devices" directory. As with ONE_REG, the size of the data +transferred is defined by the particular attribute. + +struct kvm_device_attr { + __u32 flags; /* no flags currently defined */ + __u32 group; /* device-defined */ + __u64 attr; /* group-defined */ + __u64 addr; /* userspace address of attr data */ +}; + +4.81 KVM_HAS_DEVICE_ATTR + +Capability: KVM_CAP_DEVICE_CTRL, KVM_CAP_VM_ATTRIBUTES for vm device, + KVM_CAP_VCPU_ATTRIBUTES for vcpu device +Type: device ioctl, vm ioctl, vcpu ioctl +Parameters: struct kvm_device_attr +Returns: 0 on success, -1 on error +Errors: + ENXIO: The group or attribute is unknown/unsupported for this device + or hardware support is missing. + +Tests whether a device supports a particular attribute. A successful +return indicates the attribute is implemented. It does not necessarily +indicate that the attribute can be read or written in the device's +current state. "addr" is ignored. + +4.82 KVM_ARM_VCPU_INIT + +Capability: basic +Architectures: arm, arm64 +Type: vcpu ioctl +Parameters: struct kvm_vcpu_init (in) +Returns: 0 on success; -1 on error +Errors: + Â EINVAL: Â Â Â the target is unknown, or the combination of features is invalid. + Â ENOENT: Â Â Â a features bit specified is unknown. + +This tells KVM what type of CPU to present to the guest, and what +optional features it should have. Â This will cause a reset of the cpu +registers to their initial values. Â If this is not called, KVM_RUN will +return ENOEXEC for that vcpu. + +Note that because some registers reflect machine topology, all vcpus +should be created before this ioctl is invoked. + +Userspace can call this function multiple times for a given vcpu, including +after the vcpu has been run. This will reset the vcpu to its initial +state. All calls to this function after the initial call must use the same +target and same set of feature flags, otherwise EINVAL will be returned. + +Possible features: + - KVM_ARM_VCPU_POWER_OFF: Starts the CPU in a power-off state. + Depends on KVM_CAP_ARM_PSCI. If not set, the CPU will be powered on + and execute guest code when KVM_RUN is called. + - KVM_ARM_VCPU_EL1_32BIT: Starts the CPU in a 32bit mode. + Depends on KVM_CAP_ARM_EL1_32BIT (arm64 only). + - KVM_ARM_VCPU_PSCI_0_2: Emulate PSCI v0.2 (or a future revision + backward compatible with v0.2) for the CPU. + Depends on KVM_CAP_ARM_PSCI_0_2. + - KVM_ARM_VCPU_PMU_V3: Emulate PMUv3 for the CPU. + Depends on KVM_CAP_ARM_PMU_V3. + + - KVM_ARM_VCPU_PTRAUTH_ADDRESS: Enables Address Pointer authentication + for arm64 only. + Depends on KVM_CAP_ARM_PTRAUTH_ADDRESS. + If KVM_CAP_ARM_PTRAUTH_ADDRESS and KVM_CAP_ARM_PTRAUTH_GENERIC are + both present, then both KVM_ARM_VCPU_PTRAUTH_ADDRESS and + KVM_ARM_VCPU_PTRAUTH_GENERIC must be requested or neither must be + requested. + + - KVM_ARM_VCPU_PTRAUTH_GENERIC: Enables Generic Pointer authentication + for arm64 only. + Depends on KVM_CAP_ARM_PTRAUTH_GENERIC. + If KVM_CAP_ARM_PTRAUTH_ADDRESS and KVM_CAP_ARM_PTRAUTH_GENERIC are + both present, then both KVM_ARM_VCPU_PTRAUTH_ADDRESS and + KVM_ARM_VCPU_PTRAUTH_GENERIC must be requested or neither must be + requested. + + - KVM_ARM_VCPU_SVE: Enables SVE for the CPU (arm64 only). + Depends on KVM_CAP_ARM_SVE. + Requires KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE): + + * After KVM_ARM_VCPU_INIT: + + - KVM_REG_ARM64_SVE_VLS may be read using KVM_GET_ONE_REG: the + initial value of this pseudo-register indicates the best set of + vector lengths possible for a vcpu on this host. + + * Before KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE): + + - KVM_RUN and KVM_GET_REG_LIST are not available; + + - KVM_GET_ONE_REG and KVM_SET_ONE_REG cannot be used to access + the scalable archietctural SVE registers + KVM_REG_ARM64_SVE_ZREG(), KVM_REG_ARM64_SVE_PREG() or + KVM_REG_ARM64_SVE_FFR; + + - KVM_REG_ARM64_SVE_VLS may optionally be written using + KVM_SET_ONE_REG, to modify the set of vector lengths available + for the vcpu. + + * After KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE): + + - the KVM_REG_ARM64_SVE_VLS pseudo-register is immutable, and can + no longer be written using KVM_SET_ONE_REG. + +4.83 KVM_ARM_PREFERRED_TARGET + +Capability: basic +Architectures: arm, arm64 +Type: vm ioctl +Parameters: struct struct kvm_vcpu_init (out) +Returns: 0 on success; -1 on error +Errors: + ENODEV: no preferred target available for the host + +This queries KVM for preferred CPU target type which can be emulated +by KVM on underlying host. + +The ioctl returns struct kvm_vcpu_init instance containing information +about preferred CPU target type and recommended features for it. The +kvm_vcpu_init->features bitmap returned will have feature bits set if +the preferred target recommends setting these features, but this is +not mandatory. + +The information returned by this ioctl can be used to prepare an instance +of struct kvm_vcpu_init for KVM_ARM_VCPU_INIT ioctl which will result in +in VCPU matching underlying host. + + +4.84 KVM_GET_REG_LIST + +Capability: basic +Architectures: arm, arm64, mips +Type: vcpu ioctl +Parameters: struct kvm_reg_list (in/out) +Returns: 0 on success; -1 on error +Errors: + Â E2BIG: Â Â Â Â the reg index list is too big to fit in the array specified by + Â Â Â Â Â Â Â Â Â Â Â Â the user (the number required will be written into n). + +struct kvm_reg_list { + __u64 n; /* number of registers in reg[] */ + __u64 reg[0]; +}; + +This ioctl returns the guest registers that are supported for the +KVM_GET_ONE_REG/KVM_SET_ONE_REG calls. + + +4.85 KVM_ARM_SET_DEVICE_ADDR (deprecated) + +Capability: KVM_CAP_ARM_SET_DEVICE_ADDR +Architectures: arm, arm64 +Type: vm ioctl +Parameters: struct kvm_arm_device_address (in) +Returns: 0 on success, -1 on error +Errors: + ENODEV: The device id is unknown + ENXIO: Device not supported on current system + EEXIST: Address already set + E2BIG: Address outside guest physical address space + EBUSY: Address overlaps with other device range + +struct kvm_arm_device_addr { + __u64 id; + __u64 addr; +}; + +Specify a device address in the guest's physical address space where guests +can access emulated or directly exposed devices, which the host kernel needs +to know about. The id field is an architecture specific identifier for a +specific device. + +ARM/arm64 divides the id field into two parts, a device id and an +address type id specific to the individual device. + + Â bits: | 63 ... 32 | 31 ... 16 | 15 ... 0 | + field: | 0x00000000 | device id | addr type id | + +ARM/arm64 currently only require this when using the in-kernel GIC +support for the hardware VGIC features, using KVM_ARM_DEVICE_VGIC_V2 +as the device id. When setting the base address for the guest's +mapping of the VGIC virtual CPU and distributor interface, the ioctl +must be called after calling KVM_CREATE_IRQCHIP, but before calling +KVM_RUN on any of the VCPUs. Calling this ioctl twice for any of the +base addresses will return -EEXIST. + +Note, this IOCTL is deprecated and the more flexible SET/GET_DEVICE_ATTR API +should be used instead. + + +4.86 KVM_PPC_RTAS_DEFINE_TOKEN + +Capability: KVM_CAP_PPC_RTAS +Architectures: ppc +Type: vm ioctl +Parameters: struct kvm_rtas_token_args +Returns: 0 on success, -1 on error + +Defines a token value for a RTAS (Run Time Abstraction Services) +service in order to allow it to be handled in the kernel. The +argument struct gives the name of the service, which must be the name +of a service that has a kernel-side implementation. If the token +value is non-zero, it will be associated with that service, and +subsequent RTAS calls by the guest specifying that token will be +handled by the kernel. If the token value is 0, then any token +associated with the service will be forgotten, and subsequent RTAS +calls by the guest for that service will be passed to userspace to be +handled. + +4.87 KVM_SET_GUEST_DEBUG + +Capability: KVM_CAP_SET_GUEST_DEBUG +Architectures: x86, s390, ppc, arm64 +Type: vcpu ioctl +Parameters: struct kvm_guest_debug (in) +Returns: 0 on success; -1 on error + +struct kvm_guest_debug { + __u32 control; + __u32 pad; + struct kvm_guest_debug_arch arch; +}; + +Set up the processor specific debug registers and configure vcpu for +handling guest debug events. There are two parts to the structure, the +first a control bitfield indicates the type of debug events to handle +when running. Common control bits are: + + - KVM_GUESTDBG_ENABLE: guest debugging is enabled + - KVM_GUESTDBG_SINGLESTEP: the next run should single-step + +The top 16 bits of the control field are architecture specific control +flags which can include the following: + + - KVM_GUESTDBG_USE_SW_BP: using software breakpoints [x86, arm64] + - KVM_GUESTDBG_USE_HW_BP: using hardware breakpoints [x86, s390, arm64] + - KVM_GUESTDBG_INJECT_DB: inject DB type exception [x86] + - KVM_GUESTDBG_INJECT_BP: inject BP type exception [x86] + - KVM_GUESTDBG_EXIT_PENDING: trigger an immediate guest exit [s390] + +For example KVM_GUESTDBG_USE_SW_BP indicates that software breakpoints +are enabled in memory so we need to ensure breakpoint exceptions are +correctly trapped and the KVM run loop exits at the breakpoint and not +running off into the normal guest vector. For KVM_GUESTDBG_USE_HW_BP +we need to ensure the guest vCPUs architecture specific registers are +updated to the correct (supplied) values. + +The second part of the structure is architecture specific and +typically contains a set of debug registers. + +For arm64 the number of debug registers is implementation defined and +can be determined by querying the KVM_CAP_GUEST_DEBUG_HW_BPS and +KVM_CAP_GUEST_DEBUG_HW_WPS capabilities which return a positive number +indicating the number of supported registers. + +When debug events exit the main run loop with the reason +KVM_EXIT_DEBUG with the kvm_debug_exit_arch part of the kvm_run +structure containing architecture specific debug information. + +4.88 KVM_GET_EMULATED_CPUID + +Capability: KVM_CAP_EXT_EMUL_CPUID +Architectures: x86 +Type: system ioctl +Parameters: struct kvm_cpuid2 (in/out) +Returns: 0 on success, -1 on error + +struct kvm_cpuid2 { + __u32 nent; + __u32 flags; + struct kvm_cpuid_entry2 entries[0]; +}; + +The member 'flags' is used for passing flags from userspace. + +#define KVM_CPUID_FLAG_SIGNIFCANT_INDEX BIT(0) +#define KVM_CPUID_FLAG_STATEFUL_FUNC BIT(1) +#define KVM_CPUID_FLAG_STATE_READ_NEXT BIT(2) + +struct kvm_cpuid_entry2 { + __u32 function; + __u32 index; + __u32 flags; + __u32 eax; + __u32 ebx; + __u32 ecx; + __u32 edx; + __u32 padding[3]; +}; + +This ioctl returns x86 cpuid features which are emulated by +kvm.Userspace can use the information returned by this ioctl to query +which features are emulated by kvm instead of being present natively. + +Userspace invokes KVM_GET_EMULATED_CPUID by passing a kvm_cpuid2 +structure with the 'nent' field indicating the number of entries in +the variable-size array 'entries'. If the number of entries is too low +to describe the cpu capabilities, an error (E2BIG) is returned. If the +number is too high, the 'nent' field is adjusted and an error (ENOMEM) +is returned. If the number is just right, the 'nent' field is adjusted +to the number of valid entries in the 'entries' array, which is then +filled. + +The entries returned are the set CPUID bits of the respective features +which kvm emulates, as returned by the CPUID instruction, with unknown +or unsupported feature bits cleared. + +Features like x2apic, for example, may not be present in the host cpu +but are exposed by kvm in KVM_GET_SUPPORTED_CPUID because they can be +emulated efficiently and thus not included here. + +The fields in each entry are defined as follows: + + function: the eax value used to obtain the entry + index: the ecx value used to obtain the entry (for entries that are + affected by ecx) + flags: an OR of zero or more of the following: + KVM_CPUID_FLAG_SIGNIFCANT_INDEX: + if the index field is valid + KVM_CPUID_FLAG_STATEFUL_FUNC: + if cpuid for this function returns different values for successive + invocations; there will be several entries with the same function, + all with this flag set + KVM_CPUID_FLAG_STATE_READ_NEXT: + for KVM_CPUID_FLAG_STATEFUL_FUNC entries, set if this entry is + the first entry to be read by a cpu + eax, ebx, ecx, edx: the values returned by the cpuid instruction for + this function/index combination + +4.89 KVM_S390_MEM_OP + +Capability: KVM_CAP_S390_MEM_OP +Architectures: s390 +Type: vcpu ioctl +Parameters: struct kvm_s390_mem_op (in) +Returns: = 0 on success, + < 0 on generic error (e.g. -EFAULT or -ENOMEM), + > 0 if an exception occurred while walking the page tables + +Read or write data from/to the logical (virtual) memory of a VCPU. + +Parameters are specified via the following structure: + +struct kvm_s390_mem_op { + __u64 gaddr; /* the guest address */ + __u64 flags; /* flags */ + __u32 size; /* amount of bytes */ + __u32 op; /* type of operation */ + __u64 buf; /* buffer in userspace */ + __u8 ar; /* the access register number */ + __u8 reserved[31]; /* should be set to 0 */ +}; + +The type of operation is specified in the "op" field. It is either +KVM_S390_MEMOP_LOGICAL_READ for reading from logical memory space or +KVM_S390_MEMOP_LOGICAL_WRITE for writing to logical memory space. The +KVM_S390_MEMOP_F_CHECK_ONLY flag can be set in the "flags" field to check +whether the corresponding memory access would create an access exception +(without touching the data in the memory at the destination). In case an +access exception occurred while walking the MMU tables of the guest, the +ioctl returns a positive error number to indicate the type of exception. +This exception is also raised directly at the corresponding VCPU if the +flag KVM_S390_MEMOP_F_INJECT_EXCEPTION is set in the "flags" field. + +The start address of the memory region has to be specified in the "gaddr" +field, and the length of the region in the "size" field. "buf" is the buffer +supplied by the userspace application where the read data should be written +to for KVM_S390_MEMOP_LOGICAL_READ, or where the data that should be written +is stored for a KVM_S390_MEMOP_LOGICAL_WRITE. "buf" is unused and can be NULL +when KVM_S390_MEMOP_F_CHECK_ONLY is specified. "ar" designates the access +register number to be used. + +The "reserved" field is meant for future extensions. It is not used by +KVM with the currently defined set of flags. + +4.90 KVM_S390_GET_SKEYS + +Capability: KVM_CAP_S390_SKEYS +Architectures: s390 +Type: vm ioctl +Parameters: struct kvm_s390_skeys +Returns: 0 on success, KVM_S390_GET_KEYS_NONE if guest is not using storage + keys, negative value on error + +This ioctl is used to get guest storage key values on the s390 +architecture. The ioctl takes parameters via the kvm_s390_skeys struct. + +struct kvm_s390_skeys { + __u64 start_gfn; + __u64 count; + __u64 skeydata_addr; + __u32 flags; + __u32 reserved[9]; +}; + +The start_gfn field is the number of the first guest frame whose storage keys +you want to get. + +The count field is the number of consecutive frames (starting from start_gfn) +whose storage keys to get. The count field must be at least 1 and the maximum +allowed value is defined as KVM_S390_SKEYS_ALLOC_MAX. Values outside this range +will cause the ioctl to return -EINVAL. + +The skeydata_addr field is the address to a buffer large enough to hold count +bytes. This buffer will be filled with storage key data by the ioctl. + +4.91 KVM_S390_SET_SKEYS + +Capability: KVM_CAP_S390_SKEYS +Architectures: s390 +Type: vm ioctl +Parameters: struct kvm_s390_skeys +Returns: 0 on success, negative value on error + +This ioctl is used to set guest storage key values on the s390 +architecture. The ioctl takes parameters via the kvm_s390_skeys struct. +See section on KVM_S390_GET_SKEYS for struct definition. + +The start_gfn field is the number of the first guest frame whose storage keys +you want to set. + +The count field is the number of consecutive frames (starting from start_gfn) +whose storage keys to get. The count field must be at least 1 and the maximum +allowed value is defined as KVM_S390_SKEYS_ALLOC_MAX. Values outside this range +will cause the ioctl to return -EINVAL. + +The skeydata_addr field is the address to a buffer containing count bytes of +storage keys. Each byte in the buffer will be set as the storage key for a +single frame starting at start_gfn for count frames. + +Note: If any architecturally invalid key value is found in the given data then +the ioctl will return -EINVAL. + +4.92 KVM_S390_IRQ + +Capability: KVM_CAP_S390_INJECT_IRQ +Architectures: s390 +Type: vcpu ioctl +Parameters: struct kvm_s390_irq (in) +Returns: 0 on success, -1 on error +Errors: + EINVAL: interrupt type is invalid + type is KVM_S390_SIGP_STOP and flag parameter is invalid value + type is KVM_S390_INT_EXTERNAL_CALL and code is bigger + than the maximum of VCPUs + EBUSY: type is KVM_S390_SIGP_SET_PREFIX and vcpu is not stopped + type is KVM_S390_SIGP_STOP and a stop irq is already pending + type is KVM_S390_INT_EXTERNAL_CALL and an external call interrupt + is already pending + +Allows to inject an interrupt to the guest. + +Using struct kvm_s390_irq as a parameter allows +to inject additional payload which is not +possible via KVM_S390_INTERRUPT. + +Interrupt parameters are passed via kvm_s390_irq: + +struct kvm_s390_irq { + __u64 type; + union { + struct kvm_s390_io_info io; + struct kvm_s390_ext_info ext; + struct kvm_s390_pgm_info pgm; + struct kvm_s390_emerg_info emerg; + struct kvm_s390_extcall_info extcall; + struct kvm_s390_prefix_info prefix; + struct kvm_s390_stop_info stop; + struct kvm_s390_mchk_info mchk; + char reserved[64]; + } u; +}; + +type can be one of the following: + +KVM_S390_SIGP_STOP - sigp stop; parameter in .stop +KVM_S390_PROGRAM_INT - program check; parameters in .pgm +KVM_S390_SIGP_SET_PREFIX - sigp set prefix; parameters in .prefix +KVM_S390_RESTART - restart; no parameters +KVM_S390_INT_CLOCK_COMP - clock comparator interrupt; no parameters +KVM_S390_INT_CPU_TIMER - CPU timer interrupt; no parameters +KVM_S390_INT_EMERGENCY - sigp emergency; parameters in .emerg +KVM_S390_INT_EXTERNAL_CALL - sigp external call; parameters in .extcall +KVM_S390_MCHK - machine check interrupt; parameters in .mchk + +This is an asynchronous vcpu ioctl and can be invoked from any thread. + +4.94 KVM_S390_GET_IRQ_STATE + +Capability: KVM_CAP_S390_IRQ_STATE +Architectures: s390 +Type: vcpu ioctl +Parameters: struct kvm_s390_irq_state (out) +Returns: >= number of bytes copied into buffer, + -EINVAL if buffer size is 0, + -ENOBUFS if buffer size is too small to fit all pending interrupts, + -EFAULT if the buffer address was invalid + +This ioctl allows userspace to retrieve the complete state of all currently +pending interrupts in a single buffer. Use cases include migration +and introspection. The parameter structure contains the address of a +userspace buffer and its length: + +struct kvm_s390_irq_state { + __u64 buf; + __u32 flags; /* will stay unused for compatibility reasons */ + __u32 len; + __u32 reserved[4]; /* will stay unused for compatibility reasons */ +}; + +Userspace passes in the above struct and for each pending interrupt a +struct kvm_s390_irq is copied to the provided buffer. + +The structure contains a flags and a reserved field for future extensions. As +the kernel never checked for flags == 0 and QEMU never pre-zeroed flags and +reserved, these fields can not be used in the future without breaking +compatibility. + +If -ENOBUFS is returned the buffer provided was too small and userspace +may retry with a bigger buffer. + +4.95 KVM_S390_SET_IRQ_STATE + +Capability: KVM_CAP_S390_IRQ_STATE +Architectures: s390 +Type: vcpu ioctl +Parameters: struct kvm_s390_irq_state (in) +Returns: 0 on success, + -EFAULT if the buffer address was invalid, + -EINVAL for an invalid buffer length (see below), + -EBUSY if there were already interrupts pending, + errors occurring when actually injecting the + interrupt. See KVM_S390_IRQ. + +This ioctl allows userspace to set the complete state of all cpu-local +interrupts currently pending for the vcpu. It is intended for restoring +interrupt state after a migration. The input parameter is a userspace buffer +containing a struct kvm_s390_irq_state: + +struct kvm_s390_irq_state { + __u64 buf; + __u32 flags; /* will stay unused for compatibility reasons */ + __u32 len; + __u32 reserved[4]; /* will stay unused for compatibility reasons */ +}; + +The restrictions for flags and reserved apply as well. +(see KVM_S390_GET_IRQ_STATE) + +The userspace memory referenced by buf contains a struct kvm_s390_irq +for each interrupt to be injected into the guest. +If one of the interrupts could not be injected for some reason the +ioctl aborts. + +len must be a multiple of sizeof(struct kvm_s390_irq). It must be > 0 +and it must not exceed (max_vcpus + 32) * sizeof(struct kvm_s390_irq), +which is the maximum number of possibly pending cpu-local interrupts. + +4.96 KVM_SMI + +Capability: KVM_CAP_X86_SMM +Architectures: x86 +Type: vcpu ioctl +Parameters: none +Returns: 0 on success, -1 on error + +Queues an SMI on the thread's vcpu. + +4.97 KVM_CAP_PPC_MULTITCE + +Capability: KVM_CAP_PPC_MULTITCE +Architectures: ppc +Type: vm + +This capability means the kernel is capable of handling hypercalls +H_PUT_TCE_INDIRECT and H_STUFF_TCE without passing those into the user +space. This significantly accelerates DMA operations for PPC KVM guests. +User space should expect that its handlers for these hypercalls +are not going to be called if user space previously registered LIOBN +in KVM (via KVM_CREATE_SPAPR_TCE or similar calls). + +In order to enable H_PUT_TCE_INDIRECT and H_STUFF_TCE use in the guest, +user space might have to advertise it for the guest. For example, +IBM pSeries (sPAPR) guest starts using them if "hcall-multi-tce" is +present in the "ibm,hypertas-functions" device-tree property. + +The hypercalls mentioned above may or may not be processed successfully +in the kernel based fast path. If they can not be handled by the kernel, +they will get passed on to user space. So user space still has to have +an implementation for these despite the in kernel acceleration. + +This capability is always enabled. + +4.98 KVM_CREATE_SPAPR_TCE_64 + +Capability: KVM_CAP_SPAPR_TCE_64 +Architectures: powerpc +Type: vm ioctl +Parameters: struct kvm_create_spapr_tce_64 (in) +Returns: file descriptor for manipulating the created TCE table + +This is an extension for KVM_CAP_SPAPR_TCE which only supports 32bit +windows, described in 4.62 KVM_CREATE_SPAPR_TCE + +This capability uses extended struct in ioctl interface: + +/* for KVM_CAP_SPAPR_TCE_64 */ +struct kvm_create_spapr_tce_64 { + __u64 liobn; + __u32 page_shift; + __u32 flags; + __u64 offset; /* in pages */ + __u64 size; /* in pages */ +}; + +The aim of extension is to support an additional bigger DMA window with +a variable page size. +KVM_CREATE_SPAPR_TCE_64 receives a 64bit window size, an IOMMU page shift and +a bus offset of the corresponding DMA window, @size and @offset are numbers +of IOMMU pages. + +@flags are not used at the moment. + +The rest of functionality is identical to KVM_CREATE_SPAPR_TCE. + +4.99 KVM_REINJECT_CONTROL + +Capability: KVM_CAP_REINJECT_CONTROL +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_reinject_control (in) +Returns: 0 on success, + -EFAULT if struct kvm_reinject_control cannot be read, + -ENXIO if KVM_CREATE_PIT or KVM_CREATE_PIT2 didn't succeed earlier. + +i8254 (PIT) has two modes, reinject and !reinject. The default is reinject, +where KVM queues elapsed i8254 ticks and monitors completion of interrupt from +vector(s) that i8254 injects. Reinject mode dequeues a tick and injects its +interrupt whenever there isn't a pending interrupt from i8254. +!reinject mode injects an interrupt as soon as a tick arrives. + +struct kvm_reinject_control { + __u8 pit_reinject; + __u8 reserved[31]; +}; + +pit_reinject = 0 (!reinject mode) is recommended, unless running an old +operating system that uses the PIT for timing (e.g. Linux 2.4.x). + +4.100 KVM_PPC_CONFIGURE_V3_MMU + +Capability: KVM_CAP_PPC_RADIX_MMU or KVM_CAP_PPC_HASH_MMU_V3 +Architectures: ppc +Type: vm ioctl +Parameters: struct kvm_ppc_mmuv3_cfg (in) +Returns: 0 on success, + -EFAULT if struct kvm_ppc_mmuv3_cfg cannot be read, + -EINVAL if the configuration is invalid + +This ioctl controls whether the guest will use radix or HPT (hashed +page table) translation, and sets the pointer to the process table for +the guest. + +struct kvm_ppc_mmuv3_cfg { + __u64 flags; + __u64 process_table; +}; + +There are two bits that can be set in flags; KVM_PPC_MMUV3_RADIX and +KVM_PPC_MMUV3_GTSE. KVM_PPC_MMUV3_RADIX, if set, configures the guest +to use radix tree translation, and if clear, to use HPT translation. +KVM_PPC_MMUV3_GTSE, if set and if KVM permits it, configures the guest +to be able to use the global TLB and SLB invalidation instructions; +if clear, the guest may not use these instructions. + +The process_table field specifies the address and size of the guest +process table, which is in the guest's space. This field is formatted +as the second doubleword of the partition table entry, as defined in +the Power ISA V3.00, Book III section 5.7.6.1. + +4.101 KVM_PPC_GET_RMMU_INFO + +Capability: KVM_CAP_PPC_RADIX_MMU +Architectures: ppc +Type: vm ioctl +Parameters: struct kvm_ppc_rmmu_info (out) +Returns: 0 on success, + -EFAULT if struct kvm_ppc_rmmu_info cannot be written, + -EINVAL if no useful information can be returned + +This ioctl returns a structure containing two things: (a) a list +containing supported radix tree geometries, and (b) a list that maps +page sizes to put in the "AP" (actual page size) field for the tlbie +(TLB invalidate entry) instruction. + +struct kvm_ppc_rmmu_info { + struct kvm_ppc_radix_geom { + __u8 page_shift; + __u8 level_bits[4]; + __u8 pad[3]; + } geometries[8]; + __u32 ap_encodings[8]; +}; + +The geometries[] field gives up to 8 supported geometries for the +radix page table, in terms of the log base 2 of the smallest page +size, and the number of bits indexed at each level of the tree, from +the PTE level up to the PGD level in that order. Any unused entries +will have 0 in the page_shift field. + +The ap_encodings gives the supported page sizes and their AP field +encodings, encoded with the AP value in the top 3 bits and the log +base 2 of the page size in the bottom 6 bits. + +4.102 KVM_PPC_RESIZE_HPT_PREPARE + +Capability: KVM_CAP_SPAPR_RESIZE_HPT +Architectures: powerpc +Type: vm ioctl +Parameters: struct kvm_ppc_resize_hpt (in) +Returns: 0 on successful completion, + >0 if a new HPT is being prepared, the value is an estimated + number of milliseconds until preparation is complete + -EFAULT if struct kvm_reinject_control cannot be read, + -EINVAL if the supplied shift or flags are invalid + -ENOMEM if unable to allocate the new HPT + -ENOSPC if there was a hash collision when moving existing + HPT entries to the new HPT + -EIO on other error conditions + +Used to implement the PAPR extension for runtime resizing of a guest's +Hashed Page Table (HPT). Specifically this starts, stops or monitors +the preparation of a new potential HPT for the guest, essentially +implementing the H_RESIZE_HPT_PREPARE hypercall. + +If called with shift > 0 when there is no pending HPT for the guest, +this begins preparation of a new pending HPT of size 2^(shift) bytes. +It then returns a positive integer with the estimated number of +milliseconds until preparation is complete. + +If called when there is a pending HPT whose size does not match that +requested in the parameters, discards the existing pending HPT and +creates a new one as above. + +If called when there is a pending HPT of the size requested, will: + * If preparation of the pending HPT is already complete, return 0 + * If preparation of the pending HPT has failed, return an error + code, then discard the pending HPT. + * If preparation of the pending HPT is still in progress, return an + estimated number of milliseconds until preparation is complete. + +If called with shift == 0, discards any currently pending HPT and +returns 0 (i.e. cancels any in-progress preparation). + +flags is reserved for future expansion, currently setting any bits in +flags will result in an -EINVAL. + +Normally this will be called repeatedly with the same parameters until +it returns <= 0. The first call will initiate preparation, subsequent +ones will monitor preparation until it completes or fails. + +struct kvm_ppc_resize_hpt { + __u64 flags; + __u32 shift; + __u32 pad; +}; + +4.103 KVM_PPC_RESIZE_HPT_COMMIT + +Capability: KVM_CAP_SPAPR_RESIZE_HPT +Architectures: powerpc +Type: vm ioctl +Parameters: struct kvm_ppc_resize_hpt (in) +Returns: 0 on successful completion, + -EFAULT if struct kvm_reinject_control cannot be read, + -EINVAL if the supplied shift or flags are invalid + -ENXIO is there is no pending HPT, or the pending HPT doesn't + have the requested size + -EBUSY if the pending HPT is not fully prepared + -ENOSPC if there was a hash collision when moving existing + HPT entries to the new HPT + -EIO on other error conditions + +Used to implement the PAPR extension for runtime resizing of a guest's +Hashed Page Table (HPT). Specifically this requests that the guest be +transferred to working with the new HPT, essentially implementing the +H_RESIZE_HPT_COMMIT hypercall. + +This should only be called after KVM_PPC_RESIZE_HPT_PREPARE has +returned 0 with the same parameters. In other cases +KVM_PPC_RESIZE_HPT_COMMIT will return an error (usually -ENXIO or +-EBUSY, though others may be possible if the preparation was started, +but failed). + +This will have undefined effects on the guest if it has not already +placed itself in a quiescent state where no vcpu will make MMU enabled +memory accesses. + +On succsful completion, the pending HPT will become the guest's active +HPT and the previous HPT will be discarded. + +On failure, the guest will still be operating on its previous HPT. + +struct kvm_ppc_resize_hpt { + __u64 flags; + __u32 shift; + __u32 pad; +}; + +4.104 KVM_X86_GET_MCE_CAP_SUPPORTED + +Capability: KVM_CAP_MCE +Architectures: x86 +Type: system ioctl +Parameters: u64 mce_cap (out) +Returns: 0 on success, -1 on error + +Returns supported MCE capabilities. The u64 mce_cap parameter +has the same format as the MSR_IA32_MCG_CAP register. Supported +capabilities will have the corresponding bits set. + +4.105 KVM_X86_SETUP_MCE + +Capability: KVM_CAP_MCE +Architectures: x86 +Type: vcpu ioctl +Parameters: u64 mcg_cap (in) +Returns: 0 on success, + -EFAULT if u64 mcg_cap cannot be read, + -EINVAL if the requested number of banks is invalid, + -EINVAL if requested MCE capability is not supported. + +Initializes MCE support for use. The u64 mcg_cap parameter +has the same format as the MSR_IA32_MCG_CAP register and +specifies which capabilities should be enabled. The maximum +supported number of error-reporting banks can be retrieved when +checking for KVM_CAP_MCE. The supported capabilities can be +retrieved with KVM_X86_GET_MCE_CAP_SUPPORTED. + +4.106 KVM_X86_SET_MCE + +Capability: KVM_CAP_MCE +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_x86_mce (in) +Returns: 0 on success, + -EFAULT if struct kvm_x86_mce cannot be read, + -EINVAL if the bank number is invalid, + -EINVAL if VAL bit is not set in status field. + +Inject a machine check error (MCE) into the guest. The input +parameter is: + +struct kvm_x86_mce { + __u64 status; + __u64 addr; + __u64 misc; + __u64 mcg_status; + __u8 bank; + __u8 pad1[7]; + __u64 pad2[3]; +}; + +If the MCE being reported is an uncorrected error, KVM will +inject it as an MCE exception into the guest. If the guest +MCG_STATUS register reports that an MCE is in progress, KVM +causes an KVM_EXIT_SHUTDOWN vmexit. + +Otherwise, if the MCE is a corrected error, KVM will just +store it in the corresponding bank (provided this bank is +not holding a previously reported uncorrected error). + +4.107 KVM_S390_GET_CMMA_BITS + +Capability: KVM_CAP_S390_CMMA_MIGRATION +Architectures: s390 +Type: vm ioctl +Parameters: struct kvm_s390_cmma_log (in, out) +Returns: 0 on success, a negative value on error + +This ioctl is used to get the values of the CMMA bits on the s390 +architecture. It is meant to be used in two scenarios: +- During live migration to save the CMMA values. Live migration needs + to be enabled via the KVM_REQ_START_MIGRATION VM property. +- To non-destructively peek at the CMMA values, with the flag + KVM_S390_CMMA_PEEK set. + +The ioctl takes parameters via the kvm_s390_cmma_log struct. The desired +values are written to a buffer whose location is indicated via the "values" +member in the kvm_s390_cmma_log struct. The values in the input struct are +also updated as needed. +Each CMMA value takes up one byte. + +struct kvm_s390_cmma_log { + __u64 start_gfn; + __u32 count; + __u32 flags; + union { + __u64 remaining; + __u64 mask; + }; + __u64 values; +}; + +start_gfn is the number of the first guest frame whose CMMA values are +to be retrieved, + +count is the length of the buffer in bytes, + +values points to the buffer where the result will be written to. + +If count is greater than KVM_S390_SKEYS_MAX, then it is considered to be +KVM_S390_SKEYS_MAX. KVM_S390_SKEYS_MAX is re-used for consistency with +other ioctls. + +The result is written in the buffer pointed to by the field values, and +the values of the input parameter are updated as follows. + +Depending on the flags, different actions are performed. The only +supported flag so far is KVM_S390_CMMA_PEEK. + +The default behaviour if KVM_S390_CMMA_PEEK is not set is: +start_gfn will indicate the first page frame whose CMMA bits were dirty. +It is not necessarily the same as the one passed as input, as clean pages +are skipped. + +count will indicate the number of bytes actually written in the buffer. +It can (and very often will) be smaller than the input value, since the +buffer is only filled until 16 bytes of clean values are found (which +are then not copied in the buffer). Since a CMMA migration block needs +the base address and the length, for a total of 16 bytes, we will send +back some clean data if there is some dirty data afterwards, as long as +the size of the clean data does not exceed the size of the header. This +allows to minimize the amount of data to be saved or transferred over +the network at the expense of more roundtrips to userspace. The next +invocation of the ioctl will skip over all the clean values, saving +potentially more than just the 16 bytes we found. + +If KVM_S390_CMMA_PEEK is set: +the existing storage attributes are read even when not in migration +mode, and no other action is performed; + +the output start_gfn will be equal to the input start_gfn, + +the output count will be equal to the input count, except if the end of +memory has been reached. + +In both cases: +the field "remaining" will indicate the total number of dirty CMMA values +still remaining, or 0 if KVM_S390_CMMA_PEEK is set and migration mode is +not enabled. + +mask is unused. + +values points to the userspace buffer where the result will be stored. + +This ioctl can fail with -ENOMEM if not enough memory can be allocated to +complete the task, with -ENXIO if CMMA is not enabled, with -EINVAL if +KVM_S390_CMMA_PEEK is not set but migration mode was not enabled, with +-EFAULT if the userspace address is invalid or if no page table is +present for the addresses (e.g. when using hugepages). + +4.108 KVM_S390_SET_CMMA_BITS + +Capability: KVM_CAP_S390_CMMA_MIGRATION +Architectures: s390 +Type: vm ioctl +Parameters: struct kvm_s390_cmma_log (in) +Returns: 0 on success, a negative value on error + +This ioctl is used to set the values of the CMMA bits on the s390 +architecture. It is meant to be used during live migration to restore +the CMMA values, but there are no restrictions on its use. +The ioctl takes parameters via the kvm_s390_cmma_values struct. +Each CMMA value takes up one byte. + +struct kvm_s390_cmma_log { + __u64 start_gfn; + __u32 count; + __u32 flags; + union { + __u64 remaining; + __u64 mask; + }; + __u64 values; +}; + +start_gfn indicates the starting guest frame number, + +count indicates how many values are to be considered in the buffer, + +flags is not used and must be 0. + +mask indicates which PGSTE bits are to be considered. + +remaining is not used. + +values points to the buffer in userspace where to store the values. + +This ioctl can fail with -ENOMEM if not enough memory can be allocated to +complete the task, with -ENXIO if CMMA is not enabled, with -EINVAL if +the count field is too large (e.g. more than KVM_S390_CMMA_SIZE_MAX) or +if the flags field was not 0, with -EFAULT if the userspace address is +invalid, if invalid pages are written to (e.g. after the end of memory) +or if no page table is present for the addresses (e.g. when using +hugepages). + +4.109 KVM_PPC_GET_CPU_CHAR + +Capability: KVM_CAP_PPC_GET_CPU_CHAR +Architectures: powerpc +Type: vm ioctl +Parameters: struct kvm_ppc_cpu_char (out) +Returns: 0 on successful completion + -EFAULT if struct kvm_ppc_cpu_char cannot be written + +This ioctl gives userspace information about certain characteristics +of the CPU relating to speculative execution of instructions and +possible information leakage resulting from speculative execution (see +CVE-2017-5715, CVE-2017-5753 and CVE-2017-5754). The information is +returned in struct kvm_ppc_cpu_char, which looks like this: + +struct kvm_ppc_cpu_char { + __u64 character; /* characteristics of the CPU */ + __u64 behaviour; /* recommended software behaviour */ + __u64 character_mask; /* valid bits in character */ + __u64 behaviour_mask; /* valid bits in behaviour */ +}; + +For extensibility, the character_mask and behaviour_mask fields +indicate which bits of character and behaviour have been filled in by +the kernel. If the set of defined bits is extended in future then +userspace will be able to tell whether it is running on a kernel that +knows about the new bits. + +The character field describes attributes of the CPU which can help +with preventing inadvertent information disclosure - specifically, +whether there is an instruction to flash-invalidate the L1 data cache +(ori 30,30,0 or mtspr SPRN_TRIG2,rN), whether the L1 data cache is set +to a mode where entries can only be used by the thread that created +them, whether the bcctr[l] instruction prevents speculation, and +whether a speculation barrier instruction (ori 31,31,0) is provided. + +The behaviour field describes actions that software should take to +prevent inadvertent information disclosure, and thus describes which +vulnerabilities the hardware is subject to; specifically whether the +L1 data cache should be flushed when returning to user mode from the +kernel, and whether a speculation barrier should be placed between an +array bounds check and the array access. + +These fields use the same bit definitions as the new +H_GET_CPU_CHARACTERISTICS hypercall. + +4.110 KVM_MEMORY_ENCRYPT_OP + +Capability: basic +Architectures: x86 +Type: system +Parameters: an opaque platform specific structure (in/out) +Returns: 0 on success; -1 on error + +If the platform supports creating encrypted VMs then this ioctl can be used +for issuing platform-specific memory encryption commands to manage those +encrypted VMs. + +Currently, this ioctl is used for issuing Secure Encrypted Virtualization +(SEV) commands on AMD Processors. The SEV commands are defined in +Documentation/virt/kvm/amd-memory-encryption.rst. + +4.111 KVM_MEMORY_ENCRYPT_REG_REGION + +Capability: basic +Architectures: x86 +Type: system +Parameters: struct kvm_enc_region (in) +Returns: 0 on success; -1 on error + +This ioctl can be used to register a guest memory region which may +contain encrypted data (e.g. guest RAM, SMRAM etc). + +It is used in the SEV-enabled guest. When encryption is enabled, a guest +memory region may contain encrypted data. The SEV memory encryption +engine uses a tweak such that two identical plaintext pages, each at +different locations will have differing ciphertexts. So swapping or +moving ciphertext of those pages will not result in plaintext being +swapped. So relocating (or migrating) physical backing pages for the SEV +guest will require some additional steps. + +Note: The current SEV key management spec does not provide commands to +swap or migrate (move) ciphertext pages. Hence, for now we pin the guest +memory region registered with the ioctl. + +4.112 KVM_MEMORY_ENCRYPT_UNREG_REGION + +Capability: basic +Architectures: x86 +Type: system +Parameters: struct kvm_enc_region (in) +Returns: 0 on success; -1 on error + +This ioctl can be used to unregister the guest memory region registered +with KVM_MEMORY_ENCRYPT_REG_REGION ioctl above. + +4.113 KVM_HYPERV_EVENTFD + +Capability: KVM_CAP_HYPERV_EVENTFD +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_hyperv_eventfd (in) + +This ioctl (un)registers an eventfd to receive notifications from the guest on +the specified Hyper-V connection id through the SIGNAL_EVENT hypercall, without +causing a user exit. SIGNAL_EVENT hypercall with non-zero event flag number +(bits 24-31) still triggers a KVM_EXIT_HYPERV_HCALL user exit. + +struct kvm_hyperv_eventfd { + __u32 conn_id; + __s32 fd; + __u32 flags; + __u32 padding[3]; +}; + +The conn_id field should fit within 24 bits: + +#define KVM_HYPERV_CONN_ID_MASK 0x00ffffff + +The acceptable values for the flags field are: + +#define KVM_HYPERV_EVENTFD_DEASSIGN (1 << 0) + +Returns: 0 on success, + -EINVAL if conn_id or flags is outside the allowed range + -ENOENT on deassign if the conn_id isn't registered + -EEXIST on assign if the conn_id is already registered + +4.114 KVM_GET_NESTED_STATE + +Capability: KVM_CAP_NESTED_STATE +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_nested_state (in/out) +Returns: 0 on success, -1 on error +Errors: + E2BIG: the total state size exceeds the value of 'size' specified by + the user; the size required will be written into size. + +struct kvm_nested_state { + __u16 flags; + __u16 format; + __u32 size; + + union { + struct kvm_vmx_nested_state_hdr vmx; + struct kvm_svm_nested_state_hdr svm; + + /* Pad the header to 128 bytes. */ + __u8 pad[120]; + } hdr; + + union { + struct kvm_vmx_nested_state_data vmx[0]; + struct kvm_svm_nested_state_data svm[0]; + } data; +}; + +#define KVM_STATE_NESTED_GUEST_MODE 0x00000001 +#define KVM_STATE_NESTED_RUN_PENDING 0x00000002 +#define KVM_STATE_NESTED_EVMCS 0x00000004 + +#define KVM_STATE_NESTED_FORMAT_VMX 0 +#define KVM_STATE_NESTED_FORMAT_SVM 1 + +#define KVM_STATE_NESTED_VMX_VMCS_SIZE 0x1000 + +#define KVM_STATE_NESTED_VMX_SMM_GUEST_MODE 0x00000001 +#define KVM_STATE_NESTED_VMX_SMM_VMXON 0x00000002 + +struct kvm_vmx_nested_state_hdr { + __u64 vmxon_pa; + __u64 vmcs12_pa; + + struct { + __u16 flags; + } smm; +}; + +struct kvm_vmx_nested_state_data { + __u8 vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE]; + __u8 shadow_vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE]; +}; + +This ioctl copies the vcpu's nested virtualization state from the kernel to +userspace. + +The maximum size of the state can be retrieved by passing KVM_CAP_NESTED_STATE +to the KVM_CHECK_EXTENSION ioctl(). + +4.115 KVM_SET_NESTED_STATE + +Capability: KVM_CAP_NESTED_STATE +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_nested_state (in) +Returns: 0 on success, -1 on error + +This copies the vcpu's kvm_nested_state struct from userspace to the kernel. +For the definition of struct kvm_nested_state, see KVM_GET_NESTED_STATE. + +4.116 KVM_(UN)REGISTER_COALESCED_MMIO + +Capability: KVM_CAP_COALESCED_MMIO (for coalesced mmio) + KVM_CAP_COALESCED_PIO (for coalesced pio) +Architectures: all +Type: vm ioctl +Parameters: struct kvm_coalesced_mmio_zone +Returns: 0 on success, < 0 on error + +Coalesced I/O is a performance optimization that defers hardware +register write emulation so that userspace exits are avoided. It is +typically used to reduce the overhead of emulating frequently accessed +hardware registers. + +When a hardware register is configured for coalesced I/O, write accesses +do not exit to userspace and their value is recorded in a ring buffer +that is shared between kernel and userspace. + +Coalesced I/O is used if one or more write accesses to a hardware +register can be deferred until a read or a write to another hardware +register on the same device. This last access will cause a vmexit and +userspace will process accesses from the ring buffer before emulating +it. That will avoid exiting to userspace on repeated writes. + +Coalesced pio is based on coalesced mmio. There is little difference +between coalesced mmio and pio except that coalesced pio records accesses +to I/O ports. + +4.117 KVM_CLEAR_DIRTY_LOG (vm ioctl) + +Capability: KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 +Architectures: x86, arm, arm64, mips +Type: vm ioctl +Parameters: struct kvm_dirty_log (in) +Returns: 0 on success, -1 on error + +/* for KVM_CLEAR_DIRTY_LOG */ +struct kvm_clear_dirty_log { + __u32 slot; + __u32 num_pages; + __u64 first_page; + union { + void __user *dirty_bitmap; /* one bit per page */ + __u64 padding; + }; +}; + +The ioctl clears the dirty status of pages in a memory slot, according to +the bitmap that is passed in struct kvm_clear_dirty_log's dirty_bitmap +field. Bit 0 of the bitmap corresponds to page "first_page" in the +memory slot, and num_pages is the size in bits of the input bitmap. +first_page must be a multiple of 64; num_pages must also be a multiple of +64 unless first_page + num_pages is the size of the memory slot. For each +bit that is set in the input bitmap, the corresponding page is marked "clean" +in KVM's dirty bitmap, and dirty tracking is re-enabled for that page +(for example via write-protection, or by clearing the dirty bit in +a page table entry). + +If KVM_CAP_MULTI_ADDRESS_SPACE is available, bits 16-31 specifies +the address space for which you want to return the dirty bitmap. +They must be less than the value that KVM_CHECK_EXTENSION returns for +the KVM_CAP_MULTI_ADDRESS_SPACE capability. + +This ioctl is mostly useful when KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 +is enabled; for more information, see the description of the capability. +However, it can always be used as long as KVM_CHECK_EXTENSION confirms +that KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 is present. + +4.118 KVM_GET_SUPPORTED_HV_CPUID + +Capability: KVM_CAP_HYPERV_CPUID +Architectures: x86 +Type: vcpu ioctl +Parameters: struct kvm_cpuid2 (in/out) +Returns: 0 on success, -1 on error + +struct kvm_cpuid2 { + __u32 nent; + __u32 padding; + struct kvm_cpuid_entry2 entries[0]; +}; + +struct kvm_cpuid_entry2 { + __u32 function; + __u32 index; + __u32 flags; + __u32 eax; + __u32 ebx; + __u32 ecx; + __u32 edx; + __u32 padding[3]; +}; + +This ioctl returns x86 cpuid features leaves related to Hyper-V emulation in +KVM. Userspace can use the information returned by this ioctl to construct +cpuid information presented to guests consuming Hyper-V enlightenments (e.g. +Windows or Hyper-V guests). + +CPUID feature leaves returned by this ioctl are defined by Hyper-V Top Level +Functional Specification (TLFS). These leaves can't be obtained with +KVM_GET_SUPPORTED_CPUID ioctl because some of them intersect with KVM feature +leaves (0x40000000, 0x40000001). + +Currently, the following list of CPUID leaves are returned: + HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS + HYPERV_CPUID_INTERFACE + HYPERV_CPUID_VERSION + HYPERV_CPUID_FEATURES + HYPERV_CPUID_ENLIGHTMENT_INFO + HYPERV_CPUID_IMPLEMENT_LIMITS + HYPERV_CPUID_NESTED_FEATURES + +HYPERV_CPUID_NESTED_FEATURES leaf is only exposed when Enlightened VMCS was +enabled on the corresponding vCPU (KVM_CAP_HYPERV_ENLIGHTENED_VMCS). + +Userspace invokes KVM_GET_SUPPORTED_CPUID by passing a kvm_cpuid2 structure +with the 'nent' field indicating the number of entries in the variable-size +array 'entries'. If the number of entries is too low to describe all Hyper-V +feature leaves, an error (E2BIG) is returned. If the number is more or equal +to the number of Hyper-V feature leaves, the 'nent' field is adjusted to the +number of valid entries in the 'entries' array, which is then filled. + +'index' and 'flags' fields in 'struct kvm_cpuid_entry2' are currently reserved, +userspace should not expect to get any particular value there. + +4.119 KVM_ARM_VCPU_FINALIZE + +Architectures: arm, arm64 +Type: vcpu ioctl +Parameters: int feature (in) +Returns: 0 on success, -1 on error +Errors: + EPERM: feature not enabled, needs configuration, or already finalized + EINVAL: feature unknown or not present + +Recognised values for feature: + arm64 KVM_ARM_VCPU_SVE (requires KVM_CAP_ARM_SVE) + +Finalizes the configuration of the specified vcpu feature. + +The vcpu must already have been initialised, enabling the affected feature, by +means of a successful KVM_ARM_VCPU_INIT call with the appropriate flag set in +features[]. + +For affected vcpu features, this is a mandatory step that must be performed +before the vcpu is fully usable. + +Between KVM_ARM_VCPU_INIT and KVM_ARM_VCPU_FINALIZE, the feature may be +configured by use of ioctls such as KVM_SET_ONE_REG. The exact configuration +that should be performaned and how to do it are feature-dependent. + +Other calls that depend on a particular feature being finalized, such as +KVM_RUN, KVM_GET_REG_LIST, KVM_GET_ONE_REG and KVM_SET_ONE_REG, will fail with +-EPERM unless the feature has already been finalized by means of a +KVM_ARM_VCPU_FINALIZE call. + +See KVM_ARM_VCPU_INIT for details of vcpu features that require finalization +using this ioctl. + +4.120 KVM_SET_PMU_EVENT_FILTER + +Capability: KVM_CAP_PMU_EVENT_FILTER +Architectures: x86 +Type: vm ioctl +Parameters: struct kvm_pmu_event_filter (in) +Returns: 0 on success, -1 on error + +struct kvm_pmu_event_filter { + __u32 action; + __u32 nevents; + __u32 fixed_counter_bitmap; + __u32 flags; + __u32 pad[4]; + __u64 events[0]; +}; + +This ioctl restricts the set of PMU events that the guest can program. +The argument holds a list of events which will be allowed or denied. +The eventsel+umask of each event the guest attempts to program is compared +against the events field to determine whether the guest should have access. +The events field only controls general purpose counters; fixed purpose +counters are controlled by the fixed_counter_bitmap. + +No flags are defined yet, the field must be zero. + +Valid values for 'action': +#define KVM_PMU_EVENT_ALLOW 0 +#define KVM_PMU_EVENT_DENY 1 + + +5. The kvm_run structure +------------------------ + +Application code obtains a pointer to the kvm_run structure by +mmap()ing a vcpu fd. From that point, application code can control +execution by changing fields in kvm_run prior to calling the KVM_RUN +ioctl, and obtain information about the reason KVM_RUN returned by +looking up structure members. + +struct kvm_run { + /* in */ + __u8 request_interrupt_window; + +Request that KVM_RUN return when it becomes possible to inject external +interrupts into the guest. Useful in conjunction with KVM_INTERRUPT. + + __u8 immediate_exit; + +This field is polled once when KVM_RUN starts; if non-zero, KVM_RUN +exits immediately, returning -EINTR. In the common scenario where a +signal is used to "kick" a VCPU out of KVM_RUN, this field can be used +to avoid usage of KVM_SET_SIGNAL_MASK, which has worse scalability. +Rather than blocking the signal outside KVM_RUN, userspace can set up +a signal handler that sets run->immediate_exit to a non-zero value. + +This field is ignored if KVM_CAP_IMMEDIATE_EXIT is not available. + + __u8 padding1[6]; + + /* out */ + __u32 exit_reason; + +When KVM_RUN has returned successfully (return value 0), this informs +application code why KVM_RUN has returned. Allowable values for this +field are detailed below. + + __u8 ready_for_interrupt_injection; + +If request_interrupt_window has been specified, this field indicates +an interrupt can be injected now with KVM_INTERRUPT. + + __u8 if_flag; + +The value of the current interrupt flag. Only valid if in-kernel +local APIC is not used. + + __u16 flags; + +More architecture-specific flags detailing state of the VCPU that may +affect the device's behavior. The only currently defined flag is +KVM_RUN_X86_SMM, which is valid on x86 machines and is set if the +VCPU is in system management mode. + + /* in (pre_kvm_run), out (post_kvm_run) */ + __u64 cr8; + +The value of the cr8 register. Only valid if in-kernel local APIC is +not used. Both input and output. + + __u64 apic_base; + +The value of the APIC BASE msr. Only valid if in-kernel local +APIC is not used. Both input and output. + + union { + /* KVM_EXIT_UNKNOWN */ + struct { + __u64 hardware_exit_reason; + } hw; + +If exit_reason is KVM_EXIT_UNKNOWN, the vcpu has exited due to unknown +reasons. Further architecture-specific information is available in +hardware_exit_reason. + + /* KVM_EXIT_FAIL_ENTRY */ + struct { + __u64 hardware_entry_failure_reason; + } fail_entry; + +If exit_reason is KVM_EXIT_FAIL_ENTRY, the vcpu could not be run due +to unknown reasons. Further architecture-specific information is +available in hardware_entry_failure_reason. + + /* KVM_EXIT_EXCEPTION */ + struct { + __u32 exception; + __u32 error_code; + } ex; + +Unused. + + /* KVM_EXIT_IO */ + struct { +#define KVM_EXIT_IO_IN 0 +#define KVM_EXIT_IO_OUT 1 + __u8 direction; + __u8 size; /* bytes */ + __u16 port; + __u32 count; + __u64 data_offset; /* relative to kvm_run start */ + } io; + +If exit_reason is KVM_EXIT_IO, then the vcpu has +executed a port I/O instruction which could not be satisfied by kvm. +data_offset describes where the data is located (KVM_EXIT_IO_OUT) or +where kvm expects application code to place the data for the next +KVM_RUN invocation (KVM_EXIT_IO_IN). Data format is a packed array. + + /* KVM_EXIT_DEBUG */ + struct { + struct kvm_debug_exit_arch arch; + } debug; + +If the exit_reason is KVM_EXIT_DEBUG, then a vcpu is processing a debug event +for which architecture specific information is returned. + + /* KVM_EXIT_MMIO */ + struct { + __u64 phys_addr; + __u8 data[8]; + __u32 len; + __u8 is_write; + } mmio; + +If exit_reason is KVM_EXIT_MMIO, then the vcpu has +executed a memory-mapped I/O instruction which could not be satisfied +by kvm. The 'data' member contains the written data if 'is_write' is +true, and should be filled by application code otherwise. + +The 'data' member contains, in its first 'len' bytes, the value as it would +appear if the VCPU performed a load or store of the appropriate width directly +to the byte array. + +NOTE: For KVM_EXIT_IO, KVM_EXIT_MMIO, KVM_EXIT_OSI, KVM_EXIT_PAPR and + KVM_EXIT_EPR the corresponding +operations are complete (and guest state is consistent) only after userspace +has re-entered the kernel with KVM_RUN. The kernel side will first finish +incomplete operations and then check for pending signals. Userspace +can re-enter the guest with an unmasked signal pending to complete +pending operations. + + /* KVM_EXIT_HYPERCALL */ + struct { + __u64 nr; + __u64 args[6]; + __u64 ret; + __u32 longmode; + __u32 pad; + } hypercall; + +Unused. This was once used for 'hypercall to userspace'. To implement +such functionality, use KVM_EXIT_IO (x86) or KVM_EXIT_MMIO (all except s390). +Note KVM_EXIT_IO is significantly faster than KVM_EXIT_MMIO. + + /* KVM_EXIT_TPR_ACCESS */ + struct { + __u64 rip; + __u32 is_write; + __u32 pad; + } tpr_access; + +To be documented (KVM_TPR_ACCESS_REPORTING). + + /* KVM_EXIT_S390_SIEIC */ + struct { + __u8 icptcode; + __u64 mask; /* psw upper half */ + __u64 addr; /* psw lower half */ + __u16 ipa; + __u32 ipb; + } s390_sieic; + +s390 specific. + + /* KVM_EXIT_S390_RESET */ +#define KVM_S390_RESET_POR 1 +#define KVM_S390_RESET_CLEAR 2 +#define KVM_S390_RESET_SUBSYSTEM 4 +#define KVM_S390_RESET_CPU_INIT 8 +#define KVM_S390_RESET_IPL 16 + __u64 s390_reset_flags; + +s390 specific. + + /* KVM_EXIT_S390_UCONTROL */ + struct { + __u64 trans_exc_code; + __u32 pgm_code; + } s390_ucontrol; + +s390 specific. A page fault has occurred for a user controlled virtual +machine (KVM_VM_S390_UNCONTROL) on it's host page table that cannot be +resolved by the kernel. +The program code and the translation exception code that were placed +in the cpu's lowcore are presented here as defined by the z Architecture +Principles of Operation Book in the Chapter for Dynamic Address Translation +(DAT) + + /* KVM_EXIT_DCR */ + struct { + __u32 dcrn; + __u32 data; + __u8 is_write; + } dcr; + +Deprecated - was used for 440 KVM. + + /* KVM_EXIT_OSI */ + struct { + __u64 gprs[32]; + } osi; + +MOL uses a special hypercall interface it calls 'OSI'. To enable it, we catch +hypercalls and exit with this exit struct that contains all the guest gprs. + +If exit_reason is KVM_EXIT_OSI, then the vcpu has triggered such a hypercall. +Userspace can now handle the hypercall and when it's done modify the gprs as +necessary. Upon guest entry all guest GPRs will then be replaced by the values +in this struct. + + /* KVM_EXIT_PAPR_HCALL */ + struct { + __u64 nr; + __u64 ret; + __u64 args[9]; + } papr_hcall; + +This is used on 64-bit PowerPC when emulating a pSeries partition, +e.g. with the 'pseries' machine type in qemu. It occurs when the +guest does a hypercall using the 'sc 1' instruction. The 'nr' field +contains the hypercall number (from the guest R3), and 'args' contains +the arguments (from the guest R4 - R12). Userspace should put the +return code in 'ret' and any extra returned values in args[]. +The possible hypercalls are defined in the Power Architecture Platform +Requirements (PAPR) document available from www.power.org (free +developer registration required to access it). + + /* KVM_EXIT_S390_TSCH */ + struct { + __u16 subchannel_id; + __u16 subchannel_nr; + __u32 io_int_parm; + __u32 io_int_word; + __u32 ipb; + __u8 dequeued; + } s390_tsch; + +s390 specific. This exit occurs when KVM_CAP_S390_CSS_SUPPORT has been enabled +and TEST SUBCHANNEL was intercepted. If dequeued is set, a pending I/O +interrupt for the target subchannel has been dequeued and subchannel_id, +subchannel_nr, io_int_parm and io_int_word contain the parameters for that +interrupt. ipb is needed for instruction parameter decoding. + + /* KVM_EXIT_EPR */ + struct { + __u32 epr; + } epr; + +On FSL BookE PowerPC chips, the interrupt controller has a fast patch +interrupt acknowledge path to the core. When the core successfully +delivers an interrupt, it automatically populates the EPR register with +the interrupt vector number and acknowledges the interrupt inside +the interrupt controller. + +In case the interrupt controller lives in user space, we need to do +the interrupt acknowledge cycle through it to fetch the next to be +delivered interrupt vector using this exit. + +It gets triggered whenever both KVM_CAP_PPC_EPR are enabled and an +external interrupt has just been delivered into the guest. User space +should put the acknowledged interrupt vector into the 'epr' field. + + /* KVM_EXIT_SYSTEM_EVENT */ + struct { +#define KVM_SYSTEM_EVENT_SHUTDOWN 1 +#define KVM_SYSTEM_EVENT_RESET 2 +#define KVM_SYSTEM_EVENT_CRASH 3 + __u32 type; + __u64 flags; + } system_event; + +If exit_reason is KVM_EXIT_SYSTEM_EVENT then the vcpu has triggered +a system-level event using some architecture specific mechanism (hypercall +or some special instruction). In case of ARM/ARM64, this is triggered using +HVC instruction based PSCI call from the vcpu. The 'type' field describes +the system-level event type. The 'flags' field describes architecture +specific flags for the system-level event. + +Valid values for 'type' are: + KVM_SYSTEM_EVENT_SHUTDOWN -- the guest has requested a shutdown of the + VM. Userspace is not obliged to honour this, and if it does honour + this does not need to destroy the VM synchronously (ie it may call + KVM_RUN again before shutdown finally occurs). + KVM_SYSTEM_EVENT_RESET -- the guest has requested a reset of the VM. + As with SHUTDOWN, userspace can choose to ignore the request, or + to schedule the reset to occur in the future and may call KVM_RUN again. + KVM_SYSTEM_EVENT_CRASH -- the guest crash occurred and the guest + has requested a crash condition maintenance. Userspace can choose + to ignore the request, or to gather VM memory core dump and/or + reset/shutdown of the VM. + + /* KVM_EXIT_IOAPIC_EOI */ + struct { + __u8 vector; + } eoi; + +Indicates that the VCPU's in-kernel local APIC received an EOI for a +level-triggered IOAPIC interrupt. This exit only triggers when the +IOAPIC is implemented in userspace (i.e. KVM_CAP_SPLIT_IRQCHIP is enabled); +the userspace IOAPIC should process the EOI and retrigger the interrupt if +it is still asserted. Vector is the LAPIC interrupt vector for which the +EOI was received. + + struct kvm_hyperv_exit { +#define KVM_EXIT_HYPERV_SYNIC 1 +#define KVM_EXIT_HYPERV_HCALL 2 + __u32 type; + union { + struct { + __u32 msr; + __u64 control; + __u64 evt_page; + __u64 msg_page; + } synic; + struct { + __u64 input; + __u64 result; + __u64 params[2]; + } hcall; + } u; + }; + /* KVM_EXIT_HYPERV */ + struct kvm_hyperv_exit hyperv; +Indicates that the VCPU exits into userspace to process some tasks +related to Hyper-V emulation. +Valid values for 'type' are: + KVM_EXIT_HYPERV_SYNIC -- synchronously notify user-space about +Hyper-V SynIC state change. Notification is used to remap SynIC +event/message pages and to enable/disable SynIC messages/events processing +in userspace. + + /* Fix the size of the union. */ + char padding[256]; + }; + + /* + * shared registers between kvm and userspace. + * kvm_valid_regs specifies the register classes set by the host + * kvm_dirty_regs specified the register classes dirtied by userspace + * struct kvm_sync_regs is architecture specific, as well as the + * bits for kvm_valid_regs and kvm_dirty_regs + */ + __u64 kvm_valid_regs; + __u64 kvm_dirty_regs; + union { + struct kvm_sync_regs regs; + char padding[SYNC_REGS_SIZE_BYTES]; + } s; + +If KVM_CAP_SYNC_REGS is defined, these fields allow userspace to access +certain guest registers without having to call SET/GET_*REGS. Thus we can +avoid some system call overhead if userspace has to handle the exit. +Userspace can query the validity of the structure by checking +kvm_valid_regs for specific bits. These bits are architecture specific +and usually define the validity of a groups of registers. (e.g. one bit + for general purpose registers) + +Please note that the kernel is allowed to use the kvm_run structure as the +primary storage for certain register types. Therefore, the kernel may use the +values in kvm_run even if the corresponding bit in kvm_dirty_regs is not set. + +}; + + + +6. Capabilities that can be enabled on vCPUs +-------------------------------------------- + +There are certain capabilities that change the behavior of the virtual CPU or +the virtual machine when enabled. To enable them, please see section 4.37. +Below you can find a list of capabilities and what their effect on the vCPU or +the virtual machine is when enabling them. + +The following information is provided along with the description: + + Architectures: which instruction set architectures provide this ioctl. + x86 includes both i386 and x86_64. + + Target: whether this is a per-vcpu or per-vm capability. + + Parameters: what parameters are accepted by the capability. + + Returns: the return value. General error numbers (EBADF, ENOMEM, EINVAL) + are not detailed, but errors with specific meanings are. + + +6.1 KVM_CAP_PPC_OSI + +Architectures: ppc +Target: vcpu +Parameters: none +Returns: 0 on success; -1 on error + +This capability enables interception of OSI hypercalls that otherwise would +be treated as normal system calls to be injected into the guest. OSI hypercalls +were invented by Mac-on-Linux to have a standardized communication mechanism +between the guest and the host. + +When this capability is enabled, KVM_EXIT_OSI can occur. + + +6.2 KVM_CAP_PPC_PAPR + +Architectures: ppc +Target: vcpu +Parameters: none +Returns: 0 on success; -1 on error + +This capability enables interception of PAPR hypercalls. PAPR hypercalls are +done using the hypercall instruction "sc 1". + +It also sets the guest privilege level to "supervisor" mode. Usually the guest +runs in "hypervisor" privilege mode with a few missing features. + +In addition to the above, it changes the semantics of SDR1. In this mode, the +HTAB address part of SDR1 contains an HVA instead of a GPA, as PAPR keeps the +HTAB invisible to the guest. + +When this capability is enabled, KVM_EXIT_PAPR_HCALL can occur. + + +6.3 KVM_CAP_SW_TLB + +Architectures: ppc +Target: vcpu +Parameters: args[0] is the address of a struct kvm_config_tlb +Returns: 0 on success; -1 on error + +struct kvm_config_tlb { + __u64 params; + __u64 array; + __u32 mmu_type; + __u32 array_len; +}; + +Configures the virtual CPU's TLB array, establishing a shared memory area +between userspace and KVM. The "params" and "array" fields are userspace +addresses of mmu-type-specific data structures. The "array_len" field is an +safety mechanism, and should be set to the size in bytes of the memory that +userspace has reserved for the array. It must be at least the size dictated +by "mmu_type" and "params". + +While KVM_RUN is active, the shared region is under control of KVM. Its +contents are undefined, and any modification by userspace results in +boundedly undefined behavior. + +On return from KVM_RUN, the shared region will reflect the current state of +the guest's TLB. If userspace makes any changes, it must call KVM_DIRTY_TLB +to tell KVM which entries have been changed, prior to calling KVM_RUN again +on this vcpu. + +For mmu types KVM_MMU_FSL_BOOKE_NOHV and KVM_MMU_FSL_BOOKE_HV: + - The "params" field is of type "struct kvm_book3e_206_tlb_params". + - The "array" field points to an array of type "struct + kvm_book3e_206_tlb_entry". + - The array consists of all entries in the first TLB, followed by all + entries in the second TLB. + - Within a TLB, entries are ordered first by increasing set number. Within a + set, entries are ordered by way (increasing ESEL). + - The hash for determining set number in TLB0 is: (MAS2 >> 12) & (num_sets - 1) + where "num_sets" is the tlb_sizes[] value divided by the tlb_ways[] value. + - The tsize field of mas1 shall be set to 4K on TLB0, even though the + hardware ignores this value for TLB0. + +6.4 KVM_CAP_S390_CSS_SUPPORT + +Architectures: s390 +Target: vcpu +Parameters: none +Returns: 0 on success; -1 on error + +This capability enables support for handling of channel I/O instructions. + +TEST PENDING INTERRUPTION and the interrupt portion of TEST SUBCHANNEL are +handled in-kernel, while the other I/O instructions are passed to userspace. + +When this capability is enabled, KVM_EXIT_S390_TSCH will occur on TEST +SUBCHANNEL intercepts. + +Note that even though this capability is enabled per-vcpu, the complete +virtual machine is affected. + +6.5 KVM_CAP_PPC_EPR + +Architectures: ppc +Target: vcpu +Parameters: args[0] defines whether the proxy facility is active +Returns: 0 on success; -1 on error + +This capability enables or disables the delivery of interrupts through the +external proxy facility. + +When enabled (args[0] != 0), every time the guest gets an external interrupt +delivered, it automatically exits into user space with a KVM_EXIT_EPR exit +to receive the topmost interrupt vector. + +When disabled (args[0] == 0), behavior is as if this facility is unsupported. + +When this capability is enabled, KVM_EXIT_EPR can occur. + +6.6 KVM_CAP_IRQ_MPIC + +Architectures: ppc +Parameters: args[0] is the MPIC device fd + args[1] is the MPIC CPU number for this vcpu + +This capability connects the vcpu to an in-kernel MPIC device. + +6.7 KVM_CAP_IRQ_XICS + +Architectures: ppc +Target: vcpu +Parameters: args[0] is the XICS device fd + args[1] is the XICS CPU number (server ID) for this vcpu + +This capability connects the vcpu to an in-kernel XICS device. + +6.8 KVM_CAP_S390_IRQCHIP + +Architectures: s390 +Target: vm +Parameters: none + +This capability enables the in-kernel irqchip for s390. Please refer to +"4.24 KVM_CREATE_IRQCHIP" for details. + +6.9 KVM_CAP_MIPS_FPU + +Architectures: mips +Target: vcpu +Parameters: args[0] is reserved for future use (should be 0). + +This capability allows the use of the host Floating Point Unit by the guest. It +allows the Config1.FP bit to be set to enable the FPU in the guest. Once this is +done the KVM_REG_MIPS_FPR_* and KVM_REG_MIPS_FCR_* registers can be accessed +(depending on the current guest FPU register mode), and the Status.FR, +Config5.FRE bits are accessible via the KVM API and also from the guest, +depending on them being supported by the FPU. + +6.10 KVM_CAP_MIPS_MSA + +Architectures: mips +Target: vcpu +Parameters: args[0] is reserved for future use (should be 0). + +This capability allows the use of the MIPS SIMD Architecture (MSA) by the guest. +It allows the Config3.MSAP bit to be set to enable the use of MSA by the guest. +Once this is done the KVM_REG_MIPS_VEC_* and KVM_REG_MIPS_MSA_* registers can be +accessed, and the Config5.MSAEn bit is accessible via the KVM API and also from +the guest. + +6.74 KVM_CAP_SYNC_REGS +Architectures: s390, x86 +Target: s390: always enabled, x86: vcpu +Parameters: none +Returns: x86: KVM_CHECK_EXTENSION returns a bit-array indicating which register +sets are supported (bitfields defined in arch/x86/include/uapi/asm/kvm.h). + +As described above in the kvm_sync_regs struct info in section 5 (kvm_run): +KVM_CAP_SYNC_REGS "allow[s] userspace to access certain guest registers +without having to call SET/GET_*REGS". This reduces overhead by eliminating +repeated ioctl calls for setting and/or getting register values. This is +particularly important when userspace is making synchronous guest state +modifications, e.g. when emulating and/or intercepting instructions in +userspace. + +For s390 specifics, please refer to the source code. + +For x86: +- the register sets to be copied out to kvm_run are selectable + by userspace (rather that all sets being copied out for every exit). +- vcpu_events are available in addition to regs and sregs. + +For x86, the 'kvm_valid_regs' field of struct kvm_run is overloaded to +function as an input bit-array field set by userspace to indicate the +specific register sets to be copied out on the next exit. + +To indicate when userspace has modified values that should be copied into +the vCPU, the all architecture bitarray field, 'kvm_dirty_regs' must be set. +This is done using the same bitflags as for the 'kvm_valid_regs' field. +If the dirty bit is not set, then the register set values will not be copied +into the vCPU even if they've been modified. + +Unused bitfields in the bitarrays must be set to zero. + +struct kvm_sync_regs { + struct kvm_regs regs; + struct kvm_sregs sregs; + struct kvm_vcpu_events events; +}; + +6.75 KVM_CAP_PPC_IRQ_XIVE + +Architectures: ppc +Target: vcpu +Parameters: args[0] is the XIVE device fd + args[1] is the XIVE CPU number (server ID) for this vcpu + +This capability connects the vcpu to an in-kernel XIVE device. + +7. Capabilities that can be enabled on VMs +------------------------------------------ + +There are certain capabilities that change the behavior of the virtual +machine when enabled. To enable them, please see section 4.37. Below +you can find a list of capabilities and what their effect on the VM +is when enabling them. + +The following information is provided along with the description: + + Architectures: which instruction set architectures provide this ioctl. + x86 includes both i386 and x86_64. + + Parameters: what parameters are accepted by the capability. + + Returns: the return value. General error numbers (EBADF, ENOMEM, EINVAL) + are not detailed, but errors with specific meanings are. + + +7.1 KVM_CAP_PPC_ENABLE_HCALL + +Architectures: ppc +Parameters: args[0] is the sPAPR hcall number + args[1] is 0 to disable, 1 to enable in-kernel handling + +This capability controls whether individual sPAPR hypercalls (hcalls) +get handled by the kernel or not. Enabling or disabling in-kernel +handling of an hcall is effective across the VM. On creation, an +initial set of hcalls are enabled for in-kernel handling, which +consists of those hcalls for which in-kernel handlers were implemented +before this capability was implemented. If disabled, the kernel will +not to attempt to handle the hcall, but will always exit to userspace +to handle it. Note that it may not make sense to enable some and +disable others of a group of related hcalls, but KVM does not prevent +userspace from doing that. + +If the hcall number specified is not one that has an in-kernel +implementation, the KVM_ENABLE_CAP ioctl will fail with an EINVAL +error. + +7.2 KVM_CAP_S390_USER_SIGP + +Architectures: s390 +Parameters: none + +This capability controls which SIGP orders will be handled completely in user +space. With this capability enabled, all fast orders will be handled completely +in the kernel: +- SENSE +- SENSE RUNNING +- EXTERNAL CALL +- EMERGENCY SIGNAL +- CONDITIONAL EMERGENCY SIGNAL + +All other orders will be handled completely in user space. + +Only privileged operation exceptions will be checked for in the kernel (or even +in the hardware prior to interception). If this capability is not enabled, the +old way of handling SIGP orders is used (partially in kernel and user space). + +7.3 KVM_CAP_S390_VECTOR_REGISTERS + +Architectures: s390 +Parameters: none +Returns: 0 on success, negative value on error + +Allows use of the vector registers introduced with z13 processor, and +provides for the synchronization between host and user space. Will +return -EINVAL if the machine does not support vectors. + +7.4 KVM_CAP_S390_USER_STSI + +Architectures: s390 +Parameters: none + +This capability allows post-handlers for the STSI instruction. After +initial handling in the kernel, KVM exits to user space with +KVM_EXIT_S390_STSI to allow user space to insert further data. + +Before exiting to userspace, kvm handlers should fill in s390_stsi field of +vcpu->run: +struct { + __u64 addr; + __u8 ar; + __u8 reserved; + __u8 fc; + __u8 sel1; + __u16 sel2; +} s390_stsi; + +@addr - guest address of STSI SYSIB +@fc - function code +@sel1 - selector 1 +@sel2 - selector 2 +@ar - access register number + +KVM handlers should exit to userspace with rc = -EREMOTE. + +7.5 KVM_CAP_SPLIT_IRQCHIP + +Architectures: x86 +Parameters: args[0] - number of routes reserved for userspace IOAPICs +Returns: 0 on success, -1 on error + +Create a local apic for each processor in the kernel. This can be used +instead of KVM_CREATE_IRQCHIP if the userspace VMM wishes to emulate the +IOAPIC and PIC (and also the PIT, even though this has to be enabled +separately). + +This capability also enables in kernel routing of interrupt requests; +when KVM_CAP_SPLIT_IRQCHIP only routes of KVM_IRQ_ROUTING_MSI type are +used in the IRQ routing table. The first args[0] MSI routes are reserved +for the IOAPIC pins. Whenever the LAPIC receives an EOI for these routes, +a KVM_EXIT_IOAPIC_EOI vmexit will be reported to userspace. + +Fails if VCPU has already been created, or if the irqchip is already in the +kernel (i.e. KVM_CREATE_IRQCHIP has already been called). + +7.6 KVM_CAP_S390_RI + +Architectures: s390 +Parameters: none + +Allows use of runtime-instrumentation introduced with zEC12 processor. +Will return -EINVAL if the machine does not support runtime-instrumentation. +Will return -EBUSY if a VCPU has already been created. + +7.7 KVM_CAP_X2APIC_API + +Architectures: x86 +Parameters: args[0] - features that should be enabled +Returns: 0 on success, -EINVAL when args[0] contains invalid features + +Valid feature flags in args[0] are + +#define KVM_X2APIC_API_USE_32BIT_IDS (1ULL << 0) +#define KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK (1ULL << 1) + +Enabling KVM_X2APIC_API_USE_32BIT_IDS changes the behavior of +KVM_SET_GSI_ROUTING, KVM_SIGNAL_MSI, KVM_SET_LAPIC, and KVM_GET_LAPIC, +allowing the use of 32-bit APIC IDs. See KVM_CAP_X2APIC_API in their +respective sections. + +KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK must be enabled for x2APIC to work +in logical mode or with more than 255 VCPUs. Otherwise, KVM treats 0xff +as a broadcast even in x2APIC mode in order to support physical x2APIC +without interrupt remapping. This is undesirable in logical mode, +where 0xff represents CPUs 0-7 in cluster 0. + +7.8 KVM_CAP_S390_USER_INSTR0 + +Architectures: s390 +Parameters: none + +With this capability enabled, all illegal instructions 0x0000 (2 bytes) will +be intercepted and forwarded to user space. User space can use this +mechanism e.g. to realize 2-byte software breakpoints. The kernel will +not inject an operating exception for these instructions, user space has +to take care of that. + +This capability can be enabled dynamically even if VCPUs were already +created and are running. + +7.9 KVM_CAP_S390_GS + +Architectures: s390 +Parameters: none +Returns: 0 on success; -EINVAL if the machine does not support + guarded storage; -EBUSY if a VCPU has already been created. + +Allows use of guarded storage for the KVM guest. + +7.10 KVM_CAP_S390_AIS + +Architectures: s390 +Parameters: none + +Allow use of adapter-interruption suppression. +Returns: 0 on success; -EBUSY if a VCPU has already been created. + +7.11 KVM_CAP_PPC_SMT + +Architectures: ppc +Parameters: vsmt_mode, flags + +Enabling this capability on a VM provides userspace with a way to set +the desired virtual SMT mode (i.e. the number of virtual CPUs per +virtual core). The virtual SMT mode, vsmt_mode, must be a power of 2 +between 1 and 8. On POWER8, vsmt_mode must also be no greater than +the number of threads per subcore for the host. Currently flags must +be 0. A successful call to enable this capability will result in +vsmt_mode being returned when the KVM_CAP_PPC_SMT capability is +subsequently queried for the VM. This capability is only supported by +HV KVM, and can only be set before any VCPUs have been created. +The KVM_CAP_PPC_SMT_POSSIBLE capability indicates which virtual SMT +modes are available. + +7.12 KVM_CAP_PPC_FWNMI + +Architectures: ppc +Parameters: none + +With this capability a machine check exception in the guest address +space will cause KVM to exit the guest with NMI exit reason. This +enables QEMU to build error log and branch to guest kernel registered +machine check handling routine. Without this capability KVM will +branch to guests' 0x200 interrupt vector. + +7.13 KVM_CAP_X86_DISABLE_EXITS + +Architectures: x86 +Parameters: args[0] defines which exits are disabled +Returns: 0 on success, -EINVAL when args[0] contains invalid exits + +Valid bits in args[0] are + +#define KVM_X86_DISABLE_EXITS_MWAIT (1 << 0) +#define KVM_X86_DISABLE_EXITS_HLT (1 << 1) +#define KVM_X86_DISABLE_EXITS_PAUSE (1 << 2) +#define KVM_X86_DISABLE_EXITS_CSTATE (1 << 3) + +Enabling this capability on a VM provides userspace with a way to no +longer intercept some instructions for improved latency in some +workloads, and is suggested when vCPUs are associated to dedicated +physical CPUs. More bits can be added in the future; userspace can +just pass the KVM_CHECK_EXTENSION result to KVM_ENABLE_CAP to disable +all such vmexits. + +Do not enable KVM_FEATURE_PV_UNHALT if you disable HLT exits. + +7.14 KVM_CAP_S390_HPAGE_1M + +Architectures: s390 +Parameters: none +Returns: 0 on success, -EINVAL if hpage module parameter was not set + or cmma is enabled, or the VM has the KVM_VM_S390_UCONTROL + flag set + +With this capability the KVM support for memory backing with 1m pages +through hugetlbfs can be enabled for a VM. After the capability is +enabled, cmma can't be enabled anymore and pfmfi and the storage key +interpretation are disabled. If cmma has already been enabled or the +hpage module parameter is not set to 1, -EINVAL is returned. + +While it is generally possible to create a huge page backed VM without +this capability, the VM will not be able to run. + +7.15 KVM_CAP_MSR_PLATFORM_INFO + +Architectures: x86 +Parameters: args[0] whether feature should be enabled or not + +With this capability, a guest may read the MSR_PLATFORM_INFO MSR. Otherwise, +a #GP would be raised when the guest tries to access. Currently, this +capability does not enable write permissions of this MSR for the guest. + +7.16 KVM_CAP_PPC_NESTED_HV + +Architectures: ppc +Parameters: none +Returns: 0 on success, -EINVAL when the implementation doesn't support + nested-HV virtualization. + +HV-KVM on POWER9 and later systems allows for "nested-HV" +virtualization, which provides a way for a guest VM to run guests that +can run using the CPU's supervisor mode (privileged non-hypervisor +state). Enabling this capability on a VM depends on the CPU having +the necessary functionality and on the facility being enabled with a +kvm-hv module parameter. + +7.17 KVM_CAP_EXCEPTION_PAYLOAD + +Architectures: x86 +Parameters: args[0] whether feature should be enabled or not + +With this capability enabled, CR2 will not be modified prior to the +emulated VM-exit when L1 intercepts a #PF exception that occurs in +L2. Similarly, for kvm-intel only, DR6 will not be modified prior to +the emulated VM-exit when L1 intercepts a #DB exception that occurs in +L2. As a result, when KVM_GET_VCPU_EVENTS reports a pending #PF (or +#DB) exception for L2, exception.has_payload will be set and the +faulting address (or the new DR6 bits*) will be reported in the +exception_payload field. Similarly, when userspace injects a #PF (or +#DB) into L2 using KVM_SET_VCPU_EVENTS, it is expected to set +exception.has_payload and to put the faulting address (or the new DR6 +bits*) in the exception_payload field. + +This capability also enables exception.pending in struct +kvm_vcpu_events, which allows userspace to distinguish between pending +and injected exceptions. + + +* For the new DR6 bits, note that bit 16 is set iff the #DB exception + will clear DR6.RTM. + +7.18 KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 + +Architectures: x86, arm, arm64, mips +Parameters: args[0] whether feature should be enabled or not + +With this capability enabled, KVM_GET_DIRTY_LOG will not automatically +clear and write-protect all pages that are returned as dirty. +Rather, userspace will have to do this operation separately using +KVM_CLEAR_DIRTY_LOG. + +At the cost of a slightly more complicated operation, this provides better +scalability and responsiveness for two reasons. First, +KVM_CLEAR_DIRTY_LOG ioctl can operate on a 64-page granularity rather +than requiring to sync a full memslot; this ensures that KVM does not +take spinlocks for an extended period of time. Second, in some cases a +large amount of time can pass between a call to KVM_GET_DIRTY_LOG and +userspace actually using the data in the page. Pages can be modified +during this time, which is inefficint for both the guest and userspace: +the guest will incur a higher penalty due to write protection faults, +while userspace can see false reports of dirty pages. Manual reprotection +helps reducing this time, improving guest performance and reducing the +number of dirty log false positives. + +KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 was previously available under the name +KVM_CAP_MANUAL_DIRTY_LOG_PROTECT, but the implementation had bugs that make +it hard or impossible to use it correctly. The availability of +KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2 signals that those bugs are fixed. +Userspace should not try to use KVM_CAP_MANUAL_DIRTY_LOG_PROTECT. + +8. Other capabilities. +---------------------- + +This section lists capabilities that give information about other +features of the KVM implementation. + +8.1 KVM_CAP_PPC_HWRNG + +Architectures: ppc + +This capability, if KVM_CHECK_EXTENSION indicates that it is +available, means that that the kernel has an implementation of the +H_RANDOM hypercall backed by a hardware random-number generator. +If present, the kernel H_RANDOM handler can be enabled for guest use +with the KVM_CAP_PPC_ENABLE_HCALL capability. + +8.2 KVM_CAP_HYPERV_SYNIC + +Architectures: x86 +This capability, if KVM_CHECK_EXTENSION indicates that it is +available, means that that the kernel has an implementation of the +Hyper-V Synthetic interrupt controller(SynIC). Hyper-V SynIC is +used to support Windows Hyper-V based guest paravirt drivers(VMBus). + +In order to use SynIC, it has to be activated by setting this +capability via KVM_ENABLE_CAP ioctl on the vcpu fd. Note that this +will disable the use of APIC hardware virtualization even if supported +by the CPU, as it's incompatible with SynIC auto-EOI behavior. + +8.3 KVM_CAP_PPC_RADIX_MMU + +Architectures: ppc + +This capability, if KVM_CHECK_EXTENSION indicates that it is +available, means that that the kernel can support guests using the +radix MMU defined in Power ISA V3.00 (as implemented in the POWER9 +processor). + +8.4 KVM_CAP_PPC_HASH_MMU_V3 + +Architectures: ppc + +This capability, if KVM_CHECK_EXTENSION indicates that it is +available, means that that the kernel can support guests using the +hashed page table MMU defined in Power ISA V3.00 (as implemented in +the POWER9 processor), including in-memory segment tables. + +8.5 KVM_CAP_MIPS_VZ + +Architectures: mips + +This capability, if KVM_CHECK_EXTENSION on the main kvm handle indicates that +it is available, means that full hardware assisted virtualization capabilities +of the hardware are available for use through KVM. An appropriate +KVM_VM_MIPS_* type must be passed to KVM_CREATE_VM to create a VM which +utilises it. + +If KVM_CHECK_EXTENSION on a kvm VM handle indicates that this capability is +available, it means that the VM is using full hardware assisted virtualization +capabilities of the hardware. This is useful to check after creating a VM with +KVM_VM_MIPS_DEFAULT. + +The value returned by KVM_CHECK_EXTENSION should be compared against known +values (see below). All other values are reserved. This is to allow for the +possibility of other hardware assisted virtualization implementations which +may be incompatible with the MIPS VZ ASE. + + 0: The trap & emulate implementation is in use to run guest code in user + mode. Guest virtual memory segments are rearranged to fit the guest in the + user mode address space. + + 1: The MIPS VZ ASE is in use, providing full hardware assisted + virtualization, including standard guest virtual memory segments. + +8.6 KVM_CAP_MIPS_TE + +Architectures: mips + +This capability, if KVM_CHECK_EXTENSION on the main kvm handle indicates that +it is available, means that the trap & emulate implementation is available to +run guest code in user mode, even if KVM_CAP_MIPS_VZ indicates that hardware +assisted virtualisation is also available. KVM_VM_MIPS_TE (0) must be passed +to KVM_CREATE_VM to create a VM which utilises it. + +If KVM_CHECK_EXTENSION on a kvm VM handle indicates that this capability is +available, it means that the VM is using trap & emulate. + +8.7 KVM_CAP_MIPS_64BIT + +Architectures: mips + +This capability indicates the supported architecture type of the guest, i.e. the +supported register and address width. + +The values returned when this capability is checked by KVM_CHECK_EXTENSION on a +kvm VM handle correspond roughly to the CP0_Config.AT register field, and should +be checked specifically against known values (see below). All other values are +reserved. + + 0: MIPS32 or microMIPS32. + Both registers and addresses are 32-bits wide. + It will only be possible to run 32-bit guest code. + + 1: MIPS64 or microMIPS64 with access only to 32-bit compatibility segments. + Registers are 64-bits wide, but addresses are 32-bits wide. + 64-bit guest code may run but cannot access MIPS64 memory segments. + It will also be possible to run 32-bit guest code. + + 2: MIPS64 or microMIPS64 with access to all address segments. + Both registers and addresses are 64-bits wide. + It will be possible to run 64-bit or 32-bit guest code. + +8.9 KVM_CAP_ARM_USER_IRQ + +Architectures: arm, arm64 +This capability, if KVM_CHECK_EXTENSION indicates that it is available, means +that if userspace creates a VM without an in-kernel interrupt controller, it +will be notified of changes to the output level of in-kernel emulated devices, +which can generate virtual interrupts, presented to the VM. +For such VMs, on every return to userspace, the kernel +updates the vcpu's run->s.regs.device_irq_level field to represent the actual +output level of the device. + +Whenever kvm detects a change in the device output level, kvm guarantees at +least one return to userspace before running the VM. This exit could either +be a KVM_EXIT_INTR or any other exit event, like KVM_EXIT_MMIO. This way, +userspace can always sample the device output level and re-compute the state of +the userspace interrupt controller. Userspace should always check the state +of run->s.regs.device_irq_level on every kvm exit. +The value in run->s.regs.device_irq_level can represent both level and edge +triggered interrupt signals, depending on the device. Edge triggered interrupt +signals will exit to userspace with the bit in run->s.regs.device_irq_level +set exactly once per edge signal. + +The field run->s.regs.device_irq_level is available independent of +run->kvm_valid_regs or run->kvm_dirty_regs bits. + +If KVM_CAP_ARM_USER_IRQ is supported, the KVM_CHECK_EXTENSION ioctl returns a +number larger than 0 indicating the version of this capability is implemented +and thereby which bits in in run->s.regs.device_irq_level can signal values. + +Currently the following bits are defined for the device_irq_level bitmap: + + KVM_CAP_ARM_USER_IRQ >= 1: + + KVM_ARM_DEV_EL1_VTIMER - EL1 virtual timer + KVM_ARM_DEV_EL1_PTIMER - EL1 physical timer + KVM_ARM_DEV_PMU - ARM PMU overflow interrupt signal + +Future versions of kvm may implement additional events. These will get +indicated by returning a higher number from KVM_CHECK_EXTENSION and will be +listed above. + +8.10 KVM_CAP_PPC_SMT_POSSIBLE + +Architectures: ppc + +Querying this capability returns a bitmap indicating the possible +virtual SMT modes that can be set using KVM_CAP_PPC_SMT. If bit N +(counting from the right) is set, then a virtual SMT mode of 2^N is +available. + +8.11 KVM_CAP_HYPERV_SYNIC2 + +Architectures: x86 + +This capability enables a newer version of Hyper-V Synthetic interrupt +controller (SynIC). The only difference with KVM_CAP_HYPERV_SYNIC is that KVM +doesn't clear SynIC message and event flags pages when they are enabled by +writing to the respective MSRs. + +8.12 KVM_CAP_HYPERV_VP_INDEX + +Architectures: x86 + +This capability indicates that userspace can load HV_X64_MSR_VP_INDEX msr. Its +value is used to denote the target vcpu for a SynIC interrupt. For +compatibilty, KVM initializes this msr to KVM's internal vcpu index. When this +capability is absent, userspace can still query this msr's value. + +8.13 KVM_CAP_S390_AIS_MIGRATION + +Architectures: s390 +Parameters: none + +This capability indicates if the flic device will be able to get/set the +AIS states for migration via the KVM_DEV_FLIC_AISM_ALL attribute and allows +to discover this without having to create a flic device. + +8.14 KVM_CAP_S390_PSW + +Architectures: s390 + +This capability indicates that the PSW is exposed via the kvm_run structure. + +8.15 KVM_CAP_S390_GMAP + +Architectures: s390 + +This capability indicates that the user space memory used as guest mapping can +be anywhere in the user memory address space, as long as the memory slots are +aligned and sized to a segment (1MB) boundary. + +8.16 KVM_CAP_S390_COW + +Architectures: s390 + +This capability indicates that the user space memory used as guest mapping can +use copy-on-write semantics as well as dirty pages tracking via read-only page +tables. + +8.17 KVM_CAP_S390_BPB + +Architectures: s390 + +This capability indicates that kvm will implement the interfaces to handle +reset, migration and nested KVM for branch prediction blocking. The stfle +facility 82 should not be provided to the guest without this capability. + +8.18 KVM_CAP_HYPERV_TLBFLUSH + +Architectures: x86 + +This capability indicates that KVM supports paravirtualized Hyper-V TLB Flush +hypercalls: +HvFlushVirtualAddressSpace, HvFlushVirtualAddressSpaceEx, +HvFlushVirtualAddressList, HvFlushVirtualAddressListEx. + +8.19 KVM_CAP_ARM_INJECT_SERROR_ESR + +Architectures: arm, arm64 + +This capability indicates that userspace can specify (via the +KVM_SET_VCPU_EVENTS ioctl) the syndrome value reported to the guest when it +takes a virtual SError interrupt exception. +If KVM advertises this capability, userspace can only specify the ISS field for +the ESR syndrome. Other parts of the ESR, such as the EC are generated by the +CPU when the exception is taken. If this virtual SError is taken to EL1 using +AArch64, this value will be reported in the ISS field of ESR_ELx. + +See KVM_CAP_VCPU_EVENTS for more details. +8.20 KVM_CAP_HYPERV_SEND_IPI + +Architectures: x86 + +This capability indicates that KVM supports paravirtualized Hyper-V IPI send +hypercalls: +HvCallSendSyntheticClusterIpi, HvCallSendSyntheticClusterIpiEx. diff --git a/Documentation/virt/kvm/arm/hyp-abi.txt b/Documentation/virt/kvm/arm/hyp-abi.txt new file mode 100644 index 000000000000..a20a0bee268d --- /dev/null +++ b/Documentation/virt/kvm/arm/hyp-abi.txt @@ -0,0 +1,53 @@ +* Internal ABI between the kernel and HYP + +This file documents the interaction between the Linux kernel and the +hypervisor layer when running Linux as a hypervisor (for example +KVM). It doesn't cover the interaction of the kernel with the +hypervisor when running as a guest (under Xen, KVM or any other +hypervisor), or any hypervisor-specific interaction when the kernel is +used as a host. + +On arm and arm64 (without VHE), the kernel doesn't run in hypervisor +mode, but still needs to interact with it, allowing a built-in +hypervisor to be either installed or torn down. + +In order to achieve this, the kernel must be booted at HYP (arm) or +EL2 (arm64), allowing it to install a set of stubs before dropping to +SVC/EL1. These stubs are accessible by using a 'hvc #0' instruction, +and only act on individual CPUs. + +Unless specified otherwise, any built-in hypervisor must implement +these functions (see arch/arm{,64}/include/asm/virt.h): + +* r0/x0 = HVC_SET_VECTORS + r1/x1 = vectors + + Set HVBAR/VBAR_EL2 to 'vectors' to enable a hypervisor. 'vectors' + must be a physical address, and respect the alignment requirements + of the architecture. Only implemented by the initial stubs, not by + Linux hypervisors. + +* r0/x0 = HVC_RESET_VECTORS + + Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials + stubs' exception vector value. This effectively disables an existing + hypervisor. + +* r0/x0 = HVC_SOFT_RESTART + r1/x1 = restart address + x2 = x0's value when entering the next payload (arm64) + x3 = x1's value when entering the next payload (arm64) + x4 = x2's value when entering the next payload (arm64) + + Mask all exceptions, disable the MMU, move the arguments into place + (arm64 only), and jump to the restart address while at HYP/EL2. This + hypercall is not expected to return to its caller. + +Any other value of r0/x0 triggers a hypervisor-specific handling, +which is not documented here. + +The return value of a stub hypercall is held by r0/x0, and is 0 on +success, and HVC_STUB_ERR on error. A stub hypercall is allowed to +clobber any of the caller-saved registers (x0-x18 on arm64, r0-r3 and +ip on arm). It is thus recommended to use a function call to perform +the hypercall. diff --git a/Documentation/virt/kvm/arm/psci.txt b/Documentation/virt/kvm/arm/psci.txt new file mode 100644 index 000000000000..559586fc9d37 --- /dev/null +++ b/Documentation/virt/kvm/arm/psci.txt @@ -0,0 +1,61 @@ +KVM implements the PSCI (Power State Coordination Interface) +specification in order to provide services such as CPU on/off, reset +and power-off to the guest. + +The PSCI specification is regularly updated to provide new features, +and KVM implements these updates if they make sense from a virtualization +point of view. + +This means that a guest booted on two different versions of KVM can +observe two different "firmware" revisions. This could cause issues if +a given guest is tied to a particular PSCI revision (unlikely), or if +a migration causes a different PSCI version to be exposed out of the +blue to an unsuspecting guest. + +In order to remedy this situation, KVM exposes a set of "firmware +pseudo-registers" that can be manipulated using the GET/SET_ONE_REG +interface. These registers can be saved/restored by userspace, and set +to a convenient value if required. + +The following register is defined: + +* KVM_REG_ARM_PSCI_VERSION: + + - Only valid if the vcpu has the KVM_ARM_VCPU_PSCI_0_2 feature set + (and thus has already been initialized) + - Returns the current PSCI version on GET_ONE_REG (defaulting to the + highest PSCI version implemented by KVM and compatible with v0.2) + - Allows any PSCI version implemented by KVM and compatible with + v0.2 to be set with SET_ONE_REG + - Affects the whole VM (even if the register view is per-vcpu) + +* KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1: + Holds the state of the firmware support to mitigate CVE-2017-5715, as + offered by KVM to the guest via a HVC call. The workaround is described + under SMCCC_ARCH_WORKAROUND_1 in [1]. + Accepted values are: + KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL: KVM does not offer + firmware support for the workaround. The mitigation status for the + guest is unknown. + KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL: The workaround HVC call is + available to the guest and required for the mitigation. + KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_REQUIRED: The workaround HVC call + is available to the guest, but it is not needed on this VCPU. + +* KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2: + Holds the state of the firmware support to mitigate CVE-2018-3639, as + offered by KVM to the guest via a HVC call. The workaround is described + under SMCCC_ARCH_WORKAROUND_2 in [1]. + Accepted values are: + KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL: A workaround is not + available. KVM does not offer firmware support for the workaround. + KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN: The workaround state is + unknown. KVM does not offer firmware support for the workaround. + KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL: The workaround is available, + and can be disabled by a vCPU. If + KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED is set, it is active for + this vCPU. + KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED: The workaround is + always active on this vCPU or it is not needed. + +[1] https://developer.arm.com/-/media/developer/pdf/ARM_DEN_0070A_Firmware_interfaces_for_mitigating_CVE-2017-5715.pdf diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst new file mode 100644 index 000000000000..01b081f6e7ea --- /dev/null +++ b/Documentation/virt/kvm/cpuid.rst @@ -0,0 +1,107 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============== +KVM CPUID bits +============== + +:Author: Glauber Costa <glommer@gmail.com> + +A guest running on a kvm host, can check some of its features using +cpuid. This is not always guaranteed to work, since userspace can +mask-out some, or even all KVM-related cpuid features before launching +a guest. + +KVM cpuid functions are: + +function: KVM_CPUID_SIGNATURE (0x40000000) + +returns:: + + eax = 0x40000001 + ebx = 0x4b4d564b + ecx = 0x564b4d56 + edx = 0x4d + +Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM". +The value in eax corresponds to the maximum cpuid function present in this leaf, +and will be updated if more functions are added in the future. +Note also that old hosts set eax value to 0x0. This should +be interpreted as if the value was 0x40000001. +This function queries the presence of KVM cpuid leafs. + +function: define KVM_CPUID_FEATURES (0x40000001) + +returns:: + + ebx, ecx + eax = an OR'ed group of (1 << flag) + +where ``flag`` is defined as below: + +================================= =========== ================================ +flag value meaning +================================= =========== ================================ +KVM_FEATURE_CLOCKSOURCE 0 kvmclock available at msrs + 0x11 and 0x12 + +KVM_FEATURE_NOP_IO_DELAY 1 not necessary to perform delays + on PIO operations + +KVM_FEATURE_MMU_OP 2 deprecated + +KVM_FEATURE_CLOCKSOURCE2 3 kvmclock available at msrs + + 0x4b564d00 and 0x4b564d01 +KVM_FEATURE_ASYNC_PF 4 async pf can be enabled by + writing to msr 0x4b564d02 + +KVM_FEATURE_STEAL_TIME 5 steal time can be enabled by + writing to msr 0x4b564d03 + +KVM_FEATURE_PV_EOI 6 paravirtualized end of interrupt + handler can be enabled by + writing to msr 0x4b564d04 + +KVM_FEATURE_PV_UNHAULT 7 guest checks this feature bit + before enabling paravirtualized + spinlock support + +KVM_FEATURE_PV_TLB_FLUSH 9 guest checks this feature bit + before enabling paravirtualized + tlb flush + +KVM_FEATURE_ASYNC_PF_VMEXIT 10 paravirtualized async PF VM EXIT + can be enabled by setting bit 2 + when writing to msr 0x4b564d02 + +KVM_FEATURE_PV_SEND_IPI 11 guest checks this feature bit + before enabling paravirtualized + sebd IPIs + +KVM_FEATURE_PV_POLL_CONTROL 12 host-side polling on HLT can + be disabled by writing + to msr 0x4b564d05. + +KVM_FEATURE_PV_SCHED_YIELD 13 guest checks this feature bit + before using paravirtualized + sched yield. + +KVM_FEATURE_CLOCSOURCE_STABLE_BIT 24 host will warn if no guest-side + per-cpu warps are expeced in + kvmclock +================================= =========== ================================ + +:: + + edx = an OR'ed group of (1 << flag) + +Where ``flag`` here is defined as below: + +================== ============ ================================= +flag value meaning +================== ============ ================================= +KVM_HINTS_REALTIME 0 guest checks this feature bit to + determine that vCPUs are never + preempted for an unlimited time + allowing optimizations +================== ============ ================================= diff --git a/Documentation/virt/kvm/devices/README b/Documentation/virt/kvm/devices/README new file mode 100644 index 000000000000..34a69834124a --- /dev/null +++ b/Documentation/virt/kvm/devices/README @@ -0,0 +1 @@ +This directory contains specific device bindings for KVM_CAP_DEVICE_CTRL. diff --git a/Documentation/virt/kvm/devices/arm-vgic-its.txt b/Documentation/virt/kvm/devices/arm-vgic-its.txt new file mode 100644 index 000000000000..eeaa95b893a8 --- /dev/null +++ b/Documentation/virt/kvm/devices/arm-vgic-its.txt @@ -0,0 +1,181 @@ +ARM Virtual Interrupt Translation Service (ITS) +=============================================== + +Device types supported: + KVM_DEV_TYPE_ARM_VGIC_ITS ARM Interrupt Translation Service Controller + +The ITS allows MSI(-X) interrupts to be injected into guests. This extension is +optional. Creating a virtual ITS controller also requires a host GICv3 (see +arm-vgic-v3.txt), but does not depend on having physical ITS controllers. + +There can be multiple ITS controllers per guest, each of them has to have +a separate, non-overlapping MMIO region. + + +Groups: + KVM_DEV_ARM_VGIC_GRP_ADDR + Attributes: + KVM_VGIC_ITS_ADDR_TYPE (rw, 64-bit) + Base address in the guest physical address space of the GICv3 ITS + control register frame. + This address needs to be 64K aligned and the region covers 128K. + Errors: + -E2BIG: Address outside of addressable IPA range + -EINVAL: Incorrectly aligned address + -EEXIST: Address already configured + -EFAULT: Invalid user pointer for attr->addr. + -ENODEV: Incorrect attribute or the ITS is not supported. + + + KVM_DEV_ARM_VGIC_GRP_CTRL + Attributes: + KVM_DEV_ARM_VGIC_CTRL_INIT + request the initialization of the ITS, no additional parameter in + kvm_device_attr.addr. + + KVM_DEV_ARM_ITS_CTRL_RESET + reset the ITS, no additional parameter in kvm_device_attr.addr. + See "ITS Reset State" section. + + KVM_DEV_ARM_ITS_SAVE_TABLES + save the ITS table data into guest RAM, at the location provisioned + by the guest in corresponding registers/table entries. + + The layout of the tables in guest memory defines an ABI. The entries + are laid out in little endian format as described in the last paragraph. + + KVM_DEV_ARM_ITS_RESTORE_TABLES + restore the ITS tables from guest RAM to ITS internal structures. + + The GICV3 must be restored before the ITS and all ITS registers but + the GITS_CTLR must be restored before restoring the ITS tables. + + The GITS_IIDR read-only register must also be restored before + calling KVM_DEV_ARM_ITS_RESTORE_TABLES as the IIDR revision field + encodes the ABI revision. + + The expected ordering when restoring the GICv3/ITS is described in section + "ITS Restore Sequence". + + Errors: + -ENXIO: ITS not properly configured as required prior to setting + this attribute + -ENOMEM: Memory shortage when allocating ITS internal data + -EINVAL: Inconsistent restored data + -EFAULT: Invalid guest ram access + -EBUSY: One or more VCPUS are running + -EACCES: The virtual ITS is backed by a physical GICv4 ITS, and the + state is not available + + KVM_DEV_ARM_VGIC_GRP_ITS_REGS + Attributes: + The attr field of kvm_device_attr encodes the offset of the + ITS register, relative to the ITS control frame base address + (ITS_base). + + kvm_device_attr.addr points to a __u64 value whatever the width + of the addressed register (32/64 bits). 64 bit registers can only + be accessed with full length. + + Writes to read-only registers are ignored by the kernel except for: + - GITS_CREADR. It must be restored otherwise commands in the queue + will be re-executed after restoring CWRITER. GITS_CREADR must be + restored before restoring the GITS_CTLR which is likely to enable the + ITS. Also it must be restored after GITS_CBASER since a write to + GITS_CBASER resets GITS_CREADR. + - GITS_IIDR. The Revision field encodes the table layout ABI revision. + In the future we might implement direct injection of virtual LPIs. + This will require an upgrade of the table layout and an evolution of + the ABI. GITS_IIDR must be restored before calling + KVM_DEV_ARM_ITS_RESTORE_TABLES. + + For other registers, getting or setting a register has the same + effect as reading/writing the register on real hardware. + Errors: + -ENXIO: Offset does not correspond to any supported register + -EFAULT: Invalid user pointer for attr->addr + -EINVAL: Offset is not 64-bit aligned + -EBUSY: one or more VCPUS are running + + ITS Restore Sequence: + ------------------------- + +The following ordering must be followed when restoring the GIC and the ITS: +a) restore all guest memory and create vcpus +b) restore all redistributors +c) provide the ITS base address + (KVM_DEV_ARM_VGIC_GRP_ADDR) +d) restore the ITS in the following order: + 1. Restore GITS_CBASER + 2. Restore all other GITS_ registers, except GITS_CTLR! + 3. Load the ITS table data (KVM_DEV_ARM_ITS_RESTORE_TABLES) + 4. Restore GITS_CTLR + +Then vcpus can be started. + + ITS Table ABI REV0: + ------------------- + + Revision 0 of the ABI only supports the features of a virtual GICv3, and does + not support a virtual GICv4 with support for direct injection of virtual + interrupts for nested hypervisors. + + The device table and ITT are indexed by the DeviceID and EventID, + respectively. The collection table is not indexed by CollectionID, and the + entries in the collection are listed in no particular order. + All entries are 8 bytes. + + Device Table Entry (DTE): + + bits: | 63| 62 ... 49 | 48 ... 5 | 4 ... 0 | + values: | V | next | ITT_addr | Size | + + where; + - V indicates whether the entry is valid. If not, other fields + are not meaningful. + - next: equals to 0 if this entry is the last one; otherwise it + corresponds to the DeviceID offset to the next DTE, capped by + 2^14 -1. + - ITT_addr matches bits [51:8] of the ITT address (256 Byte aligned). + - Size specifies the supported number of bits for the EventID, + minus one + + Collection Table Entry (CTE): + + bits: | 63| 62 .. 52 | 51 ... 16 | 15 ... 0 | + values: | V | RES0 | RDBase | ICID | + + where: + - V indicates whether the entry is valid. If not, other fields are + not meaningful. + - RES0: reserved field with Should-Be-Zero-or-Preserved behavior. + - RDBase is the PE number (GICR_TYPER.Processor_Number semantic), + - ICID is the collection ID + + Interrupt Translation Entry (ITE): + + bits: | 63 ... 48 | 47 ... 16 | 15 ... 0 | + values: | next | pINTID | ICID | + + where: + - next: equals to 0 if this entry is the last one; otherwise it corresponds + to the EventID offset to the next ITE capped by 2^16 -1. + - pINTID is the physical LPI ID; if zero, it means the entry is not valid + and other fields are not meaningful. + - ICID is the collection ID + + ITS Reset State: + ---------------- + +RESET returns the ITS to the same state that it was when first created and +initialized. When the RESET command returns, the following things are +guaranteed: + +- The ITS is not enabled and quiescent + GITS_CTLR.Enabled = 0 .Quiescent=1 +- There is no internally cached state +- No collection or device table are used + GITS_BASER<n>.Valid = 0 +- GITS_CBASER = 0, GITS_CREADR = 0, GITS_CWRITER = 0 +- The ABI version is unchanged and remains the one set when the ITS + device was first created. diff --git a/Documentation/virt/kvm/devices/arm-vgic-v3.txt b/Documentation/virt/kvm/devices/arm-vgic-v3.txt new file mode 100644 index 000000000000..ff290b43c8e5 --- /dev/null +++ b/Documentation/virt/kvm/devices/arm-vgic-v3.txt @@ -0,0 +1,251 @@ +ARM Virtual Generic Interrupt Controller v3 and later (VGICv3) +============================================================== + + +Device types supported: + KVM_DEV_TYPE_ARM_VGIC_V3 ARM Generic Interrupt Controller v3.0 + +Only one VGIC instance may be instantiated through this API. The created VGIC +will act as the VM interrupt controller, requiring emulated user-space devices +to inject interrupts to the VGIC instead of directly to CPUs. It is not +possible to create both a GICv3 and GICv2 on the same VM. + +Creating a guest GICv3 device requires a host GICv3 as well. + + +Groups: + KVM_DEV_ARM_VGIC_GRP_ADDR + Attributes: + KVM_VGIC_V3_ADDR_TYPE_DIST (rw, 64-bit) + Base address in the guest physical address space of the GICv3 distributor + register mappings. Only valid for KVM_DEV_TYPE_ARM_VGIC_V3. + This address needs to be 64K aligned and the region covers 64 KByte. + + KVM_VGIC_V3_ADDR_TYPE_REDIST (rw, 64-bit) + Base address in the guest physical address space of the GICv3 + redistributor register mappings. There are two 64K pages for each + VCPU and all of the redistributor pages are contiguous. + Only valid for KVM_DEV_TYPE_ARM_VGIC_V3. + This address needs to be 64K aligned. + + KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION (rw, 64-bit) + The attribute data pointed to by kvm_device_attr.addr is a __u64 value: + bits: | 63 .... 52 | 51 .... 16 | 15 - 12 |11 - 0 + values: | count | base | flags | index + - index encodes the unique redistributor region index + - flags: reserved for future use, currently 0 + - base field encodes bits [51:16] of the guest physical base address + of the first redistributor in the region. + - count encodes the number of redistributors in the region. Must be + greater than 0. + There are two 64K pages for each redistributor in the region and + redistributors are laid out contiguously within the region. Regions + are filled with redistributors in the index order. The sum of all + region count fields must be greater than or equal to the number of + VCPUs. Redistributor regions must be registered in the incremental + index order, starting from index 0. + The characteristics of a specific redistributor region can be read + by presetting the index field in the attr data. + Only valid for KVM_DEV_TYPE_ARM_VGIC_V3. + + It is invalid to mix calls with KVM_VGIC_V3_ADDR_TYPE_REDIST and + KVM_VGIC_V3_ADDR_TYPE_REDIST_REGION attributes. + + Errors: + -E2BIG: Address outside of addressable IPA range + -EINVAL: Incorrectly aligned address, bad redistributor region + count/index, mixed redistributor region attribute usage + -EEXIST: Address already configured + -ENOENT: Attempt to read the characteristics of a non existing + redistributor region + -ENXIO: The group or attribute is unknown/unsupported for this device + or hardware support is missing. + -EFAULT: Invalid user pointer for attr->addr. + + + KVM_DEV_ARM_VGIC_GRP_DIST_REGS + KVM_DEV_ARM_VGIC_GRP_REDIST_REGS + Attributes: + The attr field of kvm_device_attr encodes two values: + bits: | 63 .... 32 | 31 .... 0 | + values: | mpidr | offset | + + All distributor regs are (rw, 32-bit) and kvm_device_attr.addr points to a + __u32 value. 64-bit registers must be accessed by separately accessing the + lower and higher word. + + Writes to read-only registers are ignored by the kernel. + + KVM_DEV_ARM_VGIC_GRP_DIST_REGS accesses the main distributor registers. + KVM_DEV_ARM_VGIC_GRP_REDIST_REGS accesses the redistributor of the CPU + specified by the mpidr. + + The offset is relative to the "[Re]Distributor base address" as defined + in the GICv3/4 specs. Getting or setting such a register has the same + effect as reading or writing the register on real hardware, except for the + following registers: GICD_STATUSR, GICR_STATUSR, GICD_ISPENDR, + GICR_ISPENDR0, GICD_ICPENDR, and GICR_ICPENDR0. These registers behave + differently when accessed via this interface compared to their + architecturally defined behavior to allow software a full view of the + VGIC's internal state. + + The mpidr field is used to specify which + redistributor is accessed. The mpidr is ignored for the distributor. + + The mpidr encoding is based on the affinity information in the + architecture defined MPIDR, and the field is encoded as follows: + | 63 .... 56 | 55 .... 48 | 47 .... 40 | 39 .... 32 | + | Aff3 | Aff2 | Aff1 | Aff0 | + + Note that distributor fields are not banked, but return the same value + regardless of the mpidr used to access the register. + + GICD_IIDR.Revision is updated when the KVM implementation is changed in a + way directly observable by the guest or userspace. Userspace should read + GICD_IIDR from KVM and write back the read value to confirm its expected + behavior is aligned with the KVM implementation. Userspace should set + GICD_IIDR before setting any other registers to ensure the expected + behavior. + + + The GICD_STATUSR and GICR_STATUSR registers are architecturally defined such + that a write of a clear bit has no effect, whereas a write with a set bit + clears that value. To allow userspace to freely set the values of these two + registers, setting the attributes with the register offsets for these two + registers simply sets the non-reserved bits to the value written. + + + Accesses (reads and writes) to the GICD_ISPENDR register region and + GICR_ISPENDR0 registers get/set the value of the latched pending state for + the interrupts. + + This is identical to the value returned by a guest read from ISPENDR for an + edge triggered interrupt, but may differ for level triggered interrupts. + For edge triggered interrupts, once an interrupt becomes pending (whether + because of an edge detected on the input line or because of a guest write + to ISPENDR) this state is "latched", and only cleared when either the + interrupt is activated or when the guest writes to ICPENDR. A level + triggered interrupt may be pending either because the level input is held + high by a device, or because of a guest write to the ISPENDR register. Only + ISPENDR writes are latched; if the device lowers the line level then the + interrupt is no longer pending unless the guest also wrote to ISPENDR, and + conversely writes to ICPENDR or activations of the interrupt do not clear + the pending status if the line level is still being held high. (These + rules are documented in the GICv3 specification descriptions of the ICPENDR + and ISPENDR registers.) For a level triggered interrupt the value accessed + here is that of the latch which is set by ISPENDR and cleared by ICPENDR or + interrupt activation, whereas the value returned by a guest read from + ISPENDR is the logical OR of the latch value and the input line level. + + Raw access to the latch state is provided to userspace so that it can save + and restore the entire GIC internal state (which is defined by the + combination of the current input line level and the latch state, and cannot + be deduced from purely the line level and the value of the ISPENDR + registers). + + Accesses to GICD_ICPENDR register region and GICR_ICPENDR0 registers have + RAZ/WI semantics, meaning that reads always return 0 and writes are always + ignored. + + Errors: + -ENXIO: Getting or setting this register is not yet supported + -EBUSY: One or more VCPUs are running + + + KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS + Attributes: + The attr field of kvm_device_attr encodes two values: + bits: | 63 .... 32 | 31 .... 16 | 15 .... 0 | + values: | mpidr | RES | instr | + + The mpidr field encodes the CPU ID based on the affinity information in the + architecture defined MPIDR, and the field is encoded as follows: + | 63 .... 56 | 55 .... 48 | 47 .... 40 | 39 .... 32 | + | Aff3 | Aff2 | Aff1 | Aff0 | + + The instr field encodes the system register to access based on the fields + defined in the A64 instruction set encoding for system register access + (RES means the bits are reserved for future use and should be zero): + + | 15 ... 14 | 13 ... 11 | 10 ... 7 | 6 ... 3 | 2 ... 0 | + | Op 0 | Op1 | CRn | CRm | Op2 | + + All system regs accessed through this API are (rw, 64-bit) and + kvm_device_attr.addr points to a __u64 value. + + KVM_DEV_ARM_VGIC_GRP_CPU_SYSREGS accesses the CPU interface registers for the + CPU specified by the mpidr field. + + CPU interface registers access is not implemented for AArch32 mode. + Error -ENXIO is returned when accessed in AArch32 mode. + Errors: + -ENXIO: Getting or setting this register is not yet supported + -EBUSY: VCPU is running + -EINVAL: Invalid mpidr or register value supplied + + + KVM_DEV_ARM_VGIC_GRP_NR_IRQS + Attributes: + A value describing the number of interrupts (SGI, PPI and SPI) for + this GIC instance, ranging from 64 to 1024, in increments of 32. + + kvm_device_attr.addr points to a __u32 value. + + Errors: + -EINVAL: Value set is out of the expected range + -EBUSY: Value has already be set. + + + KVM_DEV_ARM_VGIC_GRP_CTRL + Attributes: + KVM_DEV_ARM_VGIC_CTRL_INIT + request the initialization of the VGIC, no additional parameter in + kvm_device_attr.addr. + KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES + save all LPI pending bits into guest RAM pending tables. + + The first kB of the pending table is not altered by this operation. + Errors: + -ENXIO: VGIC not properly configured as required prior to calling + this attribute + -ENODEV: no online VCPU + -ENOMEM: memory shortage when allocating vgic internal data + -EFAULT: Invalid guest ram access + -EBUSY: One or more VCPUS are running + + + KVM_DEV_ARM_VGIC_GRP_LEVEL_INFO + Attributes: + The attr field of kvm_device_attr encodes the following values: + bits: | 63 .... 32 | 31 .... 10 | 9 .... 0 | + values: | mpidr | info | vINTID | + + The vINTID specifies which set of IRQs is reported on. + + The info field specifies which information userspace wants to get or set + using this interface. Currently we support the following info values: + + VGIC_LEVEL_INFO_LINE_LEVEL: + Get/Set the input level of the IRQ line for a set of 32 contiguously + numbered interrupts. + vINTID must be a multiple of 32. + + kvm_device_attr.addr points to a __u32 value which will contain a + bitmap where a set bit means the interrupt level is asserted. + + Bit[n] indicates the status for interrupt vINTID + n. + + SGIs and any interrupt with a higher ID than the number of interrupts + supported, will be RAZ/WI. LPIs are always edge-triggered and are + therefore not supported by this interface. + + PPIs are reported per VCPU as specified in the mpidr field, and SPIs are + reported with the same value regardless of the mpidr specified. + + The mpidr field encodes the CPU ID based on the affinity information in the + architecture defined MPIDR, and the field is encoded as follows: + | 63 .... 56 | 55 .... 48 | 47 .... 40 | 39 .... 32 | + | Aff3 | Aff2 | Aff1 | Aff0 | + Errors: + -EINVAL: vINTID is not multiple of 32 or + info field is not VGIC_LEVEL_INFO_LINE_LEVEL diff --git a/Documentation/virt/kvm/devices/arm-vgic.txt b/Documentation/virt/kvm/devices/arm-vgic.txt new file mode 100644 index 000000000000..97b6518148f8 --- /dev/null +++ b/Documentation/virt/kvm/devices/arm-vgic.txt @@ -0,0 +1,127 @@ +ARM Virtual Generic Interrupt Controller v2 (VGIC) +================================================== + +Device types supported: + KVM_DEV_TYPE_ARM_VGIC_V2 ARM Generic Interrupt Controller v2.0 + +Only one VGIC instance may be instantiated through either this API or the +legacy KVM_CREATE_IRQCHIP API. The created VGIC will act as the VM interrupt +controller, requiring emulated user-space devices to inject interrupts to the +VGIC instead of directly to CPUs. + +GICv3 implementations with hardware compatibility support allow creating a +guest GICv2 through this interface. For information on creating a guest GICv3 +device and guest ITS devices, see arm-vgic-v3.txt. It is not possible to +create both a GICv3 and GICv2 device on the same VM. + + +Groups: + KVM_DEV_ARM_VGIC_GRP_ADDR + Attributes: + KVM_VGIC_V2_ADDR_TYPE_DIST (rw, 64-bit) + Base address in the guest physical address space of the GIC distributor + register mappings. Only valid for KVM_DEV_TYPE_ARM_VGIC_V2. + This address needs to be 4K aligned and the region covers 4 KByte. + + KVM_VGIC_V2_ADDR_TYPE_CPU (rw, 64-bit) + Base address in the guest physical address space of the GIC virtual cpu + interface register mappings. Only valid for KVM_DEV_TYPE_ARM_VGIC_V2. + This address needs to be 4K aligned and the region covers 4 KByte. + Errors: + -E2BIG: Address outside of addressable IPA range + -EINVAL: Incorrectly aligned address + -EEXIST: Address already configured + -ENXIO: The group or attribute is unknown/unsupported for this device + or hardware support is missing. + -EFAULT: Invalid user pointer for attr->addr. + + KVM_DEV_ARM_VGIC_GRP_DIST_REGS + Attributes: + The attr field of kvm_device_attr encodes two values: + bits: | 63 .... 40 | 39 .. 32 | 31 .... 0 | + values: | reserved | vcpu_index | offset | + + All distributor regs are (rw, 32-bit) + + The offset is relative to the "Distributor base address" as defined in the + GICv2 specs. Getting or setting such a register has the same effect as + reading or writing the register on the actual hardware from the cpu whose + index is specified with the vcpu_index field. Note that most distributor + fields are not banked, but return the same value regardless of the + vcpu_index used to access the register. + + GICD_IIDR.Revision is updated when the KVM implementation of an emulated + GICv2 is changed in a way directly observable by the guest or userspace. + Userspace should read GICD_IIDR from KVM and write back the read value to + confirm its expected behavior is aligned with the KVM implementation. + Userspace should set GICD_IIDR before setting any other registers (both + KVM_DEV_ARM_VGIC_GRP_DIST_REGS and KVM_DEV_ARM_VGIC_GRP_CPU_REGS) to ensure + the expected behavior. Unless GICD_IIDR has been set from userspace, writes + to the interrupt group registers (GICD_IGROUPR) are ignored. + Errors: + -ENXIO: Getting or setting this register is not yet supported + -EBUSY: One or more VCPUs are running + -EINVAL: Invalid vcpu_index supplied + + KVM_DEV_ARM_VGIC_GRP_CPU_REGS + Attributes: + The attr field of kvm_device_attr encodes two values: + bits: | 63 .... 40 | 39 .. 32 | 31 .... 0 | + values: | reserved | vcpu_index | offset | + + All CPU interface regs are (rw, 32-bit) + + The offset specifies the offset from the "CPU interface base address" as + defined in the GICv2 specs. Getting or setting such a register has the + same effect as reading or writing the register on the actual hardware. + + The Active Priorities Registers APRn are implementation defined, so we set a + fixed format for our implementation that fits with the model of a "GICv2 + implementation without the security extensions" which we present to the + guest. This interface always exposes four register APR[0-3] describing the + maximum possible 128 preemption levels. The semantics of the register + indicate if any interrupts in a given preemption level are in the active + state by setting the corresponding bit. + + Thus, preemption level X has one or more active interrupts if and only if: + + APRn[X mod 32] == 0b1, where n = X / 32 + + Bits for undefined preemption levels are RAZ/WI. + + Note that this differs from a CPU's view of the APRs on hardware in which + a GIC without the security extensions expose group 0 and group 1 active + priorities in separate register groups, whereas we show a combined view + similar to GICv2's GICH_APR. + + For historical reasons and to provide ABI compatibility with userspace we + export the GICC_PMR register in the format of the GICH_VMCR.VMPriMask + field in the lower 5 bits of a word, meaning that userspace must always + use the lower 5 bits to communicate with the KVM device and must shift the + value left by 3 places to obtain the actual priority mask level. + + Errors: + -ENXIO: Getting or setting this register is not yet supported + -EBUSY: One or more VCPUs are running + -EINVAL: Invalid vcpu_index supplied + + KVM_DEV_ARM_VGIC_GRP_NR_IRQS + Attributes: + A value describing the number of interrupts (SGI, PPI and SPI) for + this GIC instance, ranging from 64 to 1024, in increments of 32. + + Errors: + -EINVAL: Value set is out of the expected range + -EBUSY: Value has already be set, or GIC has already been initialized + with default values. + + KVM_DEV_ARM_VGIC_GRP_CTRL + Attributes: + KVM_DEV_ARM_VGIC_CTRL_INIT + request the initialization of the VGIC or ITS, no additional parameter + in kvm_device_attr.addr. + Errors: + -ENXIO: VGIC not properly configured as required prior to calling + this attribute + -ENODEV: no online VCPU + -ENOMEM: memory shortage when allocating vgic internal data diff --git a/Documentation/virt/kvm/devices/mpic.txt b/Documentation/virt/kvm/devices/mpic.txt new file mode 100644 index 000000000000..8257397adc3c --- /dev/null +++ b/Documentation/virt/kvm/devices/mpic.txt @@ -0,0 +1,53 @@ +MPIC interrupt controller +========================= + +Device types supported: + KVM_DEV_TYPE_FSL_MPIC_20 Freescale MPIC v2.0 + KVM_DEV_TYPE_FSL_MPIC_42 Freescale MPIC v4.2 + +Only one MPIC instance, of any type, may be instantiated. The created +MPIC will act as the system interrupt controller, connecting to each +vcpu's interrupt inputs. + +Groups: + KVM_DEV_MPIC_GRP_MISC + Attributes: + KVM_DEV_MPIC_BASE_ADDR (rw, 64-bit) + Base address of the 256 KiB MPIC register space. Must be + naturally aligned. A value of zero disables the mapping. + Reset value is zero. + + KVM_DEV_MPIC_GRP_REGISTER (rw, 32-bit) + Access an MPIC register, as if the access were made from the guest. + "attr" is the byte offset into the MPIC register space. Accesses + must be 4-byte aligned. + + MSIs may be signaled by using this attribute group to write + to the relevant MSIIR. + + KVM_DEV_MPIC_GRP_IRQ_ACTIVE (rw, 32-bit) + IRQ input line for each standard openpic source. 0 is inactive and 1 + is active, regardless of interrupt sense. + + For edge-triggered interrupts: Writing 1 is considered an activating + edge, and writing 0 is ignored. Reading returns 1 if a previously + signaled edge has not been acknowledged, and 0 otherwise. + + "attr" is the IRQ number. IRQ numbers for standard sources are the + byte offset of the relevant IVPR from EIVPR0, divided by 32. + +IRQ Routing: + + The MPIC emulation supports IRQ routing. Only a single MPIC device can + be instantiated. Once that device has been created, it's available as + irqchip id 0. + + This irqchip 0 has 256 interrupt pins, which expose the interrupts in + the main array of interrupt sources (a.k.a. "SRC" interrupts). + + The numbering is the same as the MPIC device tree binding -- based on + the register offset from the beginning of the sources array, without + regard to any subdivisions in chip documentation such as "internal" + or "external" interrupts. + + Access to non-SRC interrupts is not implemented through IRQ routing mechanisms. diff --git a/Documentation/virt/kvm/devices/s390_flic.txt b/Documentation/virt/kvm/devices/s390_flic.txt new file mode 100644 index 000000000000..a4e20a090174 --- /dev/null +++ b/Documentation/virt/kvm/devices/s390_flic.txt @@ -0,0 +1,163 @@ +FLIC (floating interrupt controller) +==================================== + +FLIC handles floating (non per-cpu) interrupts, i.e. I/O, service and some +machine check interruptions. All interrupts are stored in a per-vm list of +pending interrupts. FLIC performs operations on this list. + +Only one FLIC instance may be instantiated. + +FLIC provides support to +- add interrupts (KVM_DEV_FLIC_ENQUEUE) +- inspect currently pending interrupts (KVM_FLIC_GET_ALL_IRQS) +- purge all pending floating interrupts (KVM_DEV_FLIC_CLEAR_IRQS) +- purge one pending floating I/O interrupt (KVM_DEV_FLIC_CLEAR_IO_IRQ) +- enable/disable for the guest transparent async page faults +- register and modify adapter interrupt sources (KVM_DEV_FLIC_ADAPTER_*) +- modify AIS (adapter-interruption-suppression) mode state (KVM_DEV_FLIC_AISM) +- inject adapter interrupts on a specified adapter (KVM_DEV_FLIC_AIRQ_INJECT) +- get/set all AIS mode states (KVM_DEV_FLIC_AISM_ALL) + +Groups: + KVM_DEV_FLIC_ENQUEUE + Passes a buffer and length into the kernel which are then injected into + the list of pending interrupts. + attr->addr contains the pointer to the buffer and attr->attr contains + the length of the buffer. + The format of the data structure kvm_s390_irq as it is copied from userspace + is defined in usr/include/linux/kvm.h. + + KVM_DEV_FLIC_GET_ALL_IRQS + Copies all floating interrupts into a buffer provided by userspace. + When the buffer is too small it returns -ENOMEM, which is the indication + for userspace to try again with a bigger buffer. + -ENOBUFS is returned when the allocation of a kernelspace buffer has + failed. + -EFAULT is returned when copying data to userspace failed. + All interrupts remain pending, i.e. are not deleted from the list of + currently pending interrupts. + attr->addr contains the userspace address of the buffer into which all + interrupt data will be copied. + attr->attr contains the size of the buffer in bytes. + + KVM_DEV_FLIC_CLEAR_IRQS + Simply deletes all elements from the list of currently pending floating + interrupts. No interrupts are injected into the guest. + + KVM_DEV_FLIC_CLEAR_IO_IRQ + Deletes one (if any) I/O interrupt for a subchannel identified by the + subsystem identification word passed via the buffer specified by + attr->addr (address) and attr->attr (length). + + KVM_DEV_FLIC_APF_ENABLE + Enables async page faults for the guest. So in case of a major page fault + the host is allowed to handle this async and continues the guest. + + KVM_DEV_FLIC_APF_DISABLE_WAIT + Disables async page faults for the guest and waits until already pending + async page faults are done. This is necessary to trigger a completion interrupt + for every init interrupt before migrating the interrupt list. + + KVM_DEV_FLIC_ADAPTER_REGISTER + Register an I/O adapter interrupt source. Takes a kvm_s390_io_adapter + describing the adapter to register: + +struct kvm_s390_io_adapter { + __u32 id; + __u8 isc; + __u8 maskable; + __u8 swap; + __u8 flags; +}; + + id contains the unique id for the adapter, isc the I/O interruption subclass + to use, maskable whether this adapter may be masked (interrupts turned off), + swap whether the indicators need to be byte swapped, and flags contains + further characteristics of the adapter. + Currently defined values for 'flags' are: + - KVM_S390_ADAPTER_SUPPRESSIBLE: adapter is subject to AIS + (adapter-interrupt-suppression) facility. This flag only has an effect if + the AIS capability is enabled. + Unknown flag values are ignored. + + + KVM_DEV_FLIC_ADAPTER_MODIFY + Modifies attributes of an existing I/O adapter interrupt source. Takes + a kvm_s390_io_adapter_req specifying the adapter and the operation: + +struct kvm_s390_io_adapter_req { + __u32 id; + __u8 type; + __u8 mask; + __u16 pad0; + __u64 addr; +}; + + id specifies the adapter and type the operation. The supported operations + are: + + KVM_S390_IO_ADAPTER_MASK + mask or unmask the adapter, as specified in mask + + KVM_S390_IO_ADAPTER_MAP + perform a gmap translation for the guest address provided in addr, + pin a userspace page for the translated address and add it to the + list of mappings + Note: A new mapping will be created unconditionally; therefore, + the calling code should avoid making duplicate mappings. + + KVM_S390_IO_ADAPTER_UNMAP + release a userspace page for the translated address specified in addr + from the list of mappings + + KVM_DEV_FLIC_AISM + modify the adapter-interruption-suppression mode for a given isc if the + AIS capability is enabled. Takes a kvm_s390_ais_req describing: + +struct kvm_s390_ais_req { + __u8 isc; + __u16 mode; +}; + + isc contains the target I/O interruption subclass, mode the target + adapter-interruption-suppression mode. The following modes are + currently supported: + - KVM_S390_AIS_MODE_ALL: ALL-Interruptions Mode, i.e. airq injection + is always allowed; + - KVM_S390_AIS_MODE_SINGLE: SINGLE-Interruption Mode, i.e. airq + injection is only allowed once and the following adapter interrupts + will be suppressed until the mode is set again to ALL-Interruptions + or SINGLE-Interruption mode. + + KVM_DEV_FLIC_AIRQ_INJECT + Inject adapter interrupts on a specified adapter. + attr->attr contains the unique id for the adapter, which allows for + adapter-specific checks and actions. + For adapters subject to AIS, handle the airq injection suppression for + an isc according to the adapter-interruption-suppression mode on condition + that the AIS capability is enabled. + + KVM_DEV_FLIC_AISM_ALL + Gets or sets the adapter-interruption-suppression mode for all ISCs. Takes + a kvm_s390_ais_all describing: + +struct kvm_s390_ais_all { + __u8 simm; /* Single-Interruption-Mode mask */ + __u8 nimm; /* No-Interruption-Mode mask * +}; + + simm contains Single-Interruption-Mode mask for all ISCs, nimm contains + No-Interruption-Mode mask for all ISCs. Each bit in simm and nimm corresponds + to an ISC (MSB0 bit 0 to ISC 0 and so on). The combination of simm bit and + nimm bit presents AIS mode for a ISC. + + KVM_DEV_FLIC_AISM_ALL is indicated by KVM_CAP_S390_AIS_MIGRATION. + +Note: The KVM_SET_DEVICE_ATTR/KVM_GET_DEVICE_ATTR device ioctls executed on +FLIC with an unknown group or attribute gives the error code EINVAL (instead of +ENXIO, as specified in the API documentation). It is not possible to conclude +that a FLIC operation is unavailable based on the error code resulting from a +usage attempt. + +Note: The KVM_DEV_FLIC_CLEAR_IO_IRQ ioctl will return EINVAL in case a zero +schid is specified. diff --git a/Documentation/virt/kvm/devices/vcpu.txt b/Documentation/virt/kvm/devices/vcpu.txt new file mode 100644 index 000000000000..2b5dab16c4f2 --- /dev/null +++ b/Documentation/virt/kvm/devices/vcpu.txt @@ -0,0 +1,62 @@ +Generic vcpu interface +==================================== + +The virtual cpu "device" also accepts the ioctls KVM_SET_DEVICE_ATTR, +KVM_GET_DEVICE_ATTR, and KVM_HAS_DEVICE_ATTR. The interface uses the same struct +kvm_device_attr as other devices, but targets VCPU-wide settings and controls. + +The groups and attributes per virtual cpu, if any, are architecture specific. + +1. GROUP: KVM_ARM_VCPU_PMU_V3_CTRL +Architectures: ARM64 + +1.1. ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_IRQ +Parameters: in kvm_device_attr.addr the address for PMU overflow interrupt is a + pointer to an int +Returns: -EBUSY: The PMU overflow interrupt is already set + -ENXIO: The overflow interrupt not set when attempting to get it + -ENODEV: PMUv3 not supported + -EINVAL: Invalid PMU overflow interrupt number supplied or + trying to set the IRQ number without using an in-kernel + irqchip. + +A value describing the PMUv3 (Performance Monitor Unit v3) overflow interrupt +number for this vcpu. This interrupt could be a PPI or SPI, but the interrupt +type must be same for each vcpu. As a PPI, the interrupt number is the same for +all vcpus, while as an SPI it must be a separate number per vcpu. + +1.2 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_INIT +Parameters: no additional parameter in kvm_device_attr.addr +Returns: -ENODEV: PMUv3 not supported or GIC not initialized + -ENXIO: PMUv3 not properly configured or in-kernel irqchip not + configured as required prior to calling this attribute + -EBUSY: PMUv3 already initialized + +Request the initialization of the PMUv3. If using the PMUv3 with an in-kernel +virtual GIC implementation, this must be done after initializing the in-kernel +irqchip. + + +2. GROUP: KVM_ARM_VCPU_TIMER_CTRL +Architectures: ARM,ARM64 + +2.1. ATTRIBUTE: KVM_ARM_VCPU_TIMER_IRQ_VTIMER +2.2. ATTRIBUTE: KVM_ARM_VCPU_TIMER_IRQ_PTIMER +Parameters: in kvm_device_attr.addr the address for the timer interrupt is a + pointer to an int +Returns: -EINVAL: Invalid timer interrupt number + -EBUSY: One or more VCPUs has already run + +A value describing the architected timer interrupt number when connected to an +in-kernel virtual GIC. These must be a PPI (16 <= intid < 32). Setting the +attribute overrides the default values (see below). + +KVM_ARM_VCPU_TIMER_IRQ_VTIMER: The EL1 virtual timer intid (default: 27) +KVM_ARM_VCPU_TIMER_IRQ_PTIMER: The EL1 physical timer intid (default: 30) + +Setting the same PPI for different timers will prevent the VCPUs from running. +Setting the interrupt number on a VCPU configures all VCPUs created at that +time to use the number provided for a given timer, overwriting any previously +configured values on other VCPUs. Userspace should configure the interrupt +numbers on at least one VCPU after creating all VCPUs and before running any +VCPUs. diff --git a/Documentation/virt/kvm/devices/vfio.txt b/Documentation/virt/kvm/devices/vfio.txt new file mode 100644 index 000000000000..528c77c8022c --- /dev/null +++ b/Documentation/virt/kvm/devices/vfio.txt @@ -0,0 +1,36 @@ +VFIO virtual device +=================== + +Device types supported: + KVM_DEV_TYPE_VFIO + +Only one VFIO instance may be created per VM. The created device +tracks VFIO groups in use by the VM and features of those groups +important to the correctness and acceleration of the VM. As groups +are enabled and disabled for use by the VM, KVM should be updated +about their presence. When registered with KVM, a reference to the +VFIO-group is held by KVM. + +Groups: + KVM_DEV_VFIO_GROUP + +KVM_DEV_VFIO_GROUP attributes: + KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking + kvm_device_attr.addr points to an int32_t file descriptor + for the VFIO group. + KVM_DEV_VFIO_GROUP_DEL: Remove a VFIO group from VFIO-KVM device tracking + kvm_device_attr.addr points to an int32_t file descriptor + for the VFIO group. + KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE: attaches a guest visible TCE table + allocated by sPAPR KVM. + kvm_device_attr.addr points to a struct: + + struct kvm_vfio_spapr_tce { + __s32 groupfd; + __s32 tablefd; + }; + + where + @groupfd is a file descriptor for a VFIO group; + @tablefd is a file descriptor for a TCE table allocated via + KVM_CREATE_SPAPR_TCE. diff --git a/Documentation/virt/kvm/devices/vm.txt b/Documentation/virt/kvm/devices/vm.txt new file mode 100644 index 000000000000..4ffb82b02468 --- /dev/null +++ b/Documentation/virt/kvm/devices/vm.txt @@ -0,0 +1,270 @@ +Generic vm interface +==================================== + +The virtual machine "device" also accepts the ioctls KVM_SET_DEVICE_ATTR, +KVM_GET_DEVICE_ATTR, and KVM_HAS_DEVICE_ATTR. The interface uses the same +struct kvm_device_attr as other devices, but targets VM-wide settings +and controls. + +The groups and attributes per virtual machine, if any, are architecture +specific. + +1. GROUP: KVM_S390_VM_MEM_CTRL +Architectures: s390 + +1.1. ATTRIBUTE: KVM_S390_VM_MEM_ENABLE_CMMA +Parameters: none +Returns: -EBUSY if a vcpu is already defined, otherwise 0 + +Enables Collaborative Memory Management Assist (CMMA) for the virtual machine. + +1.2. ATTRIBUTE: KVM_S390_VM_MEM_CLR_CMMA +Parameters: none +Returns: -EINVAL if CMMA was not enabled + 0 otherwise + +Clear the CMMA status for all guest pages, so any pages the guest marked +as unused are again used any may not be reclaimed by the host. + +1.3. ATTRIBUTE KVM_S390_VM_MEM_LIMIT_SIZE +Parameters: in attr->addr the address for the new limit of guest memory +Returns: -EFAULT if the given address is not accessible + -EINVAL if the virtual machine is of type UCONTROL + -E2BIG if the given guest memory is to big for that machine + -EBUSY if a vcpu is already defined + -ENOMEM if not enough memory is available for a new shadow guest mapping + 0 otherwise + +Allows userspace to query the actual limit and set a new limit for +the maximum guest memory size. The limit will be rounded up to +2048 MB, 4096 GB, 8192 TB respectively, as this limit is governed by +the number of page table levels. In the case that there is no limit we will set +the limit to KVM_S390_NO_MEM_LIMIT (U64_MAX). + +2. GROUP: KVM_S390_VM_CPU_MODEL +Architectures: s390 + +2.1. ATTRIBUTE: KVM_S390_VM_CPU_MACHINE (r/o) + +Allows user space to retrieve machine and kvm specific cpu related information: + +struct kvm_s390_vm_cpu_machine { + __u64 cpuid; # CPUID of host + __u32 ibc; # IBC level range offered by host + __u8 pad[4]; + __u64 fac_mask[256]; # set of cpu facilities enabled by KVM + __u64 fac_list[256]; # set of cpu facilities offered by host +} + +Parameters: address of buffer to store the machine related cpu data + of type struct kvm_s390_vm_cpu_machine* +Returns: -EFAULT if the given address is not accessible from kernel space + -ENOMEM if not enough memory is available to process the ioctl + 0 in case of success + +2.2. ATTRIBUTE: KVM_S390_VM_CPU_PROCESSOR (r/w) + +Allows user space to retrieve or request to change cpu related information for a vcpu: + +struct kvm_s390_vm_cpu_processor { + __u64 cpuid; # CPUID currently (to be) used by this vcpu + __u16 ibc; # IBC level currently (to be) used by this vcpu + __u8 pad[6]; + __u64 fac_list[256]; # set of cpu facilities currently (to be) used + # by this vcpu +} + +KVM does not enforce or limit the cpu model data in any form. Take the information +retrieved by means of KVM_S390_VM_CPU_MACHINE as hint for reasonable configuration +setups. Instruction interceptions triggered by additionally set facility bits that +are not handled by KVM need to by imlemented in the VM driver code. + +Parameters: address of buffer to store/set the processor related cpu + data of type struct kvm_s390_vm_cpu_processor*. +Returns: -EBUSY in case 1 or more vcpus are already activated (only in write case) + -EFAULT if the given address is not accessible from kernel space + -ENOMEM if not enough memory is available to process the ioctl + 0 in case of success + +2.3. ATTRIBUTE: KVM_S390_VM_CPU_MACHINE_FEAT (r/o) + +Allows user space to retrieve available cpu features. A feature is available if +provided by the hardware and supported by kvm. In theory, cpu features could +even be completely emulated by kvm. + +struct kvm_s390_vm_cpu_feat { + __u64 feat[16]; # Bitmap (1 = feature available), MSB 0 bit numbering +}; + +Parameters: address of a buffer to load the feature list from. +Returns: -EFAULT if the given address is not accessible from kernel space. + 0 in case of success. + +2.4. ATTRIBUTE: KVM_S390_VM_CPU_PROCESSOR_FEAT (r/w) + +Allows user space to retrieve or change enabled cpu features for all VCPUs of a +VM. Features that are not available cannot be enabled. + +See 2.3. for a description of the parameter struct. + +Parameters: address of a buffer to store/load the feature list from. +Returns: -EFAULT if the given address is not accessible from kernel space. + -EINVAL if a cpu feature that is not available is to be enabled. + -EBUSY if at least one VCPU has already been defined. + 0 in case of success. + +2.5. ATTRIBUTE: KVM_S390_VM_CPU_MACHINE_SUBFUNC (r/o) + +Allows user space to retrieve available cpu subfunctions without any filtering +done by a set IBC. These subfunctions are indicated to the guest VCPU via +query or "test bit" subfunctions and used e.g. by cpacf functions, plo and ptff. + +A subfunction block is only valid if KVM_S390_VM_CPU_MACHINE contains the +STFL(E) bit introducing the affected instruction. If the affected instruction +indicates subfunctions via a "query subfunction", the response block is +contained in the returned struct. If the affected instruction +indicates subfunctions via a "test bit" mechanism, the subfunction codes are +contained in the returned struct in MSB 0 bit numbering. + +struct kvm_s390_vm_cpu_subfunc { + u8 plo[32]; # always valid (ESA/390 feature) + u8 ptff[16]; # valid with TOD-clock steering + u8 kmac[16]; # valid with Message-Security-Assist + u8 kmc[16]; # valid with Message-Security-Assist + u8 km[16]; # valid with Message-Security-Assist + u8 kimd[16]; # valid with Message-Security-Assist + u8 klmd[16]; # valid with Message-Security-Assist + u8 pckmo[16]; # valid with Message-Security-Assist-Extension 3 + u8 kmctr[16]; # valid with Message-Security-Assist-Extension 4 + u8 kmf[16]; # valid with Message-Security-Assist-Extension 4 + u8 kmo[16]; # valid with Message-Security-Assist-Extension 4 + u8 pcc[16]; # valid with Message-Security-Assist-Extension 4 + u8 ppno[16]; # valid with Message-Security-Assist-Extension 5 + u8 kma[16]; # valid with Message-Security-Assist-Extension 8 + u8 kdsa[16]; # valid with Message-Security-Assist-Extension 9 + u8 reserved[1792]; # reserved for future instructions +}; + +Parameters: address of a buffer to load the subfunction blocks from. +Returns: -EFAULT if the given address is not accessible from kernel space. + 0 in case of success. + +2.6. ATTRIBUTE: KVM_S390_VM_CPU_PROCESSOR_SUBFUNC (r/w) + +Allows user space to retrieve or change cpu subfunctions to be indicated for +all VCPUs of a VM. This attribute will only be available if kernel and +hardware support are in place. + +The kernel uses the configured subfunction blocks for indication to +the guest. A subfunction block will only be used if the associated STFL(E) bit +has not been disabled by user space (so the instruction to be queried is +actually available for the guest). + +As long as no data has been written, a read will fail. The IBC will be used +to determine available subfunctions in this case, this will guarantee backward +compatibility. + +See 2.5. for a description of the parameter struct. + +Parameters: address of a buffer to store/load the subfunction blocks from. +Returns: -EFAULT if the given address is not accessible from kernel space. + -EINVAL when reading, if there was no write yet. + -EBUSY if at least one VCPU has already been defined. + 0 in case of success. + +3. GROUP: KVM_S390_VM_TOD +Architectures: s390 + +3.1. ATTRIBUTE: KVM_S390_VM_TOD_HIGH + +Allows user space to set/get the TOD clock extension (u8) (superseded by +KVM_S390_VM_TOD_EXT). + +Parameters: address of a buffer in user space to store the data (u8) to +Returns: -EFAULT if the given address is not accessible from kernel space + -EINVAL if setting the TOD clock extension to != 0 is not supported + +3.2. ATTRIBUTE: KVM_S390_VM_TOD_LOW + +Allows user space to set/get bits 0-63 of the TOD clock register as defined in +the POP (u64). + +Parameters: address of a buffer in user space to store the data (u64) to +Returns: -EFAULT if the given address is not accessible from kernel space + +3.3. ATTRIBUTE: KVM_S390_VM_TOD_EXT +Allows user space to set/get bits 0-63 of the TOD clock register as defined in +the POP (u64). If the guest CPU model supports the TOD clock extension (u8), it +also allows user space to get/set it. If the guest CPU model does not support +it, it is stored as 0 and not allowed to be set to a value != 0. + +Parameters: address of a buffer in user space to store the data + (kvm_s390_vm_tod_clock) to +Returns: -EFAULT if the given address is not accessible from kernel space + -EINVAL if setting the TOD clock extension to != 0 is not supported + +4. GROUP: KVM_S390_VM_CRYPTO +Architectures: s390 + +4.1. ATTRIBUTE: KVM_S390_VM_CRYPTO_ENABLE_AES_KW (w/o) + +Allows user space to enable aes key wrapping, including generating a new +wrapping key. + +Parameters: none +Returns: 0 + +4.2. ATTRIBUTE: KVM_S390_VM_CRYPTO_ENABLE_DEA_KW (w/o) + +Allows user space to enable dea key wrapping, including generating a new +wrapping key. + +Parameters: none +Returns: 0 + +4.3. ATTRIBUTE: KVM_S390_VM_CRYPTO_DISABLE_AES_KW (w/o) + +Allows user space to disable aes key wrapping, clearing the wrapping key. + +Parameters: none +Returns: 0 + +4.4. ATTRIBUTE: KVM_S390_VM_CRYPTO_DISABLE_DEA_KW (w/o) + +Allows user space to disable dea key wrapping, clearing the wrapping key. + +Parameters: none +Returns: 0 + +5. GROUP: KVM_S390_VM_MIGRATION +Architectures: s390 + +5.1. ATTRIBUTE: KVM_S390_VM_MIGRATION_STOP (w/o) + +Allows userspace to stop migration mode, needed for PGSTE migration. +Setting this attribute when migration mode is not active will have no +effects. + +Parameters: none +Returns: 0 + +5.2. ATTRIBUTE: KVM_S390_VM_MIGRATION_START (w/o) + +Allows userspace to start migration mode, needed for PGSTE migration. +Setting this attribute when migration mode is already active will have +no effects. + +Parameters: none +Returns: -ENOMEM if there is not enough free memory to start migration mode + -EINVAL if the state of the VM is invalid (e.g. no memory defined) + 0 in case of success. + +5.3. ATTRIBUTE: KVM_S390_VM_MIGRATION_STATUS (r/o) + +Allows userspace to query the status of migration mode. + +Parameters: address of a buffer in user space to store the data (u64) to; + the data itself is either 0 if migration mode is disabled or 1 + if it is enabled +Returns: -EFAULT if the given address is not accessible from kernel space + 0 in case of success. diff --git a/Documentation/virt/kvm/devices/xics.txt b/Documentation/virt/kvm/devices/xics.txt new file mode 100644 index 000000000000..42864935ac5d --- /dev/null +++ b/Documentation/virt/kvm/devices/xics.txt @@ -0,0 +1,66 @@ +XICS interrupt controller + +Device type supported: KVM_DEV_TYPE_XICS + +Groups: + KVM_DEV_XICS_SOURCES + Attributes: One per interrupt source, indexed by the source number. + +This device emulates the XICS (eXternal Interrupt Controller +Specification) defined in PAPR. The XICS has a set of interrupt +sources, each identified by a 20-bit source number, and a set of +Interrupt Control Presentation (ICP) entities, also called "servers", +each associated with a virtual CPU. + +The ICP entities are created by enabling the KVM_CAP_IRQ_ARCH +capability for each vcpu, specifying KVM_CAP_IRQ_XICS in args[0] and +the interrupt server number (i.e. the vcpu number from the XICS's +point of view) in args[1] of the kvm_enable_cap struct. Each ICP has +64 bits of state which can be read and written using the +KVM_GET_ONE_REG and KVM_SET_ONE_REG ioctls on the vcpu. The 64 bit +state word has the following bitfields, starting at the +least-significant end of the word: + +* Unused, 16 bits + +* Pending interrupt priority, 8 bits + Zero is the highest priority, 255 means no interrupt is pending. + +* Pending IPI (inter-processor interrupt) priority, 8 bits + Zero is the highest priority, 255 means no IPI is pending. + +* Pending interrupt source number, 24 bits + Zero means no interrupt pending, 2 means an IPI is pending + +* Current processor priority, 8 bits + Zero is the highest priority, meaning no interrupts can be + delivered, and 255 is the lowest priority. + +Each source has 64 bits of state that can be read and written using +the KVM_GET_DEVICE_ATTR and KVM_SET_DEVICE_ATTR ioctls, specifying the +KVM_DEV_XICS_SOURCES attribute group, with the attribute number being +the interrupt source number. The 64 bit state word has the following +bitfields, starting from the least-significant end of the word: + +* Destination (server number), 32 bits + This specifies where the interrupt should be sent, and is the + interrupt server number specified for the destination vcpu. + +* Priority, 8 bits + This is the priority specified for this interrupt source, where 0 is + the highest priority and 255 is the lowest. An interrupt with a + priority of 255 will never be delivered. + +* Level sensitive flag, 1 bit + This bit is 1 for a level-sensitive interrupt source, or 0 for + edge-sensitive (or MSI). + +* Masked flag, 1 bit + This bit is set to 1 if the interrupt is masked (cannot be delivered + regardless of its priority), for example by the ibm,int-off RTAS + call, or 0 if it is not masked. + +* Pending flag, 1 bit + This bit is 1 if the source has a pending interrupt, otherwise 0. + +Only one XICS instance may be created per VM. diff --git a/Documentation/virt/kvm/devices/xive.txt b/Documentation/virt/kvm/devices/xive.txt new file mode 100644 index 000000000000..9a24a4525253 --- /dev/null +++ b/Documentation/virt/kvm/devices/xive.txt @@ -0,0 +1,197 @@ +POWER9 eXternal Interrupt Virtualization Engine (XIVE Gen1) +========================================================== + +Device types supported: + KVM_DEV_TYPE_XIVE POWER9 XIVE Interrupt Controller generation 1 + +This device acts as a VM interrupt controller. It provides the KVM +interface to configure the interrupt sources of a VM in the underlying +POWER9 XIVE interrupt controller. + +Only one XIVE instance may be instantiated. A guest XIVE device +requires a POWER9 host and the guest OS should have support for the +XIVE native exploitation interrupt mode. If not, it should run using +the legacy interrupt mode, referred as XICS (POWER7/8). + +* Device Mappings + + The KVM device exposes different MMIO ranges of the XIVE HW which + are required for interrupt management. These are exposed to the + guest in VMAs populated with a custom VM fault handler. + + 1. Thread Interrupt Management Area (TIMA) + + Each thread has an associated Thread Interrupt Management context + composed of a set of registers. These registers let the thread + handle priority management and interrupt acknowledgment. The most + important are : + + - Interrupt Pending Buffer (IPB) + - Current Processor Priority (CPPR) + - Notification Source Register (NSR) + + They are exposed to software in four different pages each proposing + a view with a different privilege. The first page is for the + physical thread context and the second for the hypervisor. Only the + third (operating system) and the fourth (user level) are exposed the + guest. + + 2. Event State Buffer (ESB) + + Each source is associated with an Event State Buffer (ESB) with + either a pair of even/odd pair of pages which provides commands to + manage the source: to trigger, to EOI, to turn off the source for + instance. + + 3. Device pass-through + + When a device is passed-through into the guest, the source + interrupts are from a different HW controller (PHB4) and the ESB + pages exposed to the guest should accommadate this change. + + The passthru_irq helpers, kvmppc_xive_set_mapped() and + kvmppc_xive_clr_mapped() are called when the device HW irqs are + mapped into or unmapped from the guest IRQ number space. The KVM + device extends these helpers to clear the ESB pages of the guest IRQ + number being mapped and then lets the VM fault handler repopulate. + The handler will insert the ESB page corresponding to the HW + interrupt of the device being passed-through or the initial IPI ESB + page if the device has being removed. + + The ESB remapping is fully transparent to the guest and the OS + device driver. All handling is done within VFIO and the above + helpers in KVM-PPC. + +* Groups: + + 1. KVM_DEV_XIVE_GRP_CTRL + Provides global controls on the device + Attributes: + 1.1 KVM_DEV_XIVE_RESET (write only) + Resets the interrupt controller configuration for sources and event + queues. To be used by kexec and kdump. + Errors: none + + 1.2 KVM_DEV_XIVE_EQ_SYNC (write only) + Sync all the sources and queues and mark the EQ pages dirty. This + to make sure that a consistent memory state is captured when + migrating the VM. + Errors: none + + 2. KVM_DEV_XIVE_GRP_SOURCE (write only) + Initializes a new source in the XIVE device and mask it. + Attributes: + Interrupt source number (64-bit) + The kvm_device_attr.addr points to a __u64 value: + bits: | 63 .... 2 | 1 | 0 + values: | unused | level | type + - type: 0:MSI 1:LSI + - level: assertion level in case of an LSI. + Errors: + -E2BIG: Interrupt source number is out of range + -ENOMEM: Could not create a new source block + -EFAULT: Invalid user pointer for attr->addr. + -ENXIO: Could not allocate underlying HW interrupt + + 3. KVM_DEV_XIVE_GRP_SOURCE_CONFIG (write only) + Configures source targeting + Attributes: + Interrupt source number (64-bit) + The kvm_device_attr.addr points to a __u64 value: + bits: | 63 .... 33 | 32 | 31 .. 3 | 2 .. 0 + values: | eisn | mask | server | priority + - priority: 0-7 interrupt priority level + - server: CPU number chosen to handle the interrupt + - mask: mask flag (unused) + - eisn: Effective Interrupt Source Number + Errors: + -ENOENT: Unknown source number + -EINVAL: Not initialized source number + -EINVAL: Invalid priority + -EINVAL: Invalid CPU number. + -EFAULT: Invalid user pointer for attr->addr. + -ENXIO: CPU event queues not configured or configuration of the + underlying HW interrupt failed + -EBUSY: No CPU available to serve interrupt + + 4. KVM_DEV_XIVE_GRP_EQ_CONFIG (read-write) + Configures an event queue of a CPU + Attributes: + EQ descriptor identifier (64-bit) + The EQ descriptor identifier is a tuple (server, priority) : + bits: | 63 .... 32 | 31 .. 3 | 2 .. 0 + values: | unused | server | priority + The kvm_device_attr.addr points to : + struct kvm_ppc_xive_eq { + __u32 flags; + __u32 qshift; + __u64 qaddr; + __u32 qtoggle; + __u32 qindex; + __u8 pad[40]; + }; + - flags: queue flags + KVM_XIVE_EQ_ALWAYS_NOTIFY (required) + forces notification without using the coalescing mechanism + provided by the XIVE END ESBs. + - qshift: queue size (power of 2) + - qaddr: real address of queue + - qtoggle: current queue toggle bit + - qindex: current queue index + - pad: reserved for future use + Errors: + -ENOENT: Invalid CPU number + -EINVAL: Invalid priority + -EINVAL: Invalid flags + -EINVAL: Invalid queue size + -EINVAL: Invalid queue address + -EFAULT: Invalid user pointer for attr->addr. + -EIO: Configuration of the underlying HW failed + + 5. KVM_DEV_XIVE_GRP_SOURCE_SYNC (write only) + Synchronize the source to flush event notifications + Attributes: + Interrupt source number (64-bit) + Errors: + -ENOENT: Unknown source number + -EINVAL: Not initialized source number + +* VCPU state + + The XIVE IC maintains VP interrupt state in an internal structure + called the NVT. When a VP is not dispatched on a HW processor + thread, this structure can be updated by HW if the VP is the target + of an event notification. + + It is important for migration to capture the cached IPB from the NVT + as it synthesizes the priorities of the pending interrupts. We + capture a bit more to report debug information. + + KVM_REG_PPC_VP_STATE (2 * 64bits) + bits: | 63 .... 32 | 31 .... 0 | + values: | TIMA word0 | TIMA word1 | + bits: | 127 .......... 64 | + values: | unused | + +* Migration: + + Saving the state of a VM using the XIVE native exploitation mode + should follow a specific sequence. When the VM is stopped : + + 1. Mask all sources (PQ=01) to stop the flow of events. + + 2. Sync the XIVE device with the KVM control KVM_DEV_XIVE_EQ_SYNC to + flush any in-flight event notification and to stabilize the EQs. At + this stage, the EQ pages are marked dirty to make sure they are + transferred in the migration sequence. + + 3. Capture the state of the source targeting, the EQs configuration + and the state of thread interrupt context registers. + + Restore is similar : + + 1. Restore the EQ configuration. As targeting depends on it. + 2. Restore targeting + 3. Restore the thread interrupt contexts + 4. Restore the source states + 5. Let the vCPU run diff --git a/Documentation/virt/kvm/halt-polling.txt b/Documentation/virt/kvm/halt-polling.txt new file mode 100644 index 000000000000..4f791b128dd2 --- /dev/null +++ b/Documentation/virt/kvm/halt-polling.txt @@ -0,0 +1,136 @@ +The KVM halt polling system +=========================== + +The KVM halt polling system provides a feature within KVM whereby the latency +of a guest can, under some circumstances, be reduced by polling in the host +for some time period after the guest has elected to no longer run by cedeing. +That is, when a guest vcpu has ceded, or in the case of powerpc when all of the +vcpus of a single vcore have ceded, the host kernel polls for wakeup conditions +before giving up the cpu to the scheduler in order to let something else run. + +Polling provides a latency advantage in cases where the guest can be run again +very quickly by at least saving us a trip through the scheduler, normally on +the order of a few micro-seconds, although performance benefits are workload +dependant. In the event that no wakeup source arrives during the polling +interval or some other task on the runqueue is runnable the scheduler is +invoked. Thus halt polling is especially useful on workloads with very short +wakeup periods where the time spent halt polling is minimised and the time +savings of not invoking the scheduler are distinguishable. + +The generic halt polling code is implemented in: + + virt/kvm/kvm_main.c: kvm_vcpu_block() + +The powerpc kvm-hv specific case is implemented in: + + arch/powerpc/kvm/book3s_hv.c: kvmppc_vcore_blocked() + +Halt Polling Interval +===================== + +The maximum time for which to poll before invoking the scheduler, referred to +as the halt polling interval, is increased and decreased based on the perceived +effectiveness of the polling in an attempt to limit pointless polling. +This value is stored in either the vcpu struct: + + kvm_vcpu->halt_poll_ns + +or in the case of powerpc kvm-hv, in the vcore struct: + + kvmppc_vcore->halt_poll_ns + +Thus this is a per vcpu (or vcore) value. + +During polling if a wakeup source is received within the halt polling interval, +the interval is left unchanged. In the event that a wakeup source isn't +received during the polling interval (and thus schedule is invoked) there are +two options, either the polling interval and total block time[0] were less than +the global max polling interval (see module params below), or the total block +time was greater than the global max polling interval. + +In the event that both the polling interval and total block time were less than +the global max polling interval then the polling interval can be increased in +the hope that next time during the longer polling interval the wake up source +will be received while the host is polling and the latency benefits will be +received. The polling interval is grown in the function grow_halt_poll_ns() and +is multiplied by the module parameters halt_poll_ns_grow and +halt_poll_ns_grow_start. + +In the event that the total block time was greater than the global max polling +interval then the host will never poll for long enough (limited by the global +max) to wakeup during the polling interval so it may as well be shrunk in order +to avoid pointless polling. The polling interval is shrunk in the function +shrink_halt_poll_ns() and is divided by the module parameter +halt_poll_ns_shrink, or set to 0 iff halt_poll_ns_shrink == 0. + +It is worth noting that this adjustment process attempts to hone in on some +steady state polling interval but will only really do a good job for wakeups +which come at an approximately constant rate, otherwise there will be constant +adjustment of the polling interval. + +[0] total block time: the time between when the halt polling function is + invoked and a wakeup source received (irrespective of + whether the scheduler is invoked within that function). + +Module Parameters +================= + +The kvm module has 3 tuneable module parameters to adjust the global max +polling interval as well as the rate at which the polling interval is grown and +shrunk. These variables are defined in include/linux/kvm_host.h and as module +parameters in virt/kvm/kvm_main.c, or arch/powerpc/kvm/book3s_hv.c in the +powerpc kvm-hv case. + +Module Parameter | Description | Default Value +-------------------------------------------------------------------------------- +halt_poll_ns | The global max polling | KVM_HALT_POLL_NS_DEFAULT + | interval which defines | + | the ceiling value of the | + | polling interval for | (per arch value) + | each vcpu. | +-------------------------------------------------------------------------------- +halt_poll_ns_grow | The value by which the | 2 + | halt polling interval is | + | multiplied in the | + | grow_halt_poll_ns() | + | function. | +-------------------------------------------------------------------------------- +halt_poll_ns_grow_start | The initial value to grow | 10000 + | to from zero in the | + | grow_halt_poll_ns() | + | function. | +-------------------------------------------------------------------------------- +halt_poll_ns_shrink | The value by which the | 0 + | halt polling interval is | + | divided in the | + | shrink_halt_poll_ns() | + | function. | +-------------------------------------------------------------------------------- + +These module parameters can be set from the debugfs files in: + + /sys/module/kvm/parameters/ + +Note: that these module parameters are system wide values and are not able to + be tuned on a per vm basis. + +Further Notes +============= + +- Care should be taken when setting the halt_poll_ns module parameter as a +large value has the potential to drive the cpu usage to 100% on a machine which +would be almost entirely idle otherwise. This is because even if a guest has +wakeups during which very little work is done and which are quite far apart, if +the period is shorter than the global max polling interval (halt_poll_ns) then +the host will always poll for the entire block time and thus cpu utilisation +will go to 100%. + +- Halt polling essentially presents a trade off between power usage and latency +and the module parameters should be used to tune the affinity for this. Idle +cpu time is essentially converted to host kernel time with the aim of decreasing +latency when entering the guest. + +- Halt polling will only be conducted by the host when no other tasks are +runnable on that cpu, otherwise the polling will cease immediately and +schedule will be invoked to allow that other task to run. Thus this doesn't +allow a guest to denial of service the cpu. diff --git a/Documentation/virt/kvm/hypercalls.txt b/Documentation/virt/kvm/hypercalls.txt new file mode 100644 index 000000000000..5f6d291bd004 --- /dev/null +++ b/Documentation/virt/kvm/hypercalls.txt @@ -0,0 +1,154 @@ +Linux KVM Hypercall: +=================== +X86: + KVM Hypercalls have a three-byte sequence of either the vmcall or the vmmcall + instruction. The hypervisor can replace it with instructions that are + guaranteed to be supported. + + Up to four arguments may be passed in rbx, rcx, rdx, and rsi respectively. + The hypercall number should be placed in rax and the return value will be + placed in rax. No other registers will be clobbered unless explicitly stated + by the particular hypercall. + +S390: + R2-R7 are used for parameters 1-6. In addition, R1 is used for hypercall + number. The return value is written to R2. + + S390 uses diagnose instruction as hypercall (0x500) along with hypercall + number in R1. + + For further information on the S390 diagnose call as supported by KVM, + refer to Documentation/virt/kvm/s390-diag.txt. + + PowerPC: + It uses R3-R10 and hypercall number in R11. R4-R11 are used as output registers. + Return value is placed in R3. + + KVM hypercalls uses 4 byte opcode, that are patched with 'hypercall-instructions' + property inside the device tree's /hypervisor node. + For more information refer to Documentation/virt/kvm/ppc-pv.txt + +MIPS: + KVM hypercalls use the HYPCALL instruction with code 0 and the hypercall + number in $2 (v0). Up to four arguments may be placed in $4-$7 (a0-a3) and + the return value is placed in $2 (v0). + +KVM Hypercalls Documentation +=========================== +The template for each hypercall is: +1. Hypercall name. +2. Architecture(s) +3. Status (deprecated, obsolete, active) +4. Purpose + +1. KVM_HC_VAPIC_POLL_IRQ +------------------------ +Architecture: x86 +Status: active +Purpose: Trigger guest exit so that the host can check for pending +interrupts on reentry. + +2. KVM_HC_MMU_OP +------------------------ +Architecture: x86 +Status: deprecated. +Purpose: Support MMU operations such as writing to PTE, +flushing TLB, release PT. + +3. KVM_HC_FEATURES +------------------------ +Architecture: PPC +Status: active +Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid +used to enumerate which hypercalls are available. On PPC, either device tree +based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration +mechanism (which is this hypercall) can be used. + +4. KVM_HC_PPC_MAP_MAGIC_PAGE +------------------------ +Architecture: PPC +Status: active +Purpose: To enable communication between the hypervisor and guest there is a +shared page that contains parts of supervisor visible register state. +The guest can map this shared page to access its supervisor register through +memory using this hypercall. + +5. KVM_HC_KICK_CPU +------------------------ +Architecture: x86 +Status: active +Purpose: Hypercall used to wakeup a vcpu from HLT state +Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest +kernel mode for an event to occur (ex: a spinlock to become available) can +execute HLT instruction once it has busy-waited for more than a threshold +time-interval. Execution of HLT instruction would cause the hypervisor to put +the vcpu to sleep until occurrence of an appropriate event. Another vcpu of the +same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall, +specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0) +is used in the hypercall for future use. + + +6. KVM_HC_CLOCK_PAIRING +------------------------ +Architecture: x86 +Status: active +Purpose: Hypercall used to synchronize host and guest clocks. +Usage: + +a0: guest physical address where host copies +"struct kvm_clock_offset" structure. + +a1: clock_type, ATM only KVM_CLOCK_PAIRING_WALLCLOCK (0) +is supported (corresponding to the host's CLOCK_REALTIME clock). + + struct kvm_clock_pairing { + __s64 sec; + __s64 nsec; + __u64 tsc; + __u32 flags; + __u32 pad[9]; + }; + + Where: + * sec: seconds from clock_type clock. + * nsec: nanoseconds from clock_type clock. + * tsc: guest TSC value used to calculate sec/nsec pair + * flags: flags, unused (0) at the moment. + +The hypercall lets a guest compute a precise timestamp across +host and guest. The guest can use the returned TSC value to +compute the CLOCK_REALTIME for its clock, at the same instant. + +Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource, +or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK. + +6. KVM_HC_SEND_IPI +------------------------ +Architecture: x86 +Status: active +Purpose: Send IPIs to multiple vCPUs. + +a0: lower part of the bitmap of destination APIC IDs +a1: higher part of the bitmap of destination APIC IDs +a2: the lowest APIC ID in bitmap +a3: APIC ICR + +The hypercall lets a guest send multicast IPIs, with at most 128 +128 destinations per hypercall in 64-bit mode and 64 vCPUs per +hypercall in 32-bit mode. The destinations are represented by a +bitmap contained in the first two arguments (a0 and a1). Bit 0 of +a0 corresponds to the APIC ID in the third argument (a2), bit 1 +corresponds to the APIC ID a2+1, and so on. + +Returns the number of CPUs to which the IPIs were delivered successfully. + +7. KVM_HC_SCHED_YIELD +------------------------ +Architecture: x86 +Status: active +Purpose: Hypercall used to yield if the IPI target vCPU is preempted + +a0: destination APIC ID + +Usage example: When sending a call-function IPI-many to vCPUs, yield if +any of the IPI target vCPUs was preempted. diff --git a/Documentation/virt/kvm/index.rst b/Documentation/virt/kvm/index.rst new file mode 100644 index 000000000000..ada224a511fe --- /dev/null +++ b/Documentation/virt/kvm/index.rst @@ -0,0 +1,12 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=== +KVM +=== + +.. toctree:: + :maxdepth: 2 + + amd-memory-encryption + cpuid + vcpu-requests diff --git a/Documentation/virt/kvm/locking.txt b/Documentation/virt/kvm/locking.txt new file mode 100644 index 000000000000..635cd6eaf714 --- /dev/null +++ b/Documentation/virt/kvm/locking.txt @@ -0,0 +1,215 @@ +KVM Lock Overview +================= + +1. Acquisition Orders +--------------------- + +The acquisition orders for mutexes are as follows: + +- kvm->lock is taken outside vcpu->mutex + +- kvm->lock is taken outside kvm->slots_lock and kvm->irq_lock + +- kvm->slots_lock is taken outside kvm->irq_lock, though acquiring + them together is quite rare. + +On x86, vcpu->mutex is taken outside kvm->arch.hyperv.hv_lock. + +Everything else is a leaf: no other lock is taken inside the critical +sections. + +2: Exception +------------ + +Fast page fault: + +Fast page fault is the fast path which fixes the guest page fault out of +the mmu-lock on x86. Currently, the page fault can be fast in one of the +following two cases: + +1. Access Tracking: The SPTE is not present, but it is marked for access +tracking i.e. the SPTE_SPECIAL_MASK is set. That means we need to +restore the saved R/X bits. This is described in more detail later below. + +2. Write-Protection: The SPTE is present and the fault is +caused by write-protect. That means we just need to change the W bit of the +spte. + +What we use to avoid all the race is the SPTE_HOST_WRITEABLE bit and +SPTE_MMU_WRITEABLE bit on the spte: +- SPTE_HOST_WRITEABLE means the gfn is writable on host. +- SPTE_MMU_WRITEABLE means the gfn is writable on mmu. The bit is set when + the gfn is writable on guest mmu and it is not write-protected by shadow + page write-protection. + +On fast page fault path, we will use cmpxchg to atomically set the spte W +bit if spte.SPTE_HOST_WRITEABLE = 1 and spte.SPTE_WRITE_PROTECT = 1, or +restore the saved R/X bits if VMX_EPT_TRACK_ACCESS mask is set, or both. This +is safe because whenever changing these bits can be detected by cmpxchg. + +But we need carefully check these cases: +1): The mapping from gfn to pfn +The mapping from gfn to pfn may be changed since we can only ensure the pfn +is not changed during cmpxchg. This is a ABA problem, for example, below case +will happen: + +At the beginning: +gpte = gfn1 +gfn1 is mapped to pfn1 on host +spte is the shadow page table entry corresponding with gpte and +spte = pfn1 + + VCPU 0 VCPU0 +on fast page fault path: + + old_spte = *spte; + pfn1 is swapped out: + spte = 0; + + pfn1 is re-alloced for gfn2. + + gpte is changed to point to + gfn2 by the guest: + spte = pfn1; + + if (cmpxchg(spte, old_spte, old_spte+W) + mark_page_dirty(vcpu->kvm, gfn1) + OOPS!!! + +We dirty-log for gfn1, that means gfn2 is lost in dirty-bitmap. + +For direct sp, we can easily avoid it since the spte of direct sp is fixed +to gfn. For indirect sp, before we do cmpxchg, we call gfn_to_pfn_atomic() +to pin gfn to pfn, because after gfn_to_pfn_atomic(): +- We have held the refcount of pfn that means the pfn can not be freed and + be reused for another gfn. +- The pfn is writable that means it can not be shared between different gfns + by KSM. + +Then, we can ensure the dirty bitmaps is correctly set for a gfn. + +Currently, to simplify the whole things, we disable fast page fault for +indirect shadow page. + +2): Dirty bit tracking +In the origin code, the spte can be fast updated (non-atomically) if the +spte is read-only and the Accessed bit has already been set since the +Accessed bit and Dirty bit can not be lost. + +But it is not true after fast page fault since the spte can be marked +writable between reading spte and updating spte. Like below case: + +At the beginning: +spte.W = 0 +spte.Accessed = 1 + + VCPU 0 VCPU0 +In mmu_spte_clear_track_bits(): + + old_spte = *spte; + + /* 'if' condition is satisfied. */ + if (old_spte.Accessed == 1 && + old_spte.W == 0) + spte = 0ull; + on fast page fault path: + spte.W = 1 + memory write on the spte: + spte.Dirty = 1 + + + else + old_spte = xchg(spte, 0ull) + + + if (old_spte.Accessed == 1) + kvm_set_pfn_accessed(spte.pfn); + if (old_spte.Dirty == 1) + kvm_set_pfn_dirty(spte.pfn); + OOPS!!! + +The Dirty bit is lost in this case. + +In order to avoid this kind of issue, we always treat the spte as "volatile" +if it can be updated out of mmu-lock, see spte_has_volatile_bits(), it means, +the spte is always atomically updated in this case. + +3): flush tlbs due to spte updated +If the spte is updated from writable to readonly, we should flush all TLBs, +otherwise rmap_write_protect will find a read-only spte, even though the +writable spte might be cached on a CPU's TLB. + +As mentioned before, the spte can be updated to writable out of mmu-lock on +fast page fault path, in order to easily audit the path, we see if TLBs need +be flushed caused by this reason in mmu_spte_update() since this is a common +function to update spte (present -> present). + +Since the spte is "volatile" if it can be updated out of mmu-lock, we always +atomically update the spte, the race caused by fast page fault can be avoided, +See the comments in spte_has_volatile_bits() and mmu_spte_update(). + +Lockless Access Tracking: + +This is used for Intel CPUs that are using EPT but do not support the EPT A/D +bits. In this case, when the KVM MMU notifier is called to track accesses to a +page (via kvm_mmu_notifier_clear_flush_young), it marks the PTE as not-present +by clearing the RWX bits in the PTE and storing the original R & X bits in +some unused/ignored bits. In addition, the SPTE_SPECIAL_MASK is also set on the +PTE (using the ignored bit 62). When the VM tries to access the page later on, +a fault is generated and the fast page fault mechanism described above is used +to atomically restore the PTE to a Present state. The W bit is not saved when +the PTE is marked for access tracking and during restoration to the Present +state, the W bit is set depending on whether or not it was a write access. If +it wasn't, then the W bit will remain clear until a write access happens, at +which time it will be set using the Dirty tracking mechanism described above. + +3. Reference +------------ + +Name: kvm_lock +Type: mutex +Arch: any +Protects: - vm_list + +Name: kvm_count_lock +Type: raw_spinlock_t +Arch: any +Protects: - hardware virtualization enable/disable +Comment: 'raw' because hardware enabling/disabling must be atomic /wrt + migration. + +Name: kvm_arch::tsc_write_lock +Type: raw_spinlock +Arch: x86 +Protects: - kvm_arch::{last_tsc_write,last_tsc_nsec,last_tsc_offset} + - tsc offset in vmcb +Comment: 'raw' because updating the tsc offsets must not be preempted. + +Name: kvm->mmu_lock +Type: spinlock_t +Arch: any +Protects: -shadow page/shadow tlb entry +Comment: it is a spinlock since it is used in mmu notifier. + +Name: kvm->srcu +Type: srcu lock +Arch: any +Protects: - kvm->memslots + - kvm->buses +Comment: The srcu read lock must be held while accessing memslots (e.g. + when using gfn_to_* functions) and while accessing in-kernel + MMIO/PIO address->device structure mapping (kvm->buses). + The srcu index can be stored in kvm_vcpu->srcu_idx per vcpu + if it is needed by multiple functions. + +Name: blocked_vcpu_on_cpu_lock +Type: spinlock_t +Arch: x86 +Protects: blocked_vcpu_on_cpu +Comment: This is a per-CPU lock and it is used for VT-d posted-interrupts. + When VT-d posted-interrupts is supported and the VM has assigned + devices, we put the blocked vCPU on the list blocked_vcpu_on_cpu + protected by blocked_vcpu_on_cpu_lock, when VT-d hardware issues + wakeup notification event since external interrupts from the + assigned devices happens, we will find the vCPU on the list to + wakeup. diff --git a/Documentation/virt/kvm/mmu.txt b/Documentation/virt/kvm/mmu.txt new file mode 100644 index 000000000000..1b9880dfba0a --- /dev/null +++ b/Documentation/virt/kvm/mmu.txt @@ -0,0 +1,449 @@ +The x86 kvm shadow mmu +====================== + +The mmu (in arch/x86/kvm, files mmu.[ch] and paging_tmpl.h) is responsible +for presenting a standard x86 mmu to the guest, while translating guest +physical addresses to host physical addresses. + +The mmu code attempts to satisfy the following requirements: + +- correctness: the guest should not be able to determine that it is running + on an emulated mmu except for timing (we attempt to comply + with the specification, not emulate the characteristics of + a particular implementation such as tlb size) +- security: the guest must not be able to touch host memory not assigned + to it +- performance: minimize the performance penalty imposed by the mmu +- scaling: need to scale to large memory and large vcpu guests +- hardware: support the full range of x86 virtualization hardware +- integration: Linux memory management code must be in control of guest memory + so that swapping, page migration, page merging, transparent + hugepages, and similar features work without change +- dirty tracking: report writes to guest memory to enable live migration + and framebuffer-based displays +- footprint: keep the amount of pinned kernel memory low (most memory + should be shrinkable) +- reliability: avoid multipage or GFP_ATOMIC allocations + +Acronyms +======== + +pfn host page frame number +hpa host physical address +hva host virtual address +gfn guest frame number +gpa guest physical address +gva guest virtual address +ngpa nested guest physical address +ngva nested guest virtual address +pte page table entry (used also to refer generically to paging structure + entries) +gpte guest pte (referring to gfns) +spte shadow pte (referring to pfns) +tdp two dimensional paging (vendor neutral term for NPT and EPT) + +Virtual and real hardware supported +=================================== + +The mmu supports first-generation mmu hardware, which allows an atomic switch +of the current paging mode and cr3 during guest entry, as well as +two-dimensional paging (AMD's NPT and Intel's EPT). The emulated hardware +it exposes is the traditional 2/3/4 level x86 mmu, with support for global +pages, pae, pse, pse36, cr0.wp, and 1GB pages. Emulated hardware also +able to expose NPT capable hardware on NPT capable hosts. + +Translation +=========== + +The primary job of the mmu is to program the processor's mmu to translate +addresses for the guest. Different translations are required at different +times: + +- when guest paging is disabled, we translate guest physical addresses to + host physical addresses (gpa->hpa) +- when guest paging is enabled, we translate guest virtual addresses, to + guest physical addresses, to host physical addresses (gva->gpa->hpa) +- when the guest launches a guest of its own, we translate nested guest + virtual addresses, to nested guest physical addresses, to guest physical + addresses, to host physical addresses (ngva->ngpa->gpa->hpa) + +The primary challenge is to encode between 1 and 3 translations into hardware +that support only 1 (traditional) and 2 (tdp) translations. When the +number of required translations matches the hardware, the mmu operates in +direct mode; otherwise it operates in shadow mode (see below). + +Memory +====== + +Guest memory (gpa) is part of the user address space of the process that is +using kvm. Userspace defines the translation between guest addresses and user +addresses (gpa->hva); note that two gpas may alias to the same hva, but not +vice versa. + +These hvas may be backed using any method available to the host: anonymous +memory, file backed memory, and device memory. Memory might be paged by the +host at any time. + +Events +====== + +The mmu is driven by events, some from the guest, some from the host. + +Guest generated events: +- writes to control registers (especially cr3) +- invlpg/invlpga instruction execution +- access to missing or protected translations + +Host generated events: +- changes in the gpa->hpa translation (either through gpa->hva changes or + through hva->hpa changes) +- memory pressure (the shrinker) + +Shadow pages +============ + +The principal data structure is the shadow page, 'struct kvm_mmu_page'. A +shadow page contains 512 sptes, which can be either leaf or nonleaf sptes. A +shadow page may contain a mix of leaf and nonleaf sptes. + +A nonleaf spte allows the hardware mmu to reach the leaf pages and +is not related to a translation directly. It points to other shadow pages. + +A leaf spte corresponds to either one or two translations encoded into +one paging structure entry. These are always the lowest level of the +translation stack, with optional higher level translations left to NPT/EPT. +Leaf ptes point at guest pages. + +The following table shows translations encoded by leaf ptes, with higher-level +translations in parentheses: + + Non-nested guests: + nonpaging: gpa->hpa + paging: gva->gpa->hpa + paging, tdp: (gva->)gpa->hpa + Nested guests: + non-tdp: ngva->gpa->hpa (*) + tdp: (ngva->)ngpa->gpa->hpa + +(*) the guest hypervisor will encode the ngva->gpa translation into its page + tables if npt is not present + +Shadow pages contain the following information: + role.level: + The level in the shadow paging hierarchy that this shadow page belongs to. + 1=4k sptes, 2=2M sptes, 3=1G sptes, etc. + role.direct: + If set, leaf sptes reachable from this page are for a linear range. + Examples include real mode translation, large guest pages backed by small + host pages, and gpa->hpa translations when NPT or EPT is active. + The linear range starts at (gfn << PAGE_SHIFT) and its size is determined + by role.level (2MB for first level, 1GB for second level, 0.5TB for third + level, 256TB for fourth level) + If clear, this page corresponds to a guest page table denoted by the gfn + field. + role.quadrant: + When role.gpte_is_8_bytes=0, the guest uses 32-bit gptes while the host uses 64-bit + sptes. That means a guest page table contains more ptes than the host, + so multiple shadow pages are needed to shadow one guest page. + For first-level shadow pages, role.quadrant can be 0 or 1 and denotes the + first or second 512-gpte block in the guest page table. For second-level + page tables, each 32-bit gpte is converted to two 64-bit sptes + (since each first-level guest page is shadowed by two first-level + shadow pages) so role.quadrant takes values in the range 0..3. Each + quadrant maps 1GB virtual address space. + role.access: + Inherited guest access permissions in the form uwx. Note execute + permission is positive, not negative. + role.invalid: + The page is invalid and should not be used. It is a root page that is + currently pinned (by a cpu hardware register pointing to it); once it is + unpinned it will be destroyed. + role.gpte_is_8_bytes: + Reflects the size of the guest PTE for which the page is valid, i.e. '1' + if 64-bit gptes are in use, '0' if 32-bit gptes are in use. + role.nxe: + Contains the value of efer.nxe for which the page is valid. + role.cr0_wp: + Contains the value of cr0.wp for which the page is valid. + role.smep_andnot_wp: + Contains the value of cr4.smep && !cr0.wp for which the page is valid + (pages for which this is true are different from other pages; see the + treatment of cr0.wp=0 below). + role.smap_andnot_wp: + Contains the value of cr4.smap && !cr0.wp for which the page is valid + (pages for which this is true are different from other pages; see the + treatment of cr0.wp=0 below). + role.ept_sp: + This is a virtual flag to denote a shadowed nested EPT page. ept_sp + is true if "cr0_wp && smap_andnot_wp", an otherwise invalid combination. + role.smm: + Is 1 if the page is valid in system management mode. This field + determines which of the kvm_memslots array was used to build this + shadow page; it is also used to go back from a struct kvm_mmu_page + to a memslot, through the kvm_memslots_for_spte_role macro and + __gfn_to_memslot. + role.ad_disabled: + Is 1 if the MMU instance cannot use A/D bits. EPT did not have A/D + bits before Haswell; shadow EPT page tables also cannot use A/D bits + if the L1 hypervisor does not enable them. + gfn: + Either the guest page table containing the translations shadowed by this + page, or the base page frame for linear translations. See role.direct. + spt: + A pageful of 64-bit sptes containing the translations for this page. + Accessed by both kvm and hardware. + The page pointed to by spt will have its page->private pointing back + at the shadow page structure. + sptes in spt point either at guest pages, or at lower-level shadow pages. + Specifically, if sp1 and sp2 are shadow pages, then sp1->spt[n] may point + at __pa(sp2->spt). sp2 will point back at sp1 through parent_pte. + The spt array forms a DAG structure with the shadow page as a node, and + guest pages as leaves. + gfns: + An array of 512 guest frame numbers, one for each present pte. Used to + perform a reverse map from a pte to a gfn. When role.direct is set, any + element of this array can be calculated from the gfn field when used, in + this case, the array of gfns is not allocated. See role.direct and gfn. + root_count: + A counter keeping track of how many hardware registers (guest cr3 or + pdptrs) are now pointing at the page. While this counter is nonzero, the + page cannot be destroyed. See role.invalid. + parent_ptes: + The reverse mapping for the pte/ptes pointing at this page's spt. If + parent_ptes bit 0 is zero, only one spte points at this page and + parent_ptes points at this single spte, otherwise, there exists multiple + sptes pointing at this page and (parent_ptes & ~0x1) points at a data + structure with a list of parent sptes. + unsync: + If true, then the translations in this page may not match the guest's + translation. This is equivalent to the state of the tlb when a pte is + changed but before the tlb entry is flushed. Accordingly, unsync ptes + are synchronized when the guest executes invlpg or flushes its tlb by + other means. Valid for leaf pages. + unsync_children: + How many sptes in the page point at pages that are unsync (or have + unsynchronized children). + unsync_child_bitmap: + A bitmap indicating which sptes in spt point (directly or indirectly) at + pages that may be unsynchronized. Used to quickly locate all unsychronized + pages reachable from a given page. + clear_spte_count: + Only present on 32-bit hosts, where a 64-bit spte cannot be written + atomically. The reader uses this while running out of the MMU lock + to detect in-progress updates and retry them until the writer has + finished the write. + write_flooding_count: + A guest may write to a page table many times, causing a lot of + emulations if the page needs to be write-protected (see "Synchronized + and unsynchronized pages" below). Leaf pages can be unsynchronized + so that they do not trigger frequent emulation, but this is not + possible for non-leafs. This field counts the number of emulations + since the last time the page table was actually used; if emulation + is triggered too frequently on this page, KVM will unmap the page + to avoid emulation in the future. + +Reverse map +=========== + +The mmu maintains a reverse mapping whereby all ptes mapping a page can be +reached given its gfn. This is used, for example, when swapping out a page. + +Synchronized and unsynchronized pages +===================================== + +The guest uses two events to synchronize its tlb and page tables: tlb flushes +and page invalidations (invlpg). + +A tlb flush means that we need to synchronize all sptes reachable from the +guest's cr3. This is expensive, so we keep all guest page tables write +protected, and synchronize sptes to gptes when a gpte is written. + +A special case is when a guest page table is reachable from the current +guest cr3. In this case, the guest is obliged to issue an invlpg instruction +before using the translation. We take advantage of that by removing write +protection from the guest page, and allowing the guest to modify it freely. +We synchronize modified gptes when the guest invokes invlpg. This reduces +the amount of emulation we have to do when the guest modifies multiple gptes, +or when the a guest page is no longer used as a page table and is used for +random guest data. + +As a side effect we have to resynchronize all reachable unsynchronized shadow +pages on a tlb flush. + + +Reaction to events +================== + +- guest page fault (or npt page fault, or ept violation) + +This is the most complicated event. The cause of a page fault can be: + + - a true guest fault (the guest translation won't allow the access) (*) + - access to a missing translation + - access to a protected translation + - when logging dirty pages, memory is write protected + - synchronized shadow pages are write protected (*) + - access to untranslatable memory (mmio) + + (*) not applicable in direct mode + +Handling a page fault is performed as follows: + + - if the RSV bit of the error code is set, the page fault is caused by guest + accessing MMIO and cached MMIO information is available. + - walk shadow page table + - check for valid generation number in the spte (see "Fast invalidation of + MMIO sptes" below) + - cache the information to vcpu->arch.mmio_gva, vcpu->arch.access and + vcpu->arch.mmio_gfn, and call the emulator + - If both P bit and R/W bit of error code are set, this could possibly + be handled as a "fast page fault" (fixed without taking the MMU lock). See + the description in Documentation/virt/kvm/locking.txt. + - if needed, walk the guest page tables to determine the guest translation + (gva->gpa or ngpa->gpa) + - if permissions are insufficient, reflect the fault back to the guest + - determine the host page + - if this is an mmio request, there is no host page; cache the info to + vcpu->arch.mmio_gva, vcpu->arch.access and vcpu->arch.mmio_gfn + - walk the shadow page table to find the spte for the translation, + instantiating missing intermediate page tables as necessary + - If this is an mmio request, cache the mmio info to the spte and set some + reserved bit on the spte (see callers of kvm_mmu_set_mmio_spte_mask) + - try to unsynchronize the page + - if successful, we can let the guest continue and modify the gpte + - emulate the instruction + - if failed, unshadow the page and let the guest continue + - update any translations that were modified by the instruction + +invlpg handling: + + - walk the shadow page hierarchy and drop affected translations + - try to reinstantiate the indicated translation in the hope that the + guest will use it in the near future + +Guest control register updates: + +- mov to cr3 + - look up new shadow roots + - synchronize newly reachable shadow pages + +- mov to cr0/cr4/efer + - set up mmu context for new paging mode + - look up new shadow roots + - synchronize newly reachable shadow pages + +Host translation updates: + + - mmu notifier called with updated hva + - look up affected sptes through reverse map + - drop (or update) translations + +Emulating cr0.wp +================ + +If tdp is not enabled, the host must keep cr0.wp=1 so page write protection +works for the guest kernel, not guest guest userspace. When the guest +cr0.wp=1, this does not present a problem. However when the guest cr0.wp=0, +we cannot map the permissions for gpte.u=1, gpte.w=0 to any spte (the +semantics require allowing any guest kernel access plus user read access). + +We handle this by mapping the permissions to two possible sptes, depending +on fault type: + +- kernel write fault: spte.u=0, spte.w=1 (allows full kernel access, + disallows user access) +- read fault: spte.u=1, spte.w=0 (allows full read access, disallows kernel + write access) + +(user write faults generate a #PF) + +In the first case there are two additional complications: +- if CR4.SMEP is enabled: since we've turned the page into a kernel page, + the kernel may now execute it. We handle this by also setting spte.nx. + If we get a user fetch or read fault, we'll change spte.u=1 and + spte.nx=gpte.nx back. For this to work, KVM forces EFER.NX to 1 when + shadow paging is in use. +- if CR4.SMAP is disabled: since the page has been changed to a kernel + page, it can not be reused when CR4.SMAP is enabled. We set + CR4.SMAP && !CR0.WP into shadow page's role to avoid this case. Note, + here we do not care the case that CR4.SMAP is enabled since KVM will + directly inject #PF to guest due to failed permission check. + +To prevent an spte that was converted into a kernel page with cr0.wp=0 +from being written by the kernel after cr0.wp has changed to 1, we make +the value of cr0.wp part of the page role. This means that an spte created +with one value of cr0.wp cannot be used when cr0.wp has a different value - +it will simply be missed by the shadow page lookup code. A similar issue +exists when an spte created with cr0.wp=0 and cr4.smep=0 is used after +changing cr4.smep to 1. To avoid this, the value of !cr0.wp && cr4.smep +is also made a part of the page role. + +Large pages +=========== + +The mmu supports all combinations of large and small guest and host pages. +Supported page sizes include 4k, 2M, 4M, and 1G. 4M pages are treated as +two separate 2M pages, on both guest and host, since the mmu always uses PAE +paging. + +To instantiate a large spte, four constraints must be satisfied: + +- the spte must point to a large host page +- the guest pte must be a large pte of at least equivalent size (if tdp is + enabled, there is no guest pte and this condition is satisfied) +- if the spte will be writeable, the large page frame may not overlap any + write-protected pages +- the guest page must be wholly contained by a single memory slot + +To check the last two conditions, the mmu maintains a ->disallow_lpage set of +arrays for each memory slot and large page size. Every write protected page +causes its disallow_lpage to be incremented, thus preventing instantiation of +a large spte. The frames at the end of an unaligned memory slot have +artificially inflated ->disallow_lpages so they can never be instantiated. + +Fast invalidation of MMIO sptes +=============================== + +As mentioned in "Reaction to events" above, kvm will cache MMIO +information in leaf sptes. When a new memslot is added or an existing +memslot is changed, this information may become stale and needs to be +invalidated. This also needs to hold the MMU lock while walking all +shadow pages, and is made more scalable with a similar technique. + +MMIO sptes have a few spare bits, which are used to store a +generation number. The global generation number is stored in +kvm_memslots(kvm)->generation, and increased whenever guest memory info +changes. + +When KVM finds an MMIO spte, it checks the generation number of the spte. +If the generation number of the spte does not equal the global generation +number, it will ignore the cached MMIO information and handle the page +fault through the slow path. + +Since only 19 bits are used to store generation-number on mmio spte, all +pages are zapped when there is an overflow. + +Unfortunately, a single memory access might access kvm_memslots(kvm) multiple +times, the last one happening when the generation number is retrieved and +stored into the MMIO spte. Thus, the MMIO spte might be created based on +out-of-date information, but with an up-to-date generation number. + +To avoid this, the generation number is incremented again after synchronize_srcu +returns; thus, bit 63 of kvm_memslots(kvm)->generation set to 1 only during a +memslot update, while some SRCU readers might be using the old copy. We do not +want to use an MMIO sptes created with an odd generation number, and we can do +this without losing a bit in the MMIO spte. The "update in-progress" bit of the +generation is not stored in MMIO spte, and is so is implicitly zero when the +generation is extracted out of the spte. If KVM is unlucky and creates an MMIO +spte while an update is in-progress, the next access to the spte will always be +a cache miss. For example, a subsequent access during the update window will +miss due to the in-progress flag diverging, while an access after the update +window closes will have a higher generation number (as compared to the spte). + + +Further reading +=============== + +- NPT presentation from KVM Forum 2008 + http://www.linux-kvm.org/images/c/c8/KvmForum2008%24kdf2008_21.pdf + diff --git a/Documentation/virt/kvm/msr.txt b/Documentation/virt/kvm/msr.txt new file mode 100644 index 000000000000..df1f4338b3ca --- /dev/null +++ b/Documentation/virt/kvm/msr.txt @@ -0,0 +1,284 @@ +KVM-specific MSRs. +Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010 +===================================================== + +KVM makes use of some custom MSRs to service some requests. + +Custom MSRs have a range reserved for them, that goes from +0x4b564d00 to 0x4b564dff. There are MSRs outside this area, +but they are deprecated and their use is discouraged. + +Custom MSR list +-------- + +The current supported Custom MSR list is: + +MSR_KVM_WALL_CLOCK_NEW: 0x4b564d00 + + data: 4-byte alignment physical address of a memory area which must be + in guest RAM. This memory is expected to hold a copy of the following + structure: + + struct pvclock_wall_clock { + u32 version; + u32 sec; + u32 nsec; + } __attribute__((__packed__)); + + whose data will be filled in by the hypervisor. The hypervisor is only + guaranteed to update this data at the moment of MSR write. + Users that want to reliably query this information more than once have + to write more than once to this MSR. Fields have the following meanings: + + version: guest has to check version before and after grabbing + time information and check that they are both equal and even. + An odd version indicates an in-progress update. + + sec: number of seconds for wallclock at time of boot. + + nsec: number of nanoseconds for wallclock at time of boot. + + In order to get the current wallclock time, the system_time from + MSR_KVM_SYSTEM_TIME_NEW needs to be added. + + Note that although MSRs are per-CPU entities, the effect of this + particular MSR is global. + + Availability of this MSR must be checked via bit 3 in 0x4000001 cpuid + leaf prior to usage. + +MSR_KVM_SYSTEM_TIME_NEW: 0x4b564d01 + + data: 4-byte aligned physical address of a memory area which must be in + guest RAM, plus an enable bit in bit 0. This memory is expected to hold + a copy of the following structure: + + struct pvclock_vcpu_time_info { + u32 version; + u32 pad0; + u64 tsc_timestamp; + u64 system_time; + u32 tsc_to_system_mul; + s8 tsc_shift; + u8 flags; + u8 pad[2]; + } __attribute__((__packed__)); /* 32 bytes */ + + whose data will be filled in by the hypervisor periodically. Only one + write, or registration, is needed for each VCPU. The interval between + updates of this structure is arbitrary and implementation-dependent. + The hypervisor may update this structure at any time it sees fit until + anything with bit0 == 0 is written to it. + + Fields have the following meanings: + + version: guest has to check version before and after grabbing + time information and check that they are both equal and even. + An odd version indicates an in-progress update. + + tsc_timestamp: the tsc value at the current VCPU at the time + of the update of this structure. Guests can subtract this value + from current tsc to derive a notion of elapsed time since the + structure update. + + system_time: a host notion of monotonic time, including sleep + time at the time this structure was last updated. Unit is + nanoseconds. + + tsc_to_system_mul: multiplier to be used when converting + tsc-related quantity to nanoseconds + + tsc_shift: shift to be used when converting tsc-related + quantity to nanoseconds. This shift will ensure that + multiplication with tsc_to_system_mul does not overflow. + A positive value denotes a left shift, a negative value + a right shift. + + The conversion from tsc to nanoseconds involves an additional + right shift by 32 bits. With this information, guests can + derive per-CPU time by doing: + + time = (current_tsc - tsc_timestamp) + if (tsc_shift >= 0) + time <<= tsc_shift; + else + time >>= -tsc_shift; + time = (time * tsc_to_system_mul) >> 32 + time = time + system_time + + flags: bits in this field indicate extended capabilities + coordinated between the guest and the hypervisor. Availability + of specific flags has to be checked in 0x40000001 cpuid leaf. + Current flags are: + + flag bit | cpuid bit | meaning + ------------------------------------------------------------- + | | time measures taken across + 0 | 24 | multiple cpus are guaranteed to + | | be monotonic + ------------------------------------------------------------- + | | guest vcpu has been paused by + 1 | N/A | the host + | | See 4.70 in api.txt + ------------------------------------------------------------- + + Availability of this MSR must be checked via bit 3 in 0x4000001 cpuid + leaf prior to usage. + + +MSR_KVM_WALL_CLOCK: 0x11 + + data and functioning: same as MSR_KVM_WALL_CLOCK_NEW. Use that instead. + + This MSR falls outside the reserved KVM range and may be removed in the + future. Its usage is deprecated. + + Availability of this MSR must be checked via bit 0 in 0x4000001 cpuid + leaf prior to usage. + +MSR_KVM_SYSTEM_TIME: 0x12 + + data and functioning: same as MSR_KVM_SYSTEM_TIME_NEW. Use that instead. + + This MSR falls outside the reserved KVM range and may be removed in the + future. Its usage is deprecated. + + Availability of this MSR must be checked via bit 0 in 0x4000001 cpuid + leaf prior to usage. + + The suggested algorithm for detecting kvmclock presence is then: + + if (!kvm_para_available()) /* refer to cpuid.txt */ + return NON_PRESENT; + + flags = cpuid_eax(0x40000001); + if (flags & 3) { + msr_kvm_system_time = MSR_KVM_SYSTEM_TIME_NEW; + msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK_NEW; + return PRESENT; + } else if (flags & 0) { + msr_kvm_system_time = MSR_KVM_SYSTEM_TIME; + msr_kvm_wall_clock = MSR_KVM_WALL_CLOCK; + return PRESENT; + } else + return NON_PRESENT; + +MSR_KVM_ASYNC_PF_EN: 0x4b564d02 + data: Bits 63-6 hold 64-byte aligned physical address of a + 64 byte memory area which must be in guest RAM and must be + zeroed. Bits 5-3 are reserved and should be zero. Bit 0 is 1 + when asynchronous page faults are enabled on the vcpu 0 when + disabled. Bit 1 is 1 if asynchronous page faults can be injected + when vcpu is in cpl == 0. Bit 2 is 1 if asynchronous page faults + are delivered to L1 as #PF vmexits. Bit 2 can be set only if + KVM_FEATURE_ASYNC_PF_VMEXIT is present in CPUID. + + First 4 byte of 64 byte memory location will be written to by + the hypervisor at the time of asynchronous page fault (APF) + injection to indicate type of asynchronous page fault. Value + of 1 means that the page referred to by the page fault is not + present. Value 2 means that the page is now available. Disabling + interrupt inhibits APFs. Guest must not enable interrupt + before the reason is read, or it may be overwritten by another + APF. Since APF uses the same exception vector as regular page + fault guest must reset the reason to 0 before it does + something that can generate normal page fault. If during page + fault APF reason is 0 it means that this is regular page + fault. + + During delivery of type 1 APF cr2 contains a token that will + be used to notify a guest when missing page becomes + available. When page becomes available type 2 APF is sent with + cr2 set to the token associated with the page. There is special + kind of token 0xffffffff which tells vcpu that it should wake + up all processes waiting for APFs and no individual type 2 APFs + will be sent. + + If APF is disabled while there are outstanding APFs, they will + not be delivered. + + Currently type 2 APF will be always delivered on the same vcpu as + type 1 was, but guest should not rely on that. + +MSR_KVM_STEAL_TIME: 0x4b564d03 + + data: 64-byte alignment physical address of a memory area which must be + in guest RAM, plus an enable bit in bit 0. This memory is expected to + hold a copy of the following structure: + + struct kvm_steal_time { + __u64 steal; + __u32 version; + __u32 flags; + __u8 preempted; + __u8 u8_pad[3]; + __u32 pad[11]; + } + + whose data will be filled in by the hypervisor periodically. Only one + write, or registration, is needed for each VCPU. The interval between + updates of this structure is arbitrary and implementation-dependent. + The hypervisor may update this structure at any time it sees fit until + anything with bit0 == 0 is written to it. Guest is required to make sure + this structure is initialized to zero. + + Fields have the following meanings: + + version: a sequence counter. In other words, guest has to check + this field before and after grabbing time information and make + sure they are both equal and even. An odd version indicates an + in-progress update. + + flags: At this point, always zero. May be used to indicate + changes in this structure in the future. + + steal: the amount of time in which this vCPU did not run, in + nanoseconds. Time during which the vcpu is idle, will not be + reported as steal time. + + preempted: indicate the vCPU who owns this struct is running or + not. Non-zero values mean the vCPU has been preempted. Zero + means the vCPU is not preempted. NOTE, it is always zero if the + the hypervisor doesn't support this field. + +MSR_KVM_EOI_EN: 0x4b564d04 + data: Bit 0 is 1 when PV end of interrupt is enabled on the vcpu; 0 + when disabled. Bit 1 is reserved and must be zero. When PV end of + interrupt is enabled (bit 0 set), bits 63-2 hold a 4-byte aligned + physical address of a 4 byte memory area which must be in guest RAM and + must be zeroed. + + The first, least significant bit of 4 byte memory location will be + written to by the hypervisor, typically at the time of interrupt + injection. Value of 1 means that guest can skip writing EOI to the apic + (using MSR or MMIO write); instead, it is sufficient to signal + EOI by clearing the bit in guest memory - this location will + later be polled by the hypervisor. + Value of 0 means that the EOI write is required. + + It is always safe for the guest to ignore the optimization and perform + the APIC EOI write anyway. + + Hypervisor is guaranteed to only modify this least + significant bit while in the current VCPU context, this means that + guest does not need to use either lock prefix or memory ordering + primitives to synchronise with the hypervisor. + + However, hypervisor can set and clear this memory bit at any time: + therefore to make sure hypervisor does not interrupt the + guest and clear the least significant bit in the memory area + in the window between guest testing it to detect + whether it can skip EOI apic write and between guest + clearing it to signal EOI to the hypervisor, + guest must both read the least significant bit in the memory area and + clear it using a single CPU instruction, such as test and clear, or + compare and exchange. + +MSR_KVM_POLL_CONTROL: 0x4b564d05 + Control host-side polling. + + data: Bit 0 enables (1) or disables (0) host-side HLT polling logic. + + KVM guests can request the host not to poll on HLT, for example if + they are performing polling themselves. + diff --git a/Documentation/virt/kvm/nested-vmx.txt b/Documentation/virt/kvm/nested-vmx.txt new file mode 100644 index 000000000000..97eb1353e962 --- /dev/null +++ b/Documentation/virt/kvm/nested-vmx.txt @@ -0,0 +1,240 @@ +Nested VMX +========== + +Overview +--------- + +On Intel processors, KVM uses Intel's VMX (Virtual-Machine eXtensions) +to easily and efficiently run guest operating systems. Normally, these guests +*cannot* themselves be hypervisors running their own guests, because in VMX, +guests cannot use VMX instructions. + +The "Nested VMX" feature adds this missing capability - of running guest +hypervisors (which use VMX) with their own nested guests. It does so by +allowing a guest to use VMX instructions, and correctly and efficiently +emulating them using the single level of VMX available in the hardware. + +We describe in much greater detail the theory behind the nested VMX feature, +its implementation and its performance characteristics, in the OSDI 2010 paper +"The Turtles Project: Design and Implementation of Nested Virtualization", +available at: + + http://www.usenix.org/events/osdi10/tech/full_papers/Ben-Yehuda.pdf + + +Terminology +----------- + +Single-level virtualization has two levels - the host (KVM) and the guests. +In nested virtualization, we have three levels: The host (KVM), which we call +L0, the guest hypervisor, which we call L1, and its nested guest, which we +call L2. + + +Running nested VMX +------------------ + +The nested VMX feature is disabled by default. It can be enabled by giving +the "nested=1" option to the kvm-intel module. + +No modifications are required to user space (qemu). However, qemu's default +emulated CPU type (qemu64) does not list the "VMX" CPU feature, so it must be +explicitly enabled, by giving qemu one of the following options: + + -cpu host (emulated CPU has all features of the real CPU) + + -cpu qemu64,+vmx (add just the vmx feature to a named CPU type) + + +ABIs +---- + +Nested VMX aims to present a standard and (eventually) fully-functional VMX +implementation for the a guest hypervisor to use. As such, the official +specification of the ABI that it provides is Intel's VMX specification, +namely volume 3B of their "Intel 64 and IA-32 Architectures Software +Developer's Manual". Not all of VMX's features are currently fully supported, +but the goal is to eventually support them all, starting with the VMX features +which are used in practice by popular hypervisors (KVM and others). + +As a VMX implementation, nested VMX presents a VMCS structure to L1. +As mandated by the spec, other than the two fields revision_id and abort, +this structure is *opaque* to its user, who is not supposed to know or care +about its internal structure. Rather, the structure is accessed through the +VMREAD and VMWRITE instructions. +Still, for debugging purposes, KVM developers might be interested to know the +internals of this structure; This is struct vmcs12 from arch/x86/kvm/vmx.c. + +The name "vmcs12" refers to the VMCS that L1 builds for L2. In the code we +also have "vmcs01", the VMCS that L0 built for L1, and "vmcs02" is the VMCS +which L0 builds to actually run L2 - how this is done is explained in the +aforementioned paper. + +For convenience, we repeat the content of struct vmcs12 here. If the internals +of this structure changes, this can break live migration across KVM versions. +VMCS12_REVISION (from vmx.c) should be changed if struct vmcs12 or its inner +struct shadow_vmcs is ever changed. + + typedef u64 natural_width; + struct __packed vmcs12 { + /* According to the Intel spec, a VMCS region must start with + * these two user-visible fields */ + u32 revision_id; + u32 abort; + + u32 launch_state; /* set to 0 by VMCLEAR, to 1 by VMLAUNCH */ + u32 padding[7]; /* room for future expansion */ + + u64 io_bitmap_a; + u64 io_bitmap_b; + u64 msr_bitmap; + u64 vm_exit_msr_store_addr; + u64 vm_exit_msr_load_addr; + u64 vm_entry_msr_load_addr; + u64 tsc_offset; + u64 virtual_apic_page_addr; + u64 apic_access_addr; + u64 ept_pointer; + u64 guest_physical_address; + u64 vmcs_link_pointer; + u64 guest_ia32_debugctl; + u64 guest_ia32_pat; + u64 guest_ia32_efer; + u64 guest_pdptr0; + u64 guest_pdptr1; + u64 guest_pdptr2; + u64 guest_pdptr3; + u64 host_ia32_pat; + u64 host_ia32_efer; + u64 padding64[8]; /* room for future expansion */ + natural_width cr0_guest_host_mask; + natural_width cr4_guest_host_mask; + natural_width cr0_read_shadow; + natural_width cr4_read_shadow; + natural_width cr3_target_value0; + natural_width cr3_target_value1; + natural_width cr3_target_value2; + natural_width cr3_target_value3; + natural_width exit_qualification; + natural_width guest_linear_address; + natural_width guest_cr0; + natural_width guest_cr3; + natural_width guest_cr4; + natural_width guest_es_base; + natural_width guest_cs_base; + natural_width guest_ss_base; + natural_width guest_ds_base; + natural_width guest_fs_base; + natural_width guest_gs_base; + natural_width guest_ldtr_base; + natural_width guest_tr_base; + natural_width guest_gdtr_base; + natural_width guest_idtr_base; + natural_width guest_dr7; + natural_width guest_rsp; + natural_width guest_rip; + natural_width guest_rflags; + natural_width guest_pending_dbg_exceptions; + natural_width guest_sysenter_esp; + natural_width guest_sysenter_eip; + natural_width host_cr0; + natural_width host_cr3; + natural_width host_cr4; + natural_width host_fs_base; + natural_width host_gs_base; + natural_width host_tr_base; + natural_width host_gdtr_base; + natural_width host_idtr_base; + natural_width host_ia32_sysenter_esp; + natural_width host_ia32_sysenter_eip; + natural_width host_rsp; + natural_width host_rip; + natural_width paddingl[8]; /* room for future expansion */ + u32 pin_based_vm_exec_control; + u32 cpu_based_vm_exec_control; + u32 exception_bitmap; + u32 page_fault_error_code_mask; + u32 page_fault_error_code_match; + u32 cr3_target_count; + u32 vm_exit_controls; + u32 vm_exit_msr_store_count; + u32 vm_exit_msr_load_count; + u32 vm_entry_controls; + u32 vm_entry_msr_load_count; + u32 vm_entry_intr_info_field; + u32 vm_entry_exception_error_code; + u32 vm_entry_instruction_len; + u32 tpr_threshold; + u32 secondary_vm_exec_control; + u32 vm_instruction_error; + u32 vm_exit_reason; + u32 vm_exit_intr_info; + u32 vm_exit_intr_error_code; + u32 idt_vectoring_info_field; + u32 idt_vectoring_error_code; + u32 vm_exit_instruction_len; + u32 vmx_instruction_info; + u32 guest_es_limit; + u32 guest_cs_limit; + u32 guest_ss_limit; + u32 guest_ds_limit; + u32 guest_fs_limit; + u32 guest_gs_limit; + u32 guest_ldtr_limit; + u32 guest_tr_limit; + u32 guest_gdtr_limit; + u32 guest_idtr_limit; + u32 guest_es_ar_bytes; + u32 guest_cs_ar_bytes; + u32 guest_ss_ar_bytes; + u32 guest_ds_ar_bytes; + u32 guest_fs_ar_bytes; + u32 guest_gs_ar_bytes; + u32 guest_ldtr_ar_bytes; + u32 guest_tr_ar_bytes; + u32 guest_interruptibility_info; + u32 guest_activity_state; + u32 guest_sysenter_cs; + u32 host_ia32_sysenter_cs; + u32 padding32[8]; /* room for future expansion */ + u16 virtual_processor_id; + u16 guest_es_selector; + u16 guest_cs_selector; + u16 guest_ss_selector; + u16 guest_ds_selector; + u16 guest_fs_selector; + u16 guest_gs_selector; + u16 guest_ldtr_selector; + u16 guest_tr_selector; + u16 host_es_selector; + u16 host_cs_selector; + u16 host_ss_selector; + u16 host_ds_selector; + u16 host_fs_selector; + u16 host_gs_selector; + u16 host_tr_selector; + }; + + +Authors +------- + +These patches were written by: + Abel Gordon, abelg <at> il.ibm.com + Nadav Har'El, nyh <at> il.ibm.com + Orit Wasserman, oritw <at> il.ibm.com + Ben-Ami Yassor, benami <at> il.ibm.com + Muli Ben-Yehuda, muli <at> il.ibm.com + +With contributions by: + Anthony Liguori, aliguori <at> us.ibm.com + Mike Day, mdday <at> us.ibm.com + Michael Factor, factor <at> il.ibm.com + Zvi Dubitzky, dubi <at> il.ibm.com + +And valuable reviews by: + Avi Kivity, avi <at> redhat.com + Gleb Natapov, gleb <at> redhat.com + Marcelo Tosatti, mtosatti <at> redhat.com + Kevin Tian, kevin.tian <at> intel.com + and others. diff --git a/Documentation/virt/kvm/ppc-pv.txt b/Documentation/virt/kvm/ppc-pv.txt new file mode 100644 index 000000000000..e26115ce4258 --- /dev/null +++ b/Documentation/virt/kvm/ppc-pv.txt @@ -0,0 +1,212 @@ +The PPC KVM paravirtual interface +================================= + +The basic execution principle by which KVM on PowerPC works is to run all kernel +space code in PR=1 which is user space. This way we trap all privileged +instructions and can emulate them accordingly. + +Unfortunately that is also the downfall. There are quite some privileged +instructions that needlessly return us to the hypervisor even though they +could be handled differently. + +This is what the PPC PV interface helps with. It takes privileged instructions +and transforms them into unprivileged ones with some help from the hypervisor. +This cuts down virtualization costs by about 50% on some of my benchmarks. + +The code for that interface can be found in arch/powerpc/kernel/kvm* + +Querying for existence +====================== + +To find out if we're running on KVM or not, we leverage the device tree. When +Linux is running on KVM, a node /hypervisor exists. That node contains a +compatible property with the value "linux,kvm". + +Once you determined you're running under a PV capable KVM, you can now use +hypercalls as described below. + +KVM hypercalls +============== + +Inside the device tree's /hypervisor node there's a property called +'hypercall-instructions'. This property contains at most 4 opcodes that make +up the hypercall. To call a hypercall, just call these instructions. + +The parameters are as follows: + + Register IN OUT + + r0 - volatile + r3 1st parameter Return code + r4 2nd parameter 1st output value + r5 3rd parameter 2nd output value + r6 4th parameter 3rd output value + r7 5th parameter 4th output value + r8 6th parameter 5th output value + r9 7th parameter 6th output value + r10 8th parameter 7th output value + r11 hypercall number 8th output value + r12 - volatile + +Hypercall definitions are shared in generic code, so the same hypercall numbers +apply for x86 and powerpc alike with the exception that each KVM hypercall +also needs to be ORed with the KVM vendor code which is (42 << 16). + +Return codes can be as follows: + + Code Meaning + + 0 Success + 12 Hypercall not implemented + <0 Error + +The magic page +============== + +To enable communication between the hypervisor and guest there is a new shared +page that contains parts of supervisor visible register state. The guest can +map this shared page using the KVM hypercall KVM_HC_PPC_MAP_MAGIC_PAGE. + +With this hypercall issued the guest always gets the magic page mapped at the +desired location. The first parameter indicates the effective address when the +MMU is enabled. The second parameter indicates the address in real mode, if +applicable to the target. For now, we always map the page to -4096. This way we +can access it using absolute load and store functions. The following +instruction reads the first field of the magic page: + + ld rX, -4096(0) + +The interface is designed to be extensible should there be need later to add +additional registers to the magic page. If you add fields to the magic page, +also define a new hypercall feature to indicate that the host can give you more +registers. Only if the host supports the additional features, make use of them. + +The magic page layout is described by struct kvm_vcpu_arch_shared +in arch/powerpc/include/asm/kvm_para.h. + +Magic page features +=================== + +When mapping the magic page using the KVM hypercall KVM_HC_PPC_MAP_MAGIC_PAGE, +a second return value is passed to the guest. This second return value contains +a bitmap of available features inside the magic page. + +The following enhancements to the magic page are currently available: + + KVM_MAGIC_FEAT_SR Maps SR registers r/w in the magic page + KVM_MAGIC_FEAT_MAS0_TO_SPRG7 Maps MASn, ESR, PIR and high SPRGs + +For enhanced features in the magic page, please check for the existence of the +feature before using them! + +Magic page flags +================ + +In addition to features that indicate whether a host is capable of a particular +feature we also have a channel for a guest to tell the guest whether it's capable +of something. This is what we call "flags". + +Flags are passed to the host in the low 12 bits of the Effective Address. + +The following flags are currently available for a guest to expose: + + MAGIC_PAGE_FLAG_NOT_MAPPED_NX Guest handles NX bits correctly wrt magic page + +MSR bits +======== + +The MSR contains bits that require hypervisor intervention and bits that do +not require direct hypervisor intervention because they only get interpreted +when entering the guest or don't have any impact on the hypervisor's behavior. + +The following bits are safe to be set inside the guest: + + MSR_EE + MSR_RI + +If any other bit changes in the MSR, please still use mtmsr(d). + +Patched instructions +==================== + +The "ld" and "std" instructions are transformed to "lwz" and "stw" instructions +respectively on 32 bit systems with an added offset of 4 to accommodate for big +endianness. + +The following is a list of mapping the Linux kernel performs when running as +guest. Implementing any of those mappings is optional, as the instruction traps +also act on the shared page. So calling privileged instructions still works as +before. + +From To +==== == + +mfmsr rX ld rX, magic_page->msr +mfsprg rX, 0 ld rX, magic_page->sprg0 +mfsprg rX, 1 ld rX, magic_page->sprg1 +mfsprg rX, 2 ld rX, magic_page->sprg2 +mfsprg rX, 3 ld rX, magic_page->sprg3 +mfsrr0 rX ld rX, magic_page->srr0 +mfsrr1 rX ld rX, magic_page->srr1 +mfdar rX ld rX, magic_page->dar +mfdsisr rX lwz rX, magic_page->dsisr + +mtmsr rX std rX, magic_page->msr +mtsprg 0, rX std rX, magic_page->sprg0 +mtsprg 1, rX std rX, magic_page->sprg1 +mtsprg 2, rX std rX, magic_page->sprg2 +mtsprg 3, rX std rX, magic_page->sprg3 +mtsrr0 rX std rX, magic_page->srr0 +mtsrr1 rX std rX, magic_page->srr1 +mtdar rX std rX, magic_page->dar +mtdsisr rX stw rX, magic_page->dsisr + +tlbsync nop + +mtmsrd rX, 0 b <special mtmsr section> +mtmsr rX b <special mtmsr section> + +mtmsrd rX, 1 b <special mtmsrd section> + +[Book3S only] +mtsrin rX, rY b <special mtsrin section> + +[BookE only] +wrteei [0|1] b <special wrteei section> + + +Some instructions require more logic to determine what's going on than a load +or store instruction can deliver. To enable patching of those, we keep some +RAM around where we can live translate instructions to. What happens is the +following: + + 1) copy emulation code to memory + 2) patch that code to fit the emulated instruction + 3) patch that code to return to the original pc + 4 + 4) patch the original instruction to branch to the new code + +That way we can inject an arbitrary amount of code as replacement for a single +instruction. This allows us to check for pending interrupts when setting EE=1 +for example. + +Hypercall ABIs in KVM on PowerPC +================================= +1) KVM hypercalls (ePAPR) + +These are ePAPR compliant hypercall implementation (mentioned above). Even +generic hypercalls are implemented here, like the ePAPR idle hcall. These are +available on all targets. + +2) PAPR hypercalls + +PAPR hypercalls are needed to run server PowerPC PAPR guests (-M pseries in QEMU). +These are the same hypercalls that pHyp, the POWER hypervisor implements. Some of +them are handled in the kernel, some are handled in user space. This is only +available on book3s_64. + +3) OSI hypercalls + +Mac-on-Linux is another user of KVM on PowerPC, which has its own hypercall (long +before KVM). This is supported to maintain compatibility. All these hypercalls get +forwarded to user space. This is only useful on book3s_32, but can be used with +book3s_64 as well. diff --git a/Documentation/virt/kvm/review-checklist.txt b/Documentation/virt/kvm/review-checklist.txt new file mode 100644 index 000000000000..499af499e296 --- /dev/null +++ b/Documentation/virt/kvm/review-checklist.txt @@ -0,0 +1,38 @@ +Review checklist for kvm patches +================================ + +1. The patch must follow Documentation/process/coding-style.rst and + Documentation/process/submitting-patches.rst. + +2. Patches should be against kvm.git master branch. + +3. If the patch introduces or modifies a new userspace API: + - the API must be documented in Documentation/virt/kvm/api.txt + - the API must be discoverable using KVM_CHECK_EXTENSION + +4. New state must include support for save/restore. + +5. New features must default to off (userspace should explicitly request them). + Performance improvements can and should default to on. + +6. New cpu features should be exposed via KVM_GET_SUPPORTED_CPUID2 + +7. Emulator changes should be accompanied by unit tests for qemu-kvm.git + kvm/test directory. + +8. Changes should be vendor neutral when possible. Changes to common code + are better than duplicating changes to vendor code. + +9. Similarly, prefer changes to arch independent code than to arch dependent + code. + +10. User/kernel interfaces and guest/host interfaces must be 64-bit clean + (all variables and sizes naturally aligned on 64-bit; use specific types + only - u64 rather than ulong). + +11. New guest visible features must either be documented in a hardware manual + or be accompanied by documentation. + +12. Features must be robust against reset and kexec - for example, shared + host/guest memory must be unshared to prevent the host from writing to + guest memory that the guest has not reserved for this purpose. diff --git a/Documentation/virt/kvm/s390-diag.txt b/Documentation/virt/kvm/s390-diag.txt new file mode 100644 index 000000000000..7c52e5f8b210 --- /dev/null +++ b/Documentation/virt/kvm/s390-diag.txt @@ -0,0 +1,83 @@ +The s390 DIAGNOSE call on KVM +============================= + +KVM on s390 supports the DIAGNOSE call for making hypercalls, both for +native hypercalls and for selected hypercalls found on other s390 +hypervisors. + +Note that bits are numbered as by the usual s390 convention (most significant +bit on the left). + + +General remarks +--------------- + +DIAGNOSE calls by the guest cause a mandatory intercept. This implies +all supported DIAGNOSE calls need to be handled by either KVM or its +userspace. + +All DIAGNOSE calls supported by KVM use the RS-a format: + +-------------------------------------- +| '83' | R1 | R3 | B2 | D2 | +-------------------------------------- +0 8 12 16 20 31 + +The second-operand address (obtained by the base/displacement calculation) +is not used to address data. Instead, bits 48-63 of this address specify +the function code, and bits 0-47 are ignored. + +The supported DIAGNOSE function codes vary by the userspace used. For +DIAGNOSE function codes not specific to KVM, please refer to the +documentation for the s390 hypervisors defining them. + + +DIAGNOSE function code 'X'500' - KVM virtio functions +----------------------------------------------------- + +If the function code specifies 0x500, various virtio-related functions +are performed. + +General register 1 contains the virtio subfunction code. Supported +virtio subfunctions depend on KVM's userspace. Generally, userspace +provides either s390-virtio (subcodes 0-2) or virtio-ccw (subcode 3). + +Upon completion of the DIAGNOSE instruction, general register 2 contains +the function's return code, which is either a return code or a subcode +specific value. + +Subcode 0 - s390-virtio notification and early console printk + Handled by userspace. + +Subcode 1 - s390-virtio reset + Handled by userspace. + +Subcode 2 - s390-virtio set status + Handled by userspace. + +Subcode 3 - virtio-ccw notification + Handled by either userspace or KVM (ioeventfd case). + + General register 2 contains a subchannel-identification word denoting + the subchannel of the virtio-ccw proxy device to be notified. + + General register 3 contains the number of the virtqueue to be notified. + + General register 4 contains a 64bit identifier for KVM usage (the + kvm_io_bus cookie). If general register 4 does not contain a valid + identifier, it is ignored. + + After completion of the DIAGNOSE call, general register 2 may contain + a 64bit identifier (in the kvm_io_bus cookie case), or a negative + error value, if an internal error occurred. + + See also the virtio standard for a discussion of this hypercall. + + +DIAGNOSE function code 'X'501 - KVM breakpoint +---------------------------------------------- + +If the function code specifies 0x501, breakpoint functions may be performed. +This function code is handled by userspace. + +This diagnose function code has no subfunctions and uses no parameters. diff --git a/Documentation/virt/kvm/timekeeping.txt b/Documentation/virt/kvm/timekeeping.txt new file mode 100644 index 000000000000..76808a17ad84 --- /dev/null +++ b/Documentation/virt/kvm/timekeeping.txt @@ -0,0 +1,612 @@ + + Timekeeping Virtualization for X86-Based Architectures + + Zachary Amsden <zamsden@redhat.com> + Copyright (c) 2010, Red Hat. All rights reserved. + +1) Overview +2) Timing Devices +3) TSC Hardware +4) Virtualization Problems + +========================================================================= + +1) Overview + +One of the most complicated parts of the X86 platform, and specifically, +the virtualization of this platform is the plethora of timing devices available +and the complexity of emulating those devices. In addition, virtualization of +time introduces a new set of challenges because it introduces a multiplexed +division of time beyond the control of the guest CPU. + +First, we will describe the various timekeeping hardware available, then +present some of the problems which arise and solutions available, giving +specific recommendations for certain classes of KVM guests. + +The purpose of this document is to collect data and information relevant to +timekeeping which may be difficult to find elsewhere, specifically, +information relevant to KVM and hardware-based virtualization. + +========================================================================= + +2) Timing Devices + +First we discuss the basic hardware devices available. TSC and the related +KVM clock are special enough to warrant a full exposition and are described in +the following section. + +2.1) i8254 - PIT + +One of the first timer devices available is the programmable interrupt timer, +or PIT. The PIT has a fixed frequency 1.193182 MHz base clock and three +channels which can be programmed to deliver periodic or one-shot interrupts. +These three channels can be configured in different modes and have individual +counters. Channel 1 and 2 were not available for general use in the original +IBM PC, and historically were connected to control RAM refresh and the PC +speaker. Now the PIT is typically integrated as part of an emulated chipset +and a separate physical PIT is not used. + +The PIT uses I/O ports 0x40 - 0x43. Access to the 16-bit counters is done +using single or multiple byte access to the I/O ports. There are 6 modes +available, but not all modes are available to all timers, as only timer 2 +has a connected gate input, required for modes 1 and 5. The gate line is +controlled by port 61h, bit 0, as illustrated in the following diagram. + + -------------- ---------------- +| | | | +| 1.1932 MHz |---------->| CLOCK OUT | ---------> IRQ 0 +| Clock | | | | + -------------- | +->| GATE TIMER 0 | + | ---------------- + | + | ---------------- + | | | + |------>| CLOCK OUT | ---------> 66.3 KHZ DRAM + | | | (aka /dev/null) + | +->| GATE TIMER 1 | + | ---------------- + | + | ---------------- + | | | + |------>| CLOCK OUT | ---------> Port 61h, bit 5 + | | | +Port 61h, bit 0 ---------->| GATE TIMER 2 | \_.---- ____ + ---------------- _| )--|LPF|---Speaker + / *---- \___/ +Port 61h, bit 1 -----------------------------------/ + +The timer modes are now described. + +Mode 0: Single Timeout. This is a one-shot software timeout that counts down + when the gate is high (always true for timers 0 and 1). When the count + reaches zero, the output goes high. + +Mode 1: Triggered One-shot. The output is initially set high. When the gate + line is set high, a countdown is initiated (which does not stop if the gate is + lowered), during which the output is set low. When the count reaches zero, + the output goes high. + +Mode 2: Rate Generator. The output is initially set high. When the countdown + reaches 1, the output goes low for one count and then returns high. The value + is reloaded and the countdown automatically resumes. If the gate line goes + low, the count is halted. If the output is low when the gate is lowered, the + output automatically goes high (this only affects timer 2). + +Mode 3: Square Wave. This generates a high / low square wave. The count + determines the length of the pulse, which alternates between high and low + when zero is reached. The count only proceeds when gate is high and is + automatically reloaded on reaching zero. The count is decremented twice at + each clock to generate a full high / low cycle at the full periodic rate. + If the count is even, the clock remains high for N/2 counts and low for N/2 + counts; if the clock is odd, the clock is high for (N+1)/2 counts and low + for (N-1)/2 counts. Only even values are latched by the counter, so odd + values are not observed when reading. This is the intended mode for timer 2, + which generates sine-like tones by low-pass filtering the square wave output. + +Mode 4: Software Strobe. After programming this mode and loading the counter, + the output remains high until the counter reaches zero. Then the output + goes low for 1 clock cycle and returns high. The counter is not reloaded. + Counting only occurs when gate is high. + +Mode 5: Hardware Strobe. After programming and loading the counter, the + output remains high. When the gate is raised, a countdown is initiated + (which does not stop if the gate is lowered). When the counter reaches zero, + the output goes low for 1 clock cycle and then returns high. The counter is + not reloaded. + +In addition to normal binary counting, the PIT supports BCD counting. The +command port, 0x43 is used to set the counter and mode for each of the three +timers. + +PIT commands, issued to port 0x43, using the following bit encoding: + +Bit 7-4: Command (See table below) +Bit 3-1: Mode (000 = Mode 0, 101 = Mode 5, 11X = undefined) +Bit 0 : Binary (0) / BCD (1) + +Command table: + +0000 - Latch Timer 0 count for port 0x40 + sample and hold the count to be read in port 0x40; + additional commands ignored until counter is read; + mode bits ignored. + +0001 - Set Timer 0 LSB mode for port 0x40 + set timer to read LSB only and force MSB to zero; + mode bits set timer mode + +0010 - Set Timer 0 MSB mode for port 0x40 + set timer to read MSB only and force LSB to zero; + mode bits set timer mode + +0011 - Set Timer 0 16-bit mode for port 0x40 + set timer to read / write LSB first, then MSB; + mode bits set timer mode + +0100 - Latch Timer 1 count for port 0x41 - as described above +0101 - Set Timer 1 LSB mode for port 0x41 - as described above +0110 - Set Timer 1 MSB mode for port 0x41 - as described above +0111 - Set Timer 1 16-bit mode for port 0x41 - as described above + +1000 - Latch Timer 2 count for port 0x42 - as described above +1001 - Set Timer 2 LSB mode for port 0x42 - as described above +1010 - Set Timer 2 MSB mode for port 0x42 - as described above +1011 - Set Timer 2 16-bit mode for port 0x42 as described above + +1101 - General counter latch + Latch combination of counters into corresponding ports + Bit 3 = Counter 2 + Bit 2 = Counter 1 + Bit 1 = Counter 0 + Bit 0 = Unused + +1110 - Latch timer status + Latch combination of counter mode into corresponding ports + Bit 3 = Counter 2 + Bit 2 = Counter 1 + Bit 1 = Counter 0 + + The output of ports 0x40-0x42 following this command will be: + + Bit 7 = Output pin + Bit 6 = Count loaded (0 if timer has expired) + Bit 5-4 = Read / Write mode + 01 = MSB only + 10 = LSB only + 11 = LSB / MSB (16-bit) + Bit 3-1 = Mode + Bit 0 = Binary (0) / BCD mode (1) + +2.2) RTC + +The second device which was available in the original PC was the MC146818 real +time clock. The original device is now obsolete, and usually emulated by the +system chipset, sometimes by an HPET and some frankenstein IRQ routing. + +The RTC is accessed through CMOS variables, which uses an index register to +control which bytes are read. Since there is only one index register, read +of the CMOS and read of the RTC require lock protection (in addition, it is +dangerous to allow userspace utilities such as hwclock to have direct RTC +access, as they could corrupt kernel reads and writes of CMOS memory). + +The RTC generates an interrupt which is usually routed to IRQ 8. The interrupt +can function as a periodic timer, an additional once a day alarm, and can issue +interrupts after an update of the CMOS registers by the MC146818 is complete. +The type of interrupt is signalled in the RTC status registers. + +The RTC will update the current time fields by battery power even while the +system is off. The current time fields should not be read while an update is +in progress, as indicated in the status register. + +The clock uses a 32.768kHz crystal, so bits 6-4 of register A should be +programmed to a 32kHz divider if the RTC is to count seconds. + +This is the RAM map originally used for the RTC/CMOS: + +Location Size Description +------------------------------------------ +00h byte Current second (BCD) +01h byte Seconds alarm (BCD) +02h byte Current minute (BCD) +03h byte Minutes alarm (BCD) +04h byte Current hour (BCD) +05h byte Hours alarm (BCD) +06h byte Current day of week (BCD) +07h byte Current day of month (BCD) +08h byte Current month (BCD) +09h byte Current year (BCD) +0Ah byte Register A + bit 7 = Update in progress + bit 6-4 = Divider for clock + 000 = 4.194 MHz + 001 = 1.049 MHz + 010 = 32 kHz + 10X = test modes + 110 = reset / disable + 111 = reset / disable + bit 3-0 = Rate selection for periodic interrupt + 000 = periodic timer disabled + 001 = 3.90625 uS + 010 = 7.8125 uS + 011 = .122070 mS + 100 = .244141 mS + ... + 1101 = 125 mS + 1110 = 250 mS + 1111 = 500 mS +0Bh byte Register B + bit 7 = Run (0) / Halt (1) + bit 6 = Periodic interrupt enable + bit 5 = Alarm interrupt enable + bit 4 = Update-ended interrupt enable + bit 3 = Square wave interrupt enable + bit 2 = BCD calendar (0) / Binary (1) + bit 1 = 12-hour mode (0) / 24-hour mode (1) + bit 0 = 0 (DST off) / 1 (DST enabled) +OCh byte Register C (read only) + bit 7 = interrupt request flag (IRQF) + bit 6 = periodic interrupt flag (PF) + bit 5 = alarm interrupt flag (AF) + bit 4 = update interrupt flag (UF) + bit 3-0 = reserved +ODh byte Register D (read only) + bit 7 = RTC has power + bit 6-0 = reserved +32h byte Current century BCD (*) + (*) location vendor specific and now determined from ACPI global tables + +2.3) APIC + +On Pentium and later processors, an on-board timer is available to each CPU +as part of the Advanced Programmable Interrupt Controller. The APIC is +accessed through memory-mapped registers and provides interrupt service to each +CPU, used for IPIs and local timer interrupts. + +Although in theory the APIC is a safe and stable source for local interrupts, +in practice, many bugs and glitches have occurred due to the special nature of +the APIC CPU-local memory-mapped hardware. Beware that CPU errata may affect +the use of the APIC and that workarounds may be required. In addition, some of +these workarounds pose unique constraints for virtualization - requiring either +extra overhead incurred from extra reads of memory-mapped I/O or additional +functionality that may be more computationally expensive to implement. + +Since the APIC is documented quite well in the Intel and AMD manuals, we will +avoid repetition of the detail here. It should be pointed out that the APIC +timer is programmed through the LVT (local vector timer) register, is capable +of one-shot or periodic operation, and is based on the bus clock divided down +by the programmable divider register. + +2.4) HPET + +HPET is quite complex, and was originally intended to replace the PIT / RTC +support of the X86 PC. It remains to be seen whether that will be the case, as +the de facto standard of PC hardware is to emulate these older devices. Some +systems designated as legacy free may support only the HPET as a hardware timer +device. + +The HPET spec is rather loose and vague, requiring at least 3 hardware timers, +but allowing implementation freedom to support many more. It also imposes no +fixed rate on the timer frequency, but does impose some extremal values on +frequency, error and slew. + +In general, the HPET is recommended as a high precision (compared to PIT /RTC) +time source which is independent of local variation (as there is only one HPET +in any given system). The HPET is also memory-mapped, and its presence is +indicated through ACPI tables by the BIOS. + +Detailed specification of the HPET is beyond the current scope of this +document, as it is also very well documented elsewhere. + +2.5) Offboard Timers + +Several cards, both proprietary (watchdog boards) and commonplace (e1000) have +timing chips built into the cards which may have registers which are accessible +to kernel or user drivers. To the author's knowledge, using these to generate +a clocksource for a Linux or other kernel has not yet been attempted and is in +general frowned upon as not playing by the agreed rules of the game. Such a +timer device would require additional support to be virtualized properly and is +not considered important at this time as no known operating system does this. + +========================================================================= + +3) TSC Hardware + +The TSC or time stamp counter is relatively simple in theory; it counts +instruction cycles issued by the processor, which can be used as a measure of +time. In practice, due to a number of problems, it is the most complicated +timekeeping device to use. + +The TSC is represented internally as a 64-bit MSR which can be read with the +RDMSR, RDTSC, or RDTSCP (when available) instructions. In the past, hardware +limitations made it possible to write the TSC, but generally on old hardware it +was only possible to write the low 32-bits of the 64-bit counter, and the upper +32-bits of the counter were cleared. Now, however, on Intel processors family +0Fh, for models 3, 4 and 6, and family 06h, models e and f, this restriction +has been lifted and all 64-bits are writable. On AMD systems, the ability to +write the TSC MSR is not an architectural guarantee. + +The TSC is accessible from CPL-0 and conditionally, for CPL > 0 software by +means of the CR4.TSD bit, which when enabled, disables CPL > 0 TSC access. + +Some vendors have implemented an additional instruction, RDTSCP, which returns +atomically not just the TSC, but an indicator which corresponds to the +processor number. This can be used to index into an array of TSC variables to +determine offset information in SMP systems where TSCs are not synchronized. +The presence of this instruction must be determined by consulting CPUID feature +bits. + +Both VMX and SVM provide extension fields in the virtualization hardware which +allows the guest visible TSC to be offset by a constant. Newer implementations +promise to allow the TSC to additionally be scaled, but this hardware is not +yet widely available. + +3.1) TSC synchronization + +The TSC is a CPU-local clock in most implementations. This means, on SMP +platforms, the TSCs of different CPUs may start at different times depending +on when the CPUs are powered on. Generally, CPUs on the same die will share +the same clock, however, this is not always the case. + +The BIOS may attempt to resynchronize the TSCs during the poweron process and +the operating system or other system software may attempt to do this as well. +Several hardware limitations make the problem worse - if it is not possible to +write the full 64-bits of the TSC, it may be impossible to match the TSC in +newly arriving CPUs to that of the rest of the system, resulting in +unsynchronized TSCs. This may be done by BIOS or system software, but in +practice, getting a perfectly synchronized TSC will not be possible unless all +values are read from the same clock, which generally only is possible on single +socket systems or those with special hardware support. + +3.2) TSC and CPU hotplug + +As touched on already, CPUs which arrive later than the boot time of the system +may not have a TSC value that is synchronized with the rest of the system. +Either system software, BIOS, or SMM code may actually try to establish the TSC +to a value matching the rest of the system, but a perfect match is usually not +a guarantee. This can have the effect of bringing a system from a state where +TSC is synchronized back to a state where TSC synchronization flaws, however +small, may be exposed to the OS and any virtualization environment. + +3.3) TSC and multi-socket / NUMA + +Multi-socket systems, especially large multi-socket systems are likely to have +individual clocksources rather than a single, universally distributed clock. +Since these clocks are driven by different crystals, they will not have +perfectly matched frequency, and temperature and electrical variations will +cause the CPU clocks, and thus the TSCs to drift over time. Depending on the +exact clock and bus design, the drift may or may not be fixed in absolute +error, and may accumulate over time. + +In addition, very large systems may deliberately slew the clocks of individual +cores. This technique, known as spread-spectrum clocking, reduces EMI at the +clock frequency and harmonics of it, which may be required to pass FCC +standards for telecommunications and computer equipment. + +It is recommended not to trust the TSCs to remain synchronized on NUMA or +multiple socket systems for these reasons. + +3.4) TSC and C-states + +C-states, or idling states of the processor, especially C1E and deeper sleep +states may be problematic for TSC as well. The TSC may stop advancing in such +a state, resulting in a TSC which is behind that of other CPUs when execution +is resumed. Such CPUs must be detected and flagged by the operating system +based on CPU and chipset identifications. + +The TSC in such a case may be corrected by catching it up to a known external +clocksource. + +3.5) TSC frequency change / P-states + +To make things slightly more interesting, some CPUs may change frequency. They +may or may not run the TSC at the same rate, and because the frequency change +may be staggered or slewed, at some points in time, the TSC rate may not be +known other than falling within a range of values. In this case, the TSC will +not be a stable time source, and must be calibrated against a known, stable, +external clock to be a usable source of time. + +Whether the TSC runs at a constant rate or scales with the P-state is model +dependent and must be determined by inspecting CPUID, chipset or vendor +specific MSR fields. + +In addition, some vendors have known bugs where the P-state is actually +compensated for properly during normal operation, but when the processor is +inactive, the P-state may be raised temporarily to service cache misses from +other processors. In such cases, the TSC on halted CPUs could advance faster +than that of non-halted processors. AMD Turion processors are known to have +this problem. + +3.6) TSC and STPCLK / T-states + +External signals given to the processor may also have the effect of stopping +the TSC. This is typically done for thermal emergency power control to prevent +an overheating condition, and typically, there is no way to detect that this +condition has happened. + +3.7) TSC virtualization - VMX + +VMX provides conditional trapping of RDTSC, RDMSR, WRMSR and RDTSCP +instructions, which is enough for full virtualization of TSC in any manner. In +addition, VMX allows passing through the host TSC plus an additional TSC_OFFSET +field specified in the VMCS. Special instructions must be used to read and +write the VMCS field. + +3.8) TSC virtualization - SVM + +SVM provides conditional trapping of RDTSC, RDMSR, WRMSR and RDTSCP +instructions, which is enough for full virtualization of TSC in any manner. In +addition, SVM allows passing through the host TSC plus an additional offset +field specified in the SVM control block. + +3.9) TSC feature bits in Linux + +In summary, there is no way to guarantee the TSC remains in perfect +synchronization unless it is explicitly guaranteed by the architecture. Even +if so, the TSCs in multi-sockets or NUMA systems may still run independently +despite being locally consistent. + +The following feature bits are used by Linux to signal various TSC attributes, +but they can only be taken to be meaningful for UP or single node systems. + +X86_FEATURE_TSC : The TSC is available in hardware +X86_FEATURE_RDTSCP : The RDTSCP instruction is available +X86_FEATURE_CONSTANT_TSC : The TSC rate is unchanged with P-states +X86_FEATURE_NONSTOP_TSC : The TSC does not stop in C-states +X86_FEATURE_TSC_RELIABLE : TSC sync checks are skipped (VMware) + +4) Virtualization Problems + +Timekeeping is especially problematic for virtualization because a number of +challenges arise. The most obvious problem is that time is now shared between +the host and, potentially, a number of virtual machines. Thus the virtual +operating system does not run with 100% usage of the CPU, despite the fact that +it may very well make that assumption. It may expect it to remain true to very +exacting bounds when interrupt sources are disabled, but in reality only its +virtual interrupt sources are disabled, and the machine may still be preempted +at any time. This causes problems as the passage of real time, the injection +of machine interrupts and the associated clock sources are no longer completely +synchronized with real time. + +This same problem can occur on native hardware to a degree, as SMM mode may +steal cycles from the naturally on X86 systems when SMM mode is used by the +BIOS, but not in such an extreme fashion. However, the fact that SMM mode may +cause similar problems to virtualization makes it a good justification for +solving many of these problems on bare metal. + +4.1) Interrupt clocking + +One of the most immediate problems that occurs with legacy operating systems +is that the system timekeeping routines are often designed to keep track of +time by counting periodic interrupts. These interrupts may come from the PIT +or the RTC, but the problem is the same: the host virtualization engine may not +be able to deliver the proper number of interrupts per second, and so guest +time may fall behind. This is especially problematic if a high interrupt rate +is selected, such as 1000 HZ, which is unfortunately the default for many Linux +guests. + +There are three approaches to solving this problem; first, it may be possible +to simply ignore it. Guests which have a separate time source for tracking +'wall clock' or 'real time' may not need any adjustment of their interrupts to +maintain proper time. If this is not sufficient, it may be necessary to inject +additional interrupts into the guest in order to increase the effective +interrupt rate. This approach leads to complications in extreme conditions, +where host load or guest lag is too much to compensate for, and thus another +solution to the problem has risen: the guest may need to become aware of lost +ticks and compensate for them internally. Although promising in theory, the +implementation of this policy in Linux has been extremely error prone, and a +number of buggy variants of lost tick compensation are distributed across +commonly used Linux systems. + +Windows uses periodic RTC clocking as a means of keeping time internally, and +thus requires interrupt slewing to keep proper time. It does use a low enough +rate (ed: is it 18.2 Hz?) however that it has not yet been a problem in +practice. + +4.2) TSC sampling and serialization + +As the highest precision time source available, the cycle counter of the CPU +has aroused much interest from developers. As explained above, this timer has +many problems unique to its nature as a local, potentially unstable and +potentially unsynchronized source. One issue which is not unique to the TSC, +but is highlighted because of its very precise nature is sampling delay. By +definition, the counter, once read is already old. However, it is also +possible for the counter to be read ahead of the actual use of the result. +This is a consequence of the superscalar execution of the instruction stream, +which may execute instructions out of order. Such execution is called +non-serialized. Forcing serialized execution is necessary for precise +measurement with the TSC, and requires a serializing instruction, such as CPUID +or an MSR read. + +Since CPUID may actually be virtualized by a trap and emulate mechanism, this +serialization can pose a performance issue for hardware virtualization. An +accurate time stamp counter reading may therefore not always be available, and +it may be necessary for an implementation to guard against "backwards" reads of +the TSC as seen from other CPUs, even in an otherwise perfectly synchronized +system. + +4.3) Timespec aliasing + +Additionally, this lack of serialization from the TSC poses another challenge +when using results of the TSC when measured against another time source. As +the TSC is much higher precision, many possible values of the TSC may be read +while another clock is still expressing the same value. + +That is, you may read (T,T+10) while external clock C maintains the same value. +Due to non-serialized reads, you may actually end up with a range which +fluctuates - from (T-1.. T+10). Thus, any time calculated from a TSC, but +calibrated against an external value may have a range of valid values. +Re-calibrating this computation may actually cause time, as computed after the +calibration, to go backwards, compared with time computed before the +calibration. + +This problem is particularly pronounced with an internal time source in Linux, +the kernel time, which is expressed in the theoretically high resolution +timespec - but which advances in much larger granularity intervals, sometimes +at the rate of jiffies, and possibly in catchup modes, at a much larger step. + +This aliasing requires care in the computation and recalibration of kvmclock +and any other values derived from TSC computation (such as TSC virtualization +itself). + +4.4) Migration + +Migration of a virtual machine raises problems for timekeeping in two ways. +First, the migration itself may take time, during which interrupts cannot be +delivered, and after which, the guest time may need to be caught up. NTP may +be able to help to some degree here, as the clock correction required is +typically small enough to fall in the NTP-correctable window. + +An additional concern is that timers based off the TSC (or HPET, if the raw bus +clock is exposed) may now be running at different rates, requiring compensation +in some way in the hypervisor by virtualizing these timers. In addition, +migrating to a faster machine may preclude the use of a passthrough TSC, as a +faster clock cannot be made visible to a guest without the potential of time +advancing faster than usual. A slower clock is less of a problem, as it can +always be caught up to the original rate. KVM clock avoids these problems by +simply storing multipliers and offsets against the TSC for the guest to convert +back into nanosecond resolution values. + +4.5) Scheduling + +Since scheduling may be based on precise timing and firing of interrupts, the +scheduling algorithms of an operating system may be adversely affected by +virtualization. In theory, the effect is random and should be universally +distributed, but in contrived as well as real scenarios (guest device access, +causes of virtualization exits, possible context switch), this may not always +be the case. The effect of this has not been well studied. + +In an attempt to work around this, several implementations have provided a +paravirtualized scheduler clock, which reveals the true amount of CPU time for +which a virtual machine has been running. + +4.6) Watchdogs + +Watchdog timers, such as the lock detector in Linux may fire accidentally when +running under hardware virtualization due to timer interrupts being delayed or +misinterpretation of the passage of real time. Usually, these warnings are +spurious and can be ignored, but in some circumstances it may be necessary to +disable such detection. + +4.7) Delays and precision timing + +Precise timing and delays may not be possible in a virtualized system. This +can happen if the system is controlling physical hardware, or issues delays to +compensate for slower I/O to and from devices. The first issue is not solvable +in general for a virtualized system; hardware control software can't be +adequately virtualized without a full real-time operating system, which would +require an RT aware virtualization platform. + +The second issue may cause performance problems, but this is unlikely to be a +significant issue. In many cases these delays may be eliminated through +configuration or paravirtualization. + +4.8) Covert channels and leaks + +In addition to the above problems, time information will inevitably leak to the +guest about the host in anything but a perfect implementation of virtualized +time. This may allow the guest to infer the presence of a hypervisor (as in a +red-pill type detection), and it may allow information to leak between guests +by using CPU utilization itself as a signalling channel. Preventing such +problems would require completely isolated virtual time which may not track +real time any longer. This may be useful in certain security or QA contexts, +but in general isn't recommended for real-world deployment scenarios. diff --git a/Documentation/virt/kvm/vcpu-requests.rst b/Documentation/virt/kvm/vcpu-requests.rst new file mode 100644 index 000000000000..5feb3706a7ae --- /dev/null +++ b/Documentation/virt/kvm/vcpu-requests.rst @@ -0,0 +1,307 @@ +================= +KVM VCPU Requests +================= + +Overview +======== + +KVM supports an internal API enabling threads to request a VCPU thread to +perform some activity. For example, a thread may request a VCPU to flush +its TLB with a VCPU request. The API consists of the following functions:: + + /* Check if any requests are pending for VCPU @vcpu. */ + bool kvm_request_pending(struct kvm_vcpu *vcpu); + + /* Check if VCPU @vcpu has request @req pending. */ + bool kvm_test_request(int req, struct kvm_vcpu *vcpu); + + /* Clear request @req for VCPU @vcpu. */ + void kvm_clear_request(int req, struct kvm_vcpu *vcpu); + + /* + * Check if VCPU @vcpu has request @req pending. When the request is + * pending it will be cleared and a memory barrier, which pairs with + * another in kvm_make_request(), will be issued. + */ + bool kvm_check_request(int req, struct kvm_vcpu *vcpu); + + /* + * Make request @req of VCPU @vcpu. Issues a memory barrier, which pairs + * with another in kvm_check_request(), prior to setting the request. + */ + void kvm_make_request(int req, struct kvm_vcpu *vcpu); + + /* Make request @req of all VCPUs of the VM with struct kvm @kvm. */ + bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req); + +Typically a requester wants the VCPU to perform the activity as soon +as possible after making the request. This means most requests +(kvm_make_request() calls) are followed by a call to kvm_vcpu_kick(), +and kvm_make_all_cpus_request() has the kicking of all VCPUs built +into it. + +VCPU Kicks +---------- + +The goal of a VCPU kick is to bring a VCPU thread out of guest mode in +order to perform some KVM maintenance. To do so, an IPI is sent, forcing +a guest mode exit. However, a VCPU thread may not be in guest mode at the +time of the kick. Therefore, depending on the mode and state of the VCPU +thread, there are two other actions a kick may take. All three actions +are listed below: + +1) Send an IPI. This forces a guest mode exit. +2) Waking a sleeping VCPU. Sleeping VCPUs are VCPU threads outside guest + mode that wait on waitqueues. Waking them removes the threads from + the waitqueues, allowing the threads to run again. This behavior + may be suppressed, see KVM_REQUEST_NO_WAKEUP below. +3) Nothing. When the VCPU is not in guest mode and the VCPU thread is not + sleeping, then there is nothing to do. + +VCPU Mode +--------- + +VCPUs have a mode state, ``vcpu->mode``, that is used to track whether the +guest is running in guest mode or not, as well as some specific +outside guest mode states. The architecture may use ``vcpu->mode`` to +ensure VCPU requests are seen by VCPUs (see "Ensuring Requests Are Seen"), +as well as to avoid sending unnecessary IPIs (see "IPI Reduction"), and +even to ensure IPI acknowledgements are waited upon (see "Waiting for +Acknowledgements"). The following modes are defined: + +OUTSIDE_GUEST_MODE + + The VCPU thread is outside guest mode. + +IN_GUEST_MODE + + The VCPU thread is in guest mode. + +EXITING_GUEST_MODE + + The VCPU thread is transitioning from IN_GUEST_MODE to + OUTSIDE_GUEST_MODE. + +READING_SHADOW_PAGE_TABLES + + The VCPU thread is outside guest mode, but it wants the sender of + certain VCPU requests, namely KVM_REQ_TLB_FLUSH, to wait until the VCPU + thread is done reading the page tables. + +VCPU Request Internals +====================== + +VCPU requests are simply bit indices of the ``vcpu->requests`` bitmap. +This means general bitops, like those documented in [atomic-ops]_ could +also be used, e.g. :: + + clear_bit(KVM_REQ_UNHALT & KVM_REQUEST_MASK, &vcpu->requests); + +However, VCPU request users should refrain from doing so, as it would +break the abstraction. The first 8 bits are reserved for architecture +independent requests, all additional bits are available for architecture +dependent requests. + +Architecture Independent Requests +--------------------------------- + +KVM_REQ_TLB_FLUSH + + KVM's common MMU notifier may need to flush all of a guest's TLB + entries, calling kvm_flush_remote_tlbs() to do so. Architectures that + choose to use the common kvm_flush_remote_tlbs() implementation will + need to handle this VCPU request. + +KVM_REQ_MMU_RELOAD + + When shadow page tables are used and memory slots are removed it's + necessary to inform each VCPU to completely refresh the tables. This + request is used for that. + +KVM_REQ_PENDING_TIMER + + This request may be made from a timer handler run on the host on behalf + of a VCPU. It informs the VCPU thread to inject a timer interrupt. + +KVM_REQ_UNHALT + + This request may be made from the KVM common function kvm_vcpu_block(), + which is used to emulate an instruction that causes a CPU to halt until + one of an architectural specific set of events and/or interrupts is + received (determined by checking kvm_arch_vcpu_runnable()). When that + event or interrupt arrives kvm_vcpu_block() makes the request. This is + in contrast to when kvm_vcpu_block() returns due to any other reason, + such as a pending signal, which does not indicate the VCPU's halt + emulation should stop, and therefore does not make the request. + +KVM_REQUEST_MASK +---------------- + +VCPU requests should be masked by KVM_REQUEST_MASK before using them with +bitops. This is because only the lower 8 bits are used to represent the +request's number. The upper bits are used as flags. Currently only two +flags are defined. + +VCPU Request Flags +------------------ + +KVM_REQUEST_NO_WAKEUP + + This flag is applied to requests that only need immediate attention + from VCPUs running in guest mode. That is, sleeping VCPUs do not need + to be awaken for these requests. Sleeping VCPUs will handle the + requests when they are awaken later for some other reason. + +KVM_REQUEST_WAIT + + When requests with this flag are made with kvm_make_all_cpus_request(), + then the caller will wait for each VCPU to acknowledge its IPI before + proceeding. This flag only applies to VCPUs that would receive IPIs. + If, for example, the VCPU is sleeping, so no IPI is necessary, then + the requesting thread does not wait. This means that this flag may be + safely combined with KVM_REQUEST_NO_WAKEUP. See "Waiting for + Acknowledgements" for more information about requests with + KVM_REQUEST_WAIT. + +VCPU Requests with Associated State +=================================== + +Requesters that want the receiving VCPU to handle new state need to ensure +the newly written state is observable to the receiving VCPU thread's CPU +by the time it observes the request. This means a write memory barrier +must be inserted after writing the new state and before setting the VCPU +request bit. Additionally, on the receiving VCPU thread's side, a +corresponding read barrier must be inserted after reading the request bit +and before proceeding to read the new state associated with it. See +scenario 3, Message and Flag, of [lwn-mb]_ and the kernel documentation +[memory-barriers]_. + +The pair of functions, kvm_check_request() and kvm_make_request(), provide +the memory barriers, allowing this requirement to be handled internally by +the API. + +Ensuring Requests Are Seen +========================== + +When making requests to VCPUs, we want to avoid the receiving VCPU +executing in guest mode for an arbitrary long time without handling the +request. We can be sure this won't happen as long as we ensure the VCPU +thread checks kvm_request_pending() before entering guest mode and that a +kick will send an IPI to force an exit from guest mode when necessary. +Extra care must be taken to cover the period after the VCPU thread's last +kvm_request_pending() check and before it has entered guest mode, as kick +IPIs will only trigger guest mode exits for VCPU threads that are in guest +mode or at least have already disabled interrupts in order to prepare to +enter guest mode. This means that an optimized implementation (see "IPI +Reduction") must be certain when it's safe to not send the IPI. One +solution, which all architectures except s390 apply, is to: + +- set ``vcpu->mode`` to IN_GUEST_MODE between disabling the interrupts and + the last kvm_request_pending() check; +- enable interrupts atomically when entering the guest. + +This solution also requires memory barriers to be placed carefully in both +the requesting thread and the receiving VCPU. With the memory barriers we +can exclude the possibility of a VCPU thread observing +!kvm_request_pending() on its last check and then not receiving an IPI for +the next request made of it, even if the request is made immediately after +the check. This is done by way of the Dekker memory barrier pattern +(scenario 10 of [lwn-mb]_). As the Dekker pattern requires two variables, +this solution pairs ``vcpu->mode`` with ``vcpu->requests``. Substituting +them into the pattern gives:: + + CPU1 CPU2 + ================= ================= + local_irq_disable(); + WRITE_ONCE(vcpu->mode, IN_GUEST_MODE); kvm_make_request(REQ, vcpu); + smp_mb(); smp_mb(); + if (kvm_request_pending(vcpu)) { if (READ_ONCE(vcpu->mode) == + IN_GUEST_MODE) { + ...abort guest entry... ...send IPI... + } } + +As stated above, the IPI is only useful for VCPU threads in guest mode or +that have already disabled interrupts. This is why this specific case of +the Dekker pattern has been extended to disable interrupts before setting +``vcpu->mode`` to IN_GUEST_MODE. WRITE_ONCE() and READ_ONCE() are used to +pedantically implement the memory barrier pattern, guaranteeing the +compiler doesn't interfere with ``vcpu->mode``'s carefully planned +accesses. + +IPI Reduction +------------- + +As only one IPI is needed to get a VCPU to check for any/all requests, +then they may be coalesced. This is easily done by having the first IPI +sending kick also change the VCPU mode to something !IN_GUEST_MODE. The +transitional state, EXITING_GUEST_MODE, is used for this purpose. + +Waiting for Acknowledgements +---------------------------- + +Some requests, those with the KVM_REQUEST_WAIT flag set, require IPIs to +be sent, and the acknowledgements to be waited upon, even when the target +VCPU threads are in modes other than IN_GUEST_MODE. For example, one case +is when a target VCPU thread is in READING_SHADOW_PAGE_TABLES mode, which +is set after disabling interrupts. To support these cases, the +KVM_REQUEST_WAIT flag changes the condition for sending an IPI from +checking that the VCPU is IN_GUEST_MODE to checking that it is not +OUTSIDE_GUEST_MODE. + +Request-less VCPU Kicks +----------------------- + +As the determination of whether or not to send an IPI depends on the +two-variable Dekker memory barrier pattern, then it's clear that +request-less VCPU kicks are almost never correct. Without the assurance +that a non-IPI generating kick will still result in an action by the +receiving VCPU, as the final kvm_request_pending() check does for +request-accompanying kicks, then the kick may not do anything useful at +all. If, for instance, a request-less kick was made to a VCPU that was +just about to set its mode to IN_GUEST_MODE, meaning no IPI is sent, then +the VCPU thread may continue its entry without actually having done +whatever it was the kick was meant to initiate. + +One exception is x86's posted interrupt mechanism. In this case, however, +even the request-less VCPU kick is coupled with the same +local_irq_disable() + smp_mb() pattern described above; the ON bit +(Outstanding Notification) in the posted interrupt descriptor takes the +role of ``vcpu->requests``. When sending a posted interrupt, PIR.ON is +set before reading ``vcpu->mode``; dually, in the VCPU thread, +vmx_sync_pir_to_irr() reads PIR after setting ``vcpu->mode`` to +IN_GUEST_MODE. + +Additional Considerations +========================= + +Sleeping VCPUs +-------------- + +VCPU threads may need to consider requests before and/or after calling +functions that may put them to sleep, e.g. kvm_vcpu_block(). Whether they +do or not, and, if they do, which requests need consideration, is +architecture dependent. kvm_vcpu_block() calls kvm_arch_vcpu_runnable() +to check if it should awaken. One reason to do so is to provide +architectures a function where requests may be checked if necessary. + +Clearing Requests +----------------- + +Generally it only makes sense for the receiving VCPU thread to clear a +request. However, in some circumstances, such as when the requesting +thread and the receiving VCPU thread are executed serially, such as when +they are the same thread, or when they are using some form of concurrency +control to temporarily execute synchronously, then it's possible to know +that the request may be cleared immediately, rather than waiting for the +receiving VCPU thread to handle the request in VCPU RUN. The only current +examples of this are kvm_vcpu_block() calls made by VCPUs to block +themselves. A possible side-effect of that call is to make the +KVM_REQ_UNHALT request, which may then be cleared immediately when the +VCPU returns from the call. + +References +========== + +.. [atomic-ops] Documentation/core-api/atomic_ops.rst +.. [memory-barriers] Documentation/memory-barriers.txt +.. [lwn-mb] https://lwn.net/Articles/573436/ diff --git a/Documentation/virt/paravirt_ops.rst b/Documentation/virt/paravirt_ops.rst new file mode 100644 index 000000000000..6b789d27cead --- /dev/null +++ b/Documentation/virt/paravirt_ops.rst @@ -0,0 +1,35 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============ +Paravirt_ops +============ + +Linux provides support for different hypervisor virtualization technologies. +Historically different binary kernels would be required in order to support +different hypervisors, this restriction was removed with pv_ops. +Linux pv_ops is a virtualization API which enables support for different +hypervisors. It allows each hypervisor to override critical operations and +allows a single kernel binary to run on all supported execution environments +including native machine -- without any hypervisors. + +pv_ops provides a set of function pointers which represent operations +corresponding to low level critical instructions and high level +functionalities in various areas. pv-ops allows for optimizations at run +time by enabling binary patching of the low-ops critical operations +at boot time. + +pv_ops operations are classified into three categories: + +- simple indirect call + These operations correspond to high level functionality where it is + known that the overhead of indirect call isn't very important. + +- indirect call which allows optimization with binary patch + Usually these operations correspond to low level critical instructions. They + are called frequently and are performance critical. The overhead is + very important. + +- a set of macros for hand written assembly code + Hand written assembly codes (.S files) also need paravirtualization + because they include sensitive instructions or some of code paths in + them are very performance critical. diff --git a/Documentation/virt/uml/UserModeLinux-HOWTO.txt b/Documentation/virt/uml/UserModeLinux-HOWTO.txt new file mode 100644 index 000000000000..87b80f589e1c --- /dev/null +++ b/Documentation/virt/uml/UserModeLinux-HOWTO.txt @@ -0,0 +1,4589 @@ + User Mode Linux HOWTO + User Mode Linux Core Team + Mon Nov 18 14:16:16 EST 2002 + + This document describes the use and abuse of Jeff Dike's User Mode + Linux: a port of the Linux kernel as a normal Intel Linux process. + ______________________________________________________________________ + + Table of Contents + + 1. Introduction + + 1.1 How is User Mode Linux Different? + 1.2 Why Would I Want User Mode Linux? + + 2. Compiling the kernel and modules + + 2.1 Compiling the kernel + 2.2 Compiling and installing kernel modules + 2.3 Compiling and installing uml_utilities + + 3. Running UML and logging in + + 3.1 Running UML + 3.2 Logging in + 3.3 Examples + + 4. UML on 2G/2G hosts + + 4.1 Introduction + 4.2 The problem + 4.3 The solution + + 5. Setting up serial lines and consoles + + 5.1 Specifying the device + 5.2 Specifying the channel + 5.3 Examples + + 6. Setting up the network + + 6.1 General setup + 6.2 Userspace daemons + 6.3 Specifying ethernet addresses + 6.4 UML interface setup + 6.5 Multicast + 6.6 TUN/TAP with the uml_net helper + 6.7 TUN/TAP with a preconfigured tap device + 6.8 Ethertap + 6.9 The switch daemon + 6.10 Slip + 6.11 Slirp + 6.12 pcap + 6.13 Setting up the host yourself + + 7. Sharing Filesystems between Virtual Machines + + 7.1 A warning + 7.2 Using layered block devices + 7.3 Note! + 7.4 Another warning + 7.5 uml_moo : Merging a COW file with its backing file + + 8. Creating filesystems + + 8.1 Create the filesystem file + 8.2 Assign the file to a UML device + 8.3 Creating and mounting the filesystem + + 9. Host file access + + 9.1 Using hostfs + 9.2 hostfs as the root filesystem + 9.3 Building hostfs + + 10. The Management Console + 10.1 version + 10.2 halt and reboot + 10.3 config + 10.4 remove + 10.5 sysrq + 10.6 help + 10.7 cad + 10.8 stop + 10.9 go + + 11. Kernel debugging + + 11.1 Starting the kernel under gdb + 11.2 Examining sleeping processes + 11.3 Running ddd on UML + 11.4 Debugging modules + 11.5 Attaching gdb to the kernel + 11.6 Using alternate debuggers + + 12. Kernel debugging examples + + 12.1 The case of the hung fsck + 12.2 Episode 2: The case of the hung fsck + + 13. What to do when UML doesn't work + + 13.1 Strange compilation errors when you build from source + 13.2 (obsolete) + 13.3 A variety of panics and hangs with /tmp on a reiserfs filesystem + 13.4 The compile fails with errors about conflicting types for 'open', 'dup', and 'waitpid' + 13.5 UML doesn't work when /tmp is an NFS filesystem + 13.6 UML hangs on boot when compiled with gprof support + 13.7 syslogd dies with a SIGTERM on startup + 13.8 TUN/TAP networking doesn't work on a 2.4 host + 13.9 You can network to the host but not to other machines on the net + 13.10 I have no root and I want to scream + 13.11 UML build conflict between ptrace.h and ucontext.h + 13.12 The UML BogoMips is exactly half the host's BogoMips + 13.13 When you run UML, it immediately segfaults + 13.14 xterms appear, then immediately disappear + 13.15 Any other panic, hang, or strange behavior + + 14. Diagnosing Problems + + 14.1 Case 1 : Normal kernel panics + 14.2 Case 2 : Tracing thread panics + 14.3 Case 3 : Tracing thread panics caused by other threads + 14.4 Case 4 : Hangs + + 15. Thanks + + 15.1 Code and Documentation + 15.2 Flushing out bugs + 15.3 Buglets and clean-ups + 15.4 Case Studies + 15.5 Other contributions + + + ______________________________________________________________________ + + 1. Introduction + + Welcome to User Mode Linux. It's going to be fun. + + + + 1.1. How is User Mode Linux Different? + + Normally, the Linux Kernel talks straight to your hardware (video + card, keyboard, hard drives, etc), and any programs which run ask the + kernel to operate the hardware, like so: + + + + +-----------+-----------+----+ + | Process 1 | Process 2 | ...| + +-----------+-----------+----+ + | Linux Kernel | + +----------------------------+ + | Hardware | + +----------------------------+ + + + + + The User Mode Linux Kernel is different; instead of talking to the + hardware, it talks to a `real' Linux kernel (called the `host kernel' + from now on), like any other program. Programs can then run inside + User-Mode Linux as if they were running under a normal kernel, like + so: + + + + +----------------+ + | Process 2 | ...| + +-----------+----------------+ + | Process 1 | User-Mode Linux| + +----------------------------+ + | Linux Kernel | + +----------------------------+ + | Hardware | + +----------------------------+ + + + + + + 1.2. Why Would I Want User Mode Linux? + + + 1. If User Mode Linux crashes, your host kernel is still fine. + + 2. You can run a usermode kernel as a non-root user. + + 3. You can debug the User Mode Linux like any normal process. + + 4. You can run gprof (profiling) and gcov (coverage testing). + + 5. You can play with your kernel without breaking things. + + 6. You can use it as a sandbox for testing new apps. + + 7. You can try new development kernels safely. + + 8. You can run different distributions simultaneously. + + 9. It's extremely fun. + + + + + + 2. Compiling the kernel and modules + + + + + 2.1. Compiling the kernel + + + Compiling the user mode kernel is just like compiling any other + kernel. Let's go through the steps, using 2.4.0-prerelease (current + as of this writing) as an example: + + + 1. Download the latest UML patch from + + the download page <http://user-mode-linux.sourceforge.net/ + + In this example, the file is uml-patch-2.4.0-prerelease.bz2. + + + 2. Download the matching kernel from your favourite kernel mirror, + such as: + + ftp://ftp.ca.kernel.org/pub/kernel/v2.4/linux-2.4.0-prerelease.tar.bz2 + <ftp://ftp.ca.kernel.org/pub/kernel/v2.4/linux-2.4.0-prerelease.tar.bz2> + . + + + 3. Make a directory and unpack the kernel into it. + + + + host% + mkdir ~/uml + + + + + + + host% + cd ~/uml + + + + + + + host% + tar -xzvf linux-2.4.0-prerelease.tar.bz2 + + + + + + + 4. Apply the patch using + + + + host% + cd ~/uml/linux + + + + host% + bzcat uml-patch-2.4.0-prerelease.bz2 | patch -p1 + + + + + + + 5. Run your favorite config; `make xconfig ARCH=um' is the most + convenient. `make config ARCH=um' and 'make menuconfig ARCH=um' + will work as well. The defaults will give you a useful kernel. If + you want to change something, go ahead, it probably won't hurt + anything. + + + Note: If the host is configured with a 2G/2G address space split + rather than the usual 3G/1G split, then the packaged UML binaries + will not run. They will immediately segfault. See ``UML on 2G/2G + hosts'' for the scoop on running UML on your system. + + + + 6. Finish with `make linux ARCH=um': the result is a file called + `linux' in the top directory of your source tree. + + Make sure that you don't build this kernel in /usr/src/linux. On some + distributions, /usr/include/asm is a link into this pool. The user- + mode build changes the other end of that link, and things that include + <asm/anything.h> stop compiling. + + The sources are also available from cvs at the project's cvs page, + which has directions on getting the sources. You can also browse the + CVS pool from there. + + If you get the CVS sources, you will have to check them out into an + empty directory. You will then have to copy each file into the + corresponding directory in the appropriate kernel pool. + + If you don't have the latest kernel pool, you can get the + corresponding user-mode sources with + + + host% cvs co -r v_2_3_x linux + + + + + where 'x' is the version in your pool. Note that you will not get the + bug fixes and enhancements that have gone into subsequent releases. + + + 2.2. Compiling and installing kernel modules + + UML modules are built in the same way as the native kernel (with the + exception of the 'ARCH=um' that you always need for UML): + + + host% make modules ARCH=um + + + + + Any modules that you want to load into this kernel need to be built in + the user-mode pool. Modules from the native kernel won't work. + + You can install them by using ftp or something to copy them into the + virtual machine and dropping them into /lib/modules/`uname -r`. + + You can also get the kernel build process to install them as follows: + + 1. with the kernel not booted, mount the root filesystem in the top + level of the kernel pool: + + + host% mount root_fs mnt -o loop + + + + + + + 2. run + + + host% + make modules_install INSTALL_MOD_PATH=`pwd`/mnt ARCH=um + + + + + + + 3. unmount the filesystem + + + host% umount mnt + + + + + + + 4. boot the kernel on it + + + When the system is booted, you can use insmod as usual to get the + modules into the kernel. A number of things have been loaded into UML + as modules, especially filesystems and network protocols and filters, + so most symbols which need to be exported probably already are. + However, if you do find symbols that need exporting, let us + <http://user-mode-linux.sourceforge.net/> know, and + they'll be "taken care of". + + + + 2.3. Compiling and installing uml_utilities + + Many features of the UML kernel require a user-space helper program, + so a uml_utilities package is distributed separately from the kernel + patch which provides these helpers. Included within this is: + + o port-helper - Used by consoles which connect to xterms or ports + + o tunctl - Configuration tool to create and delete tap devices + + o uml_net - Setuid binary for automatic tap device configuration + + o uml_switch - User-space virtual switch required for daemon + transport + + The uml_utilities tree is compiled with: + + + host# + make && make install + + + + + Note that UML kernel patches may require a specific version of the + uml_utilities distribution. If you don't keep up with the mailing + lists, ensure that you have the latest release of uml_utilities if you + are experiencing problems with your UML kernel, particularly when + dealing with consoles or command-line switches to the helper programs + + + + + + + + + 3. Running UML and logging in + + + + 3.1. Running UML + + It runs on 2.2.15 or later, and all 2.4 kernels. + + + Booting UML is straightforward. Simply run 'linux': it will try to + mount the file `root_fs' in the current directory. You do not need to + run it as root. If your root filesystem is not named `root_fs', then + you need to put a `ubd0=root_fs_whatever' switch on the linux command + line. + + + You will need a filesystem to boot UML from. There are a number + available for download from here <http://user-mode- + linux.sourceforge.net/> . There are also several tools + <http://user-mode-linux.sourceforge.net/> which can be + used to generate UML-compatible filesystem images from media. + The kernel will boot up and present you with a login prompt. + + + Note: If the host is configured with a 2G/2G address space split + rather than the usual 3G/1G split, then the packaged UML binaries will + not run. They will immediately segfault. See ``UML on 2G/2G hosts'' + for the scoop on running UML on your system. + + + + 3.2. Logging in + + + + The prepackaged filesystems have a root account with password 'root' + and a user account with password 'user'. The login banner will + generally tell you how to log in. So, you log in and you will find + yourself inside a little virtual machine. Our filesystems have a + variety of commands and utilities installed (and it is fairly easy to + add more), so you will have a lot of tools with which to poke around + the system. + + There are a couple of other ways to log in: + + o On a virtual console + + + + Each virtual console that is configured (i.e. the device exists in + /dev and /etc/inittab runs a getty on it) will come up in its own + xterm. If you get tired of the xterms, read ``Setting up serial + lines and consoles'' to see how to attach the consoles to + something else, like host ptys. + + + + o Over the serial line + + + In the boot output, find a line that looks like: + + + + serial line 0 assigned pty /dev/ptyp1 + + + + + Attach your favorite terminal program to the corresponding tty. I.e. + for minicom, the command would be + + + host% minicom -o -p /dev/ttyp1 + + + + + + + o Over the net + + + If the network is running, then you can telnet to the virtual + machine and log in to it. See ``Setting up the network'' to learn + about setting up a virtual network. + + When you're done using it, run halt, and the kernel will bring itself + down and the process will exit. + + + 3.3. Examples + + Here are some examples of UML in action: + + o A login session <http://user-mode-linux.sourceforge.net/login.html> + + o A virtual network <http://user-mode-linux.sourceforge.net/net.html> + + + + + + + + 4. UML on 2G/2G hosts + + + + + 4.1. Introduction + + + Most Linux machines are configured so that the kernel occupies the + upper 1G (0xc0000000 - 0xffffffff) of the 4G address space and + processes use the lower 3G (0x00000000 - 0xbfffffff). However, some + machine are configured with a 2G/2G split, with the kernel occupying + the upper 2G (0x80000000 - 0xffffffff) and processes using the lower + 2G (0x00000000 - 0x7fffffff). + + + + + 4.2. The problem + + + The prebuilt UML binaries on this site will not run on 2G/2G hosts + because UML occupies the upper .5G of the 3G process address space + (0xa0000000 - 0xbfffffff). Obviously, on 2G/2G hosts, this is right + in the middle of the kernel address space, so UML won't even load - it + will immediately segfault. + + + + + 4.3. The solution + + + The fix for this is to rebuild UML from source after enabling + CONFIG_HOST_2G_2G (under 'General Setup'). This will cause UML to + load itself in the top .5G of that smaller process address space, + where it will run fine. See ``Compiling the kernel and modules'' if + you need help building UML from source. + + + + + + + + + + + 5. Setting up serial lines and consoles + + + It is possible to attach UML serial lines and consoles to many types + of host I/O channels by specifying them on the command line. + + + You can attach them to host ptys, ttys, file descriptors, and ports. + This allows you to do things like + + o have a UML console appear on an unused host console, + + o hook two virtual machines together by having one attach to a pty + and having the other attach to the corresponding tty + + o make a virtual machine accessible from the net by attaching a + console to a port on the host. + + + The general format of the command line option is device=channel. + + + + 5.1. Specifying the device + + Devices are specified with "con" or "ssl" (console or serial line, + respectively), optionally with a device number if you are talking + about a specific device. + + + Using just "con" or "ssl" describes all of the consoles or serial + lines. If you want to talk about console #3 or serial line #10, they + would be "con3" and "ssl10", respectively. + + + A specific device name will override a less general "con=" or "ssl=". + So, for example, you can assign a pty to each of the serial lines + except for the first two like this: + + + ssl=pty ssl0=tty:/dev/tty0 ssl1=tty:/dev/tty1 + + + + + The specificity of the device name is all that matters; order on the + command line is irrelevant. + + + + 5.2. Specifying the channel + + There are a number of different types of channels to attach a UML + device to, each with a different way of specifying exactly what to + attach to. + + o pseudo-terminals - device=pty pts terminals - device=pts + + + This will cause UML to allocate a free host pseudo-terminal for the + device. The terminal that it got will be announced in the boot + log. You access it by attaching a terminal program to the + corresponding tty: + + o screen /dev/pts/n + + o screen /dev/ttyxx + + o minicom -o -p /dev/ttyxx - minicom seems not able to handle pts + devices + + o kermit - start it up, 'open' the device, then 'connect' + + + + + + o terminals - device=tty:tty device file + + + This will make UML attach the device to the specified tty (i.e + + + con1=tty:/dev/tty3 + + + + + will attach UML's console 1 to the host's /dev/tty3). If the tty that + you specify is the slave end of a tty/pty pair, something else must + have already opened the corresponding pty in order for this to work. + + + + + + o xterms - device=xterm + + + UML will run an xterm and the device will be attached to it. + + + + + + o Port - device=port:port number + + + This will attach the UML devices to the specified host port. + Attaching console 1 to the host's port 9000 would be done like + this: + + + con1=port:9000 + + + + + Attaching all the serial lines to that port would be done similarly: + + + ssl=port:9000 + + + + + You access these devices by telnetting to that port. Each active tel- + net session gets a different device. If there are more telnets to a + port than UML devices attached to it, then the extra telnet sessions + will block until an existing telnet detaches, or until another device + becomes active (i.e. by being activated in /etc/inittab). + + This channel has the advantage that you can both attach multiple UML + devices to it and know how to access them without reading the UML boot + log. It is also unique in allowing access to a UML from remote + machines without requiring that the UML be networked. This could be + useful in allowing public access to UMLs because they would be + accessible from the net, but wouldn't need any kind of network + filtering or access control because they would have no network access. + + + If you attach the main console to a portal, then the UML boot will + appear to hang. In reality, it's waiting for a telnet to connect, at + which point the boot will proceed. + + + + + + o already-existing file descriptors - device=file descriptor + + + If you set up a file descriptor on the UML command line, you can + attach a UML device to it. This is most commonly used to put the + main console back on stdin and stdout after assigning all the other + consoles to something else: + + + con0=fd:0,fd:1 con=pts + + + + + + + + + o Nothing - device=null + + + This allows the device to be opened, in contrast to 'none', but + reads will block, and writes will succeed and the data will be + thrown out. + + + + + + o None - device=none + + + This causes the device to disappear. + + + + You can also specify different input and output channels for a device + by putting a comma between them: + + + ssl3=tty:/dev/tty2,xterm + + + + + will cause serial line 3 to accept input on the host's /dev/tty2 and + display output on an xterm. That's a silly example - the most common + use of this syntax is to reattach the main console to stdin and stdout + as shown above. + + + If you decide to move the main console away from stdin/stdout, the + initial boot output will appear in the terminal that you're running + UML in. However, once the console driver has been officially + initialized, then the boot output will start appearing wherever you + specified that console 0 should be. That device will receive all + subsequent output. + + + + 5.3. Examples + + There are a number of interesting things you can do with this + capability. + + + First, this is how you get rid of those bleeding console xterms by + attaching them to host ptys: + + + con=pty con0=fd:0,fd:1 + + + + + This will make a UML console take over an unused host virtual console, + so that when you switch to it, you will see the UML login prompt + rather than the host login prompt: + + + con1=tty:/dev/tty6 + + + + + You can attach two virtual machines together with what amounts to a + serial line as follows: + + Run one UML with a serial line attached to a pty - + + + ssl1=pty + + + + + Look at the boot log to see what pty it got (this example will assume + that it got /dev/ptyp1). + + Boot the other UML with a serial line attached to the corresponding + tty - + + + ssl1=tty:/dev/ttyp1 + + + + + Log in, make sure that it has no getty on that serial line, attach a + terminal program like minicom to it, and you should see the login + prompt of the other virtual machine. + + + 6. Setting up the network + + + + This page describes how to set up the various transports and to + provide a UML instance with network access to the host, other machines + on the local net, and the rest of the net. + + + As of 2.4.5, UML networking has been completely redone to make it much + easier to set up, fix bugs, and add new features. + + + There is a new helper, uml_net, which does the host setup that + requires root privileges. + + + There are currently five transport types available for a UML virtual + machine to exchange packets with other hosts: + + o ethertap + + o TUN/TAP + + o Multicast + + o a switch daemon + + o slip + + o slirp + + o pcap + + The TUN/TAP, ethertap, slip, and slirp transports allow a UML + instance to exchange packets with the host. They may be directed + to the host or the host may just act as a router to provide access + to other physical or virtual machines. + + + The pcap transport is a synthetic read-only interface, using the + libpcap binary to collect packets from interfaces on the host and + filter them. This is useful for building preconfigured traffic + monitors or sniffers. + + + The daemon and multicast transports provide a completely virtual + network to other virtual machines. This network is completely + disconnected from the physical network unless one of the virtual + machines on it is acting as a gateway. + + + With so many host transports, which one should you use? Here's when + you should use each one: + + o ethertap - if you want access to the host networking and it is + running 2.2 + + o TUN/TAP - if you want access to the host networking and it is + running 2.4. Also, the TUN/TAP transport is able to use a + preconfigured device, allowing it to avoid using the setuid uml_net + helper, which is a security advantage. + + o Multicast - if you want a purely virtual network and you don't want + to set up anything but the UML + + o a switch daemon - if you want a purely virtual network and you + don't mind running the daemon in order to get somewhat better + performance + + o slip - there is no particular reason to run the slip backend unless + ethertap and TUN/TAP are just not available for some reason + + o slirp - if you don't have root access on the host to setup + networking, or if you don't want to allocate an IP to your UML + + o pcap - not much use for actual network connectivity, but great for + monitoring traffic on the host + + Ethertap is available on 2.4 and works fine. TUN/TAP is preferred + to it because it has better performance and ethertap is officially + considered obsolete in 2.4. Also, the root helper only needs to + run occasionally for TUN/TAP, rather than handling every packet, as + it does with ethertap. This is a slight security advantage since + it provides fewer opportunities for a nasty UML user to somehow + exploit the helper's root privileges. + + + 6.1. General setup + + First, you must have the virtual network enabled in your UML. If are + running a prebuilt kernel from this site, everything is already + enabled. If you build the kernel yourself, under the "Network device + support" menu, enable "Network device support", and then the three + transports. + + + The next step is to provide a network device to the virtual machine. + This is done by describing it on the kernel command line. + + The general format is + + + eth <n> = <transport> , <transport args> + + + + + For example, a virtual ethernet device may be attached to a host + ethertap device as follows: + + + eth0=ethertap,tap0,fe:fd:0:0:0:1,192.168.0.254 + + + + + This sets up eth0 inside the virtual machine to attach itself to the + host /dev/tap0, assigns it an ethernet address, and assigns the host + tap0 interface an IP address. + + + + Note that the IP address you assign to the host end of the tap device + must be different than the IP you assign to the eth device inside UML. + If you are short on IPs and don't want to consume two per UML, then + you can reuse the host's eth IP address for the host ends of the tap + devices. Internally, the UMLs must still get unique IPs for their eth + devices. You can also give the UMLs non-routable IPs (192.168.x.x or + 10.x.x.x) and have the host masquerade them. This will let outgoing + connections work, but incoming connections won't without more work, + such as port forwarding from the host. + Also note that when you configure the host side of an interface, it is + only acting as a gateway. It will respond to pings sent to it + locally, but is not useful to do that since it's a host interface. + You are not talking to the UML when you ping that interface and get a + response. + + + You can also add devices to a UML and remove them at runtime. See the + ``The Management Console'' page for details. + + + The sections below describe this in more detail. + + + Once you've decided how you're going to set up the devices, you boot + UML, log in, configure the UML side of the devices, and set up routes + to the outside world. At that point, you will be able to talk to any + other machines, physical or virtual, on the net. + + + If ifconfig inside UML fails and the network refuses to come up, run + tell you what went wrong. + + + + 6.2. Userspace daemons + + You will likely need the setuid helper, or the switch daemon, or both. + They are both installed with the RPM and deb, so if you've installed + either, you can skip the rest of this section. + + + If not, then you need to check them out of CVS, build them, and + install them. The helper is uml_net, in CVS /tools/uml_net, and the + daemon is uml_switch, in CVS /tools/uml_router. They are both built + with a plain 'make'. Both need to be installed in a directory that's + in your path - /usr/bin is recommend. On top of that, uml_net needs + to be setuid root. + + + + 6.3. Specifying ethernet addresses + + Below, you will see that the TUN/TAP, ethertap, and daemon interfaces + allow you to specify hardware addresses for the virtual ethernet + devices. This is generally not necessary. If you don't have a + specific reason to do it, you probably shouldn't. If one is not + specified on the command line, the driver will assign one based on the + device IP address. It will provide the address fe:fd:nn:nn:nn:nn + where nn.nn.nn.nn is the device IP address. This is nearly always + sufficient to guarantee a unique hardware address for the device. A + couple of exceptions are: + + o Another set of virtual ethernet devices are on the same network and + they are assigned hardware addresses using a different scheme which + may conflict with the UML IP address-based scheme + + o You aren't going to use the device for IP networking, so you don't + assign the device an IP address + + If you let the driver provide the hardware address, you should make + sure that the device IP address is known before the interface is + brought up. So, inside UML, this will guarantee that: + + + + UML# + ifconfig eth0 192.168.0.250 up + + + + + If you decide to assign the hardware address yourself, make sure that + the first byte of the address is even. Addresses with an odd first + byte are broadcast addresses, which you don't want assigned to a + device. + + + + 6.4. UML interface setup + + Once the network devices have been described on the command line, you + should boot UML and log in. + + + The first thing to do is bring the interface up: + + + UML# ifconfig ethn ip-address up + + + + + You should be able to ping the host at this point. + + + To reach the rest of the world, you should set a default route to the + host: + + + UML# route add default gw host ip + + + + + Again, with host ip of 192.168.0.4: + + + UML# route add default gw 192.168.0.4 + + + + + This page used to recommend setting a network route to your local net. + This is wrong, because it will cause UML to try to figure out hardware + addresses of the local machines by arping on the interface to the + host. Since that interface is basically a single strand of ethernet + with two nodes on it (UML and the host) and arp requests don't cross + networks, they will fail to elicit any responses. So, what you want + is for UML to just blindly throw all packets at the host and let it + figure out what to do with them, which is what leaving out the network + route and adding the default route does. + + + Note: If you can't communicate with other hosts on your physical + ethernet, it's probably because of a network route that's + automatically set up. If you run 'route -n' and see a route that + looks like this: + + + + + Destination Gateway Genmask Flags Metric Ref Use Iface + 192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 + + + + + with a mask that's not 255.255.255.255, then replace it with a route + to your host: + + + UML# + route del -net 192.168.0.0 dev eth0 netmask 255.255.255.0 + + + + + + + UML# + route add -host 192.168.0.4 dev eth0 + + + + + This, plus the default route to the host, will allow UML to exchange + packets with any machine on your ethernet. + + + + 6.5. Multicast + + The simplest way to set up a virtual network between multiple UMLs is + to use the mcast transport. This was written by Harald Welte and is + present in UML version 2.4.5-5um and later. Your system must have + multicast enabled in the kernel and there must be a multicast-capable + network device on the host. Normally, this is eth0, but if there is + no ethernet card on the host, then you will likely get strange error + messages when you bring the device up inside UML. + + + To use it, run two UMLs with + + + eth0=mcast + + + + + on their command lines. Log in, configure the ethernet device in each + machine with different IP addresses: + + + UML1# ifconfig eth0 192.168.0.254 + + + + + + + UML2# ifconfig eth0 192.168.0.253 + + + + + and they should be able to talk to each other. + + The full set of command line options for this transport are + + + + ethn=mcast,ethernet address,multicast + address,multicast port,ttl + + + + + Harald's original README is here <http://user-mode-linux.source- + forge.net/> and explains these in detail, as well as + some other issues. + + There is also a related point-to-point only "ucast" transport. + This is useful when your network does not support multicast, and + all network connections are simple point to point links. + + The full set of command line options for this transport are + + + ethn=ucast,ethernet address,remote address,listen port,remote port + + + + + 6.6. TUN/TAP with the uml_net helper + + TUN/TAP is the preferred mechanism on 2.4 to exchange packets with the + host. The TUN/TAP backend has been in UML since 2.4.9-3um. + + + The easiest way to get up and running is to let the setuid uml_net + helper do the host setup for you. This involves insmod-ing the tun.o + module if necessary, configuring the device, and setting up IP + forwarding, routing, and proxy arp. If you are new to UML networking, + do this first. If you're concerned about the security implications of + the setuid helper, use it to get up and running, then read the next + section to see how to have UML use a preconfigured tap device, which + avoids the use of uml_net. + + + If you specify an IP address for the host side of the device, the + uml_net helper will do all necessary setup on the host - the only + requirement is that TUN/TAP be available, either built in to the host + kernel or as the tun.o module. + + The format of the command line switch to attach a device to a TUN/TAP + device is + + + eth <n> =tuntap,,, <IP address> + + + + + For example, this argument will attach the UML's eth0 to the next + available tap device and assign an ethernet address to it based on its + IP address + + + eth0=tuntap,,,192.168.0.254 + + + + + + + Note that the IP address that must be used for the eth device inside + UML is fixed by the routing and proxy arp that is set up on the + TUN/TAP device on the host. You can use a different one, but it won't + work because reply packets won't reach the UML. This is a feature. + It prevents a nasty UML user from doing things like setting the UML IP + to the same as the network's nameserver or mail server. + + + There are a couple potential problems with running the TUN/TAP + transport on a 2.4 host kernel + + o TUN/TAP seems not to work on 2.4.3 and earlier. Upgrade the host + kernel or use the ethertap transport. + + o With an upgraded kernel, TUN/TAP may fail with + + + File descriptor in bad state + + + + + This is due to a header mismatch between the upgraded kernel and the + kernel that was originally installed on the machine. The fix is to + make sure that /usr/src/linux points to the headers for the running + kernel. + + These were pointed out by Tim Robinson <timro at trkr dot net> in + <http://www.geocrawler.com/> name="this uml- + user post"> . + + + + 6.7. TUN/TAP with a preconfigured tap device + + If you prefer not to have UML use uml_net (which is somewhat + insecure), with UML 2.4.17-11, you can set up a TUN/TAP device + beforehand. The setup needs to be done as root, but once that's done, + there is no need for root assistance. Setting up the device is done + as follows: + + o Create the device with tunctl (available from the UML utilities + tarball) + + + + + host# tunctl -u uid + + + + + where uid is the user id or username that UML will be run as. This + will tell you what device was created. + + o Configure the device IP (change IP addresses and device name to + suit) + + + + + host# ifconfig tap0 192.168.0.254 up + + + + + + o Set up routing and arping if desired - this is my recipe, there are + other ways of doing the same thing + + + host# + bash -c 'echo 1 > /proc/sys/net/ipv4/ip_forward' + + host# + route add -host 192.168.0.253 dev tap0 + + + + + + + host# + bash -c 'echo 1 > /proc/sys/net/ipv4/conf/tap0/proxy_arp' + + + + + + + host# + arp -Ds 192.168.0.253 eth0 pub + + + + + Note that this must be done every time the host boots - this configu- + ration is not stored across host reboots. So, it's probably a good + idea to stick it in an rc file. An even better idea would be a little + utility which reads the information from a config file and sets up + devices at boot time. + + o Rather than using up two IPs and ARPing for one of them, you can + also provide direct access to your LAN by the UML by using a + bridge. + + + host# + brctl addbr br0 + + + + + + + host# + ifconfig eth0 0.0.0.0 promisc up + + + + + + + host# + ifconfig tap0 0.0.0.0 promisc up + + + + + + + host# + ifconfig br0 192.168.0.1 netmask 255.255.255.0 up + + + + + + + + host# + brctl stp br0 off + + + + + + + host# + brctl setfd br0 1 + + + + + + + host# + brctl sethello br0 1 + + + + + + + host# + brctl addif br0 eth0 + + + + + + + host# + brctl addif br0 tap0 + + + + + Note that 'br0' should be setup using ifconfig with the existing IP + address of eth0, as eth0 no longer has its own IP. + + o + + + Also, the /dev/net/tun device must be writable by the user running + UML in order for the UML to use the device that's been configured + for it. The simplest thing to do is + + + host# chmod 666 /dev/net/tun + + + + + Making it world-writable looks bad, but it seems not to be + exploitable as a security hole. However, it does allow anyone to cre- + ate useless tap devices (useless because they can't configure them), + which is a DOS attack. A somewhat more secure alternative would to be + to create a group containing all the users who have preconfigured tap + devices and chgrp /dev/net/tun to that group with mode 664 or 660. + + + o Once the device is set up, run UML with 'eth0=tuntap,device name' + (i.e. 'eth0=tuntap,tap0') on the command line (or do it with the + mconsole config command). + + o Bring the eth device up in UML and you're in business. + + If you don't want that tap device any more, you can make it non- + persistent with + + + host# tunctl -d tap device + + + + + Finally, tunctl has a -b (for brief mode) switch which causes it to + output only the name of the tap device it created. This makes it + suitable for capture by a script: + + + host# TAP=`tunctl -u 1000 -b` + + + + + + + 6.8. Ethertap + + Ethertap is the general mechanism on 2.2 for userspace processes to + exchange packets with the kernel. + + + + To use this transport, you need to describe the virtual network device + on the UML command line. The general format for this is + + + eth <n> =ethertap, <device> , <ethernet address> , <tap IP address> + + + + + So, the previous example + + + eth0=ethertap,tap0,fe:fd:0:0:0:1,192.168.0.254 + + + + + attaches the UML eth0 device to the host /dev/tap0, assigns it the + ethernet address fe:fd:0:0:0:1, and assigns the IP address + 192.168.0.254 to the tap device. + + + + The tap device is mandatory, but the others are optional. If the + ethernet address is omitted, one will be assigned to it. + + + The presence of the tap IP address will cause the helper to run and do + whatever host setup is needed to allow the virtual machine to + communicate with the outside world. If you're not sure you know what + you're doing, this is the way to go. + + + If it is absent, then you must configure the tap device and whatever + arping and routing you will need on the host. However, even in this + case, the uml_net helper still needs to be in your path and it must be + setuid root if you're not running UML as root. This is because the + tap device doesn't support SIGIO, which UML needs in order to use + something as a source of input. So, the helper is used as a + convenient asynchronous IO thread. + + If you're using the uml_net helper, you can ignore the following host + setup - uml_net will do it for you. You just need to make sure you + have ethertap available, either built in to the host kernel or + available as a module. + + + If you want to set things up yourself, you need to make sure that the + appropriate /dev entry exists. If it doesn't, become root and create + it as follows: + + + mknod /dev/tap <minor> c 36 <minor> + 16 + + + + + For example, this is how to create /dev/tap0: + + + mknod /dev/tap0 c 36 0 + 16 + + + + + You also need to make sure that the host kernel has ethertap support. + If ethertap is enabled as a module, you apparently need to insmod + ethertap once for each ethertap device you want to enable. So, + + + host# + insmod ethertap + + + + + will give you the tap0 interface. To get the tap1 interface, you need + to run + + + host# + insmod ethertap unit=1 -o ethertap1 + + + + + + + + 6.9. The switch daemon + + Note: This is the daemon formerly known as uml_router, but which was + renamed so the network weenies of the world would stop growling at me. + + + The switch daemon, uml_switch, provides a mechanism for creating a + totally virtual network. By default, it provides no connection to the + host network (but see -tap, below). + + + The first thing you need to do is run the daemon. Running it with no + arguments will make it listen on a default pair of unix domain + sockets. + + + If you want it to listen on a different pair of sockets, use + + + -unix control socket data socket + + + + + + If you want it to act as a hub rather than a switch, use + + + -hub + + + + + + If you want the switch to be connected to host networking (allowing + the umls to get access to the outside world through the host), use + + + -tap tap0 + + + + + + Note that the tap device must be preconfigured (see "TUN/TAP with a + preconfigured tap device", above). If you're using a different tap + device than tap0, specify that instead of tap0. + + + uml_switch can be backgrounded as follows + + + host% + uml_switch [ options ] < /dev/null > /dev/null + + + + + The reason it doesn't background by default is that it listens to + stdin for EOF. When it sees that, it exits. + + + The general format of the kernel command line switch is + + + + ethn=daemon,ethernet address,socket + type,control socket,data socket + + + + + You can leave off everything except the 'daemon'. You only need to + specify the ethernet address if the one that will be assigned to it + isn't acceptable for some reason. The rest of the arguments describe + how to communicate with the daemon. You should only specify them if + you told the daemon to use different sockets than the default. So, if + you ran the daemon with no arguments, running the UML on the same + machine with + eth0=daemon + + + + + will cause the eth0 driver to attach itself to the daemon correctly. + + + + 6.10. Slip + + Slip is another, less general, mechanism for a process to communicate + with the host networking. In contrast to the ethertap interface, + which exchanges ethernet frames with the host and can be used to + transport any higher-level protocol, it can only be used to transport + IP. + + + The general format of the command line switch is + + + + ethn=slip,slip IP + + + + + The slip IP argument is the IP address that will be assigned to the + host end of the slip device. If it is specified, the helper will run + and will set up the host so that the virtual machine can reach it and + the rest of the network. + + + There are some oddities with this interface that you should be aware + of. You should only specify one slip device on a given virtual + machine, and its name inside UML will be 'umn', not 'eth0' or whatever + you specified on the command line. These problems will be fixed at + some point. + + + + 6.11. Slirp + + slirp uses an external program, usually /usr/bin/slirp, to provide IP + only networking connectivity through the host. This is similar to IP + masquerading with a firewall, although the translation is performed in + user-space, rather than by the kernel. As slirp does not set up any + interfaces on the host, or changes routing, slirp does not require + root access or setuid binaries on the host. + + + The general format of the command line switch for slirp is: + + + + ethn=slirp,ethernet address,slirp path + + + + + The ethernet address is optional, as UML will set up the interface + with an ethernet address based upon the initial IP address of the + interface. The slirp path is generally /usr/bin/slirp, although it + will depend on distribution. + + + The slirp program can have a number of options passed to the command + line and we can't add them to the UML command line, as they will be + parsed incorrectly. Instead, a wrapper shell script can be written or + the options inserted into the /.slirprc file. More information on + all of the slirp options can be found in its man pages. + + + The eth0 interface on UML should be set up with the IP 10.2.0.15, + although you can use anything as long as it is not used by a network + you will be connecting to. The default route on UML should be set to + use + + + UML# + route add default dev eth0 + + + + + slirp provides a number of useful IP addresses which can be used by + UML, such as 10.0.2.3 which is an alias for the DNS server specified + in /etc/resolv.conf on the host or the IP given in the 'dns' option + for slirp. + + + Even with a baudrate setting higher than 115200, the slirp connection + is limited to 115200. If you need it to go faster, the slirp binary + needs to be compiled with FULL_BOLT defined in config.h. + + + + 6.12. pcap + + The pcap transport is attached to a UML ethernet device on the command + line or with uml_mconsole with the following syntax: + + + + ethn=pcap,host interface,filter + expression,option1,option2 + + + + + The expression and options are optional. + + + The interface is whatever network device on the host you want to + sniff. The expression is a pcap filter expression, which is also what + tcpdump uses, so if you know how to specify tcpdump filters, you will + use the same expressions here. The options are up to two of + 'promisc', control whether pcap puts the host interface into + promiscuous mode. 'optimize' and 'nooptimize' control whether the pcap + expression optimizer is used. + + + Example: + + + + eth0=pcap,eth0,tcp + + eth1=pcap,eth0,!tcp + + + + will cause the UML eth0 to emit all tcp packets on the host eth0 and + the UML eth1 to emit all non-tcp packets on the host eth0. + + + + 6.13. Setting up the host yourself + + If you don't specify an address for the host side of the ethertap or + slip device, UML won't do any setup on the host. So this is what is + needed to get things working (the examples use a host-side IP of + 192.168.0.251 and a UML-side IP of 192.168.0.250 - adjust to suit your + own network): + + o The device needs to be configured with its IP address. Tap devices + are also configured with an mtu of 1484. Slip devices are + configured with a point-to-point address pointing at the UML ip + address. + + + host# ifconfig tap0 arp mtu 1484 192.168.0.251 up + + + + + + + host# + ifconfig sl0 192.168.0.251 pointopoint 192.168.0.250 up + + + + + + o If a tap device is being set up, a route is set to the UML IP. + + + UML# route add -host 192.168.0.250 gw 192.168.0.251 + + + + + + o To allow other hosts on your network to see the virtual machine, + proxy arp is set up for it. + + + host# arp -Ds 192.168.0.250 eth0 pub + + + + + + o Finally, the host is set up to route packets. + + + host# echo 1 > /proc/sys/net/ipv4/ip_forward + + + + + + + + + + + 7. Sharing Filesystems between Virtual Machines + + + + + 7.1. A warning + + Don't attempt to share filesystems simply by booting two UMLs from the + same file. That's the same thing as booting two physical machines + from a shared disk. It will result in filesystem corruption. + + + + 7.2. Using layered block devices + + The way to share a filesystem between two virtual machines is to use + the copy-on-write (COW) layering capability of the ubd block driver. + As of 2.4.6-2um, the driver supports layering a read-write private + device over a read-only shared device. A machine's writes are stored + in the private device, while reads come from either device - the + private one if the requested block is valid in it, the shared one if + not. Using this scheme, the majority of data which is unchanged is + shared between an arbitrary number of virtual machines, each of which + has a much smaller file containing the changes that it has made. With + a large number of UMLs booting from a large root filesystem, this + leads to a huge disk space saving. It will also help performance, + since the host will be able to cache the shared data using a much + smaller amount of memory, so UML disk requests will be served from the + host's memory rather than its disks. + + + + + To add a copy-on-write layer to an existing block device file, simply + add the name of the COW file to the appropriate ubd switch: + + + ubd0=root_fs_cow,root_fs_debian_22 + + + + + where 'root_fs_cow' is the private COW file and 'root_fs_debian_22' is + the existing shared filesystem. The COW file need not exist. If it + doesn't, the driver will create and initialize it. Once the COW file + has been initialized, it can be used on its own on the command line: + + + ubd0=root_fs_cow + + + + + The name of the backing file is stored in the COW file header, so it + would be redundant to continue specifying it on the command line. + + + + 7.3. Note! + + When checking the size of the COW file in order to see the gobs of + space that you're saving, make sure you use 'ls -ls' to see the actual + disk consumption rather than the length of the file. The COW file is + sparse, so the length will be very different from the disk usage. + Here is a 'ls -l' of a COW file and backing file from one boot and + shutdown: + host% ls -l cow.debian debian2.2 + -rw-r--r-- 1 jdike jdike 492504064 Aug 6 21:16 cow.debian + -rwxrw-rw- 1 jdike jdike 537919488 Aug 6 20:42 debian2.2 + + + + + Doesn't look like much saved space, does it? Well, here's 'ls -ls': + + + host% ls -ls cow.debian debian2.2 + 880 -rw-r--r-- 1 jdike jdike 492504064 Aug 6 21:16 cow.debian + 525832 -rwxrw-rw- 1 jdike jdike 537919488 Aug 6 20:42 debian2.2 + + + + + Now, you can see that the COW file has less than a meg of disk, rather + than 492 meg. + + + + 7.4. Another warning + + Once a filesystem is being used as a readonly backing file for a COW + file, do not boot directly from it or modify it in any way. Doing so + will invalidate any COW files that are using it. The mtime and size + of the backing file are stored in the COW file header at its creation, + and they must continue to match. If they don't, the driver will + refuse to use the COW file. + + + + + If you attempt to evade this restriction by changing either the + backing file or the COW header by hand, you will get a corrupted + filesystem. + + + + + Among other things, this means that upgrading the distribution in a + backing file and expecting that all of the COW files using it will see + the upgrade will not work. + + + + + 7.5. uml_moo : Merging a COW file with its backing file + + Depending on how you use UML and COW devices, it may be advisable to + merge the changes in the COW file into the backing file every once in + a while. + + + + + The utility that does this is uml_moo. Its usage is + + + host% uml_moo COW file new backing file + + + + + There's no need to specify the backing file since that information is + already in the COW file header. If you're paranoid, boot the new + merged file, and if you're happy with it, move it over the old backing + file. + + + + + uml_moo creates a new backing file by default as a safety measure. It + also has a destructive merge option which will merge the COW file + directly into its current backing file. This is really only usable + when the backing file only has one COW file associated with it. If + there are multiple COWs associated with a backing file, a -d merge of + one of them will invalidate all of the others. However, it is + convenient if you're short of disk space, and it should also be + noticeably faster than a non-destructive merge. + + + + + uml_moo is installed with the UML deb and RPM. If you didn't install + UML from one of those packages, you can also get it from the UML + utilities <http://user-mode-linux.sourceforge.net/ + utilities> tar file in tools/moo. + + + + + + + + + 8. Creating filesystems + + + You may want to create and mount new UML filesystems, either because + your root filesystem isn't large enough or because you want to use a + filesystem other than ext2. + + + This was written on the occasion of reiserfs being included in the + 2.4.1 kernel pool, and therefore the 2.4.1 UML, so the examples will + talk about reiserfs. This information is generic, and the examples + should be easy to translate to the filesystem of your choice. + + + 8.1. Create the filesystem file + + dd is your friend. All you need to do is tell dd to create an empty + file of the appropriate size. I usually make it sparse to save time + and to avoid allocating disk space until it's actually used. For + example, the following command will create a sparse 100 meg file full + of zeroes. + + + host% + dd if=/dev/zero of=new_filesystem seek=100 count=1 bs=1M + + + + + + + 8.2. Assign the file to a UML device + + Add an argument like the following to the UML command line: + + ubd4=new_filesystem + + + + + making sure that you use an unassigned ubd device number. + + + + 8.3. Creating and mounting the filesystem + + Make sure that the filesystem is available, either by being built into + the kernel, or available as a module, then boot up UML and log in. If + the root filesystem doesn't have the filesystem utilities (mkfs, fsck, + etc), then get them into UML by way of the net or hostfs. + + + Make the new filesystem on the device assigned to the new file: + + + host# mkreiserfs /dev/ubd/4 + + + <----------- MKREISERFSv2 -----------> + + ReiserFS version 3.6.25 + Block size 4096 bytes + Block count 25856 + Used blocks 8212 + Journal - 8192 blocks (18-8209), journal header is in block 8210 + Bitmaps: 17 + Root block 8211 + Hash function "r5" + ATTENTION: ALL DATA WILL BE LOST ON '/dev/ubd/4'! (y/n)y + journal size 8192 (from 18) + Initializing journal - 0%....20%....40%....60%....80%....100% + Syncing..done. + + + + + Now, mount it: + + + UML# + mount /dev/ubd/4 /mnt + + + + + and you're in business. + + + + + + + + + + 9. Host file access + + + If you want to access files on the host machine from inside UML, you + can treat it as a separate machine and either nfs mount directories + from the host or copy files into the virtual machine with scp or rcp. + However, since UML is running on the host, it can access those + files just like any other process and make them available inside the + virtual machine without needing to use the network. + + + This is now possible with the hostfs virtual filesystem. With it, you + can mount a host directory into the UML filesystem and access the + files contained in it just as you would on the host. + + + 9.1. Using hostfs + + To begin with, make sure that hostfs is available inside the virtual + machine with + + + UML# cat /proc/filesystems + + + + . hostfs should be listed. If it's not, either rebuild the kernel + with hostfs configured into it or make sure that hostfs is built as a + module and available inside the virtual machine, and insmod it. + + + Now all you need to do is run mount: + + + UML# mount none /mnt/host -t hostfs + + + + + will mount the host's / on the virtual machine's /mnt/host. + + + If you don't want to mount the host root directory, then you can + specify a subdirectory to mount with the -o switch to mount: + + + UML# mount none /mnt/home -t hostfs -o /home + + + + + will mount the hosts's /home on the virtual machine's /mnt/home. + + + + 9.2. hostfs as the root filesystem + + It's possible to boot from a directory hierarchy on the host using + hostfs rather than using the standard filesystem in a file. + + To start, you need that hierarchy. The easiest way is to loop mount + an existing root_fs file: + + + host# mount root_fs uml_root_dir -o loop + + + + + You need to change the filesystem type of / in etc/fstab to be + 'hostfs', so that line looks like this: + + /dev/ubd/0 / hostfs defaults 1 1 + + + + + Then you need to chown to yourself all the files in that directory + that are owned by root. This worked for me: + + + host# find . -uid 0 -exec chown jdike {} \; + + + + + Next, make sure that your UML kernel has hostfs compiled in, not as a + module. Then run UML with the boot device pointing at that directory: + + + ubd0=/path/to/uml/root/directory + + + + + UML should then boot as it does normally. + + + 9.3. Building hostfs + + If you need to build hostfs because it's not in your kernel, you have + two choices: + + + + o Compiling hostfs into the kernel: + + + Reconfigure the kernel and set the 'Host filesystem' option under + + + o Compiling hostfs as a module: + + + Reconfigure the kernel and set the 'Host filesystem' option under + be in arch/um/fs/hostfs/hostfs.o. Install that in + /lib/modules/`uname -r`/fs in the virtual machine, boot it up, and + + + UML# insmod hostfs + + + + + + + + + + + + + 10. The Management Console + + + + The UML management console is a low-level interface to the kernel, + somewhat like the i386 SysRq interface. Since there is a full-blown + operating system under UML, there is much greater flexibility possible + than with the SysRq mechanism. + + + There are a number of things you can do with the mconsole interface: + + o get the kernel version + + o add and remove devices + + o halt or reboot the machine + + o Send SysRq commands + + o Pause and resume the UML + + + You need the mconsole client (uml_mconsole) which is present in CVS + (/tools/mconsole) in 2.4.5-9um and later, and will be in the RPM in + 2.4.6. + + + You also need CONFIG_MCONSOLE (under 'General Setup') enabled in UML. + When you boot UML, you'll see a line like: + + + mconsole initialized on /home/jdike/.uml/umlNJ32yL/mconsole + + + + + If you specify a unique machine id one the UML command line, i.e. + + + umid=debian + + + + + you'll see this + + + mconsole initialized on /home/jdike/.uml/debian/mconsole + + + + + That file is the socket that uml_mconsole will use to communicate with + UML. Run it with either the umid or the full path as its argument: + + + host% uml_mconsole debian + + + + + or + + + host% uml_mconsole /home/jdike/.uml/debian/mconsole + + + + + You'll get a prompt, at which you can run one of these commands: + + o version + + o halt + + o reboot + + o config + + o remove + + o sysrq + + o help + + o cad + + o stop + + o go + + + 10.1. version + + This takes no arguments. It prints the UML version. + + + (mconsole) version + OK Linux usermode 2.4.5-9um #1 Wed Jun 20 22:47:08 EDT 2001 i686 + + + + + There are a couple actual uses for this. It's a simple no-op which + can be used to check that a UML is running. It's also a way of + sending an interrupt to the UML. This is sometimes useful on SMP + hosts, where there's a bug which causes signals to UML to be lost, + often causing it to appear to hang. Sending such a UML the mconsole + version command is a good way to 'wake it up' before networking has + been enabled, as it does not do anything to the function of the UML. + + + + 10.2. halt and reboot + + These take no arguments. They shut the machine down immediately, with + no syncing of disks and no clean shutdown of userspace. So, they are + pretty close to crashing the machine. + + + (mconsole) halt + OK + + + + + + + 10.3. config + + "config" adds a new device to the virtual machine. Currently the ubd + and network drivers support this. It takes one argument, which is the + device to add, with the same syntax as the kernel command line. + + + + + (mconsole) + config ubd3=/home/jdike/incoming/roots/root_fs_debian22 + + OK + (mconsole) config eth1=mcast + OK + + + + + + + 10.4. remove + + "remove" deletes a device from the system. Its argument is just the + name of the device to be removed. The device must be idle in whatever + sense the driver considers necessary. In the case of the ubd driver, + the removed block device must not be mounted, swapped on, or otherwise + open, and in the case of the network driver, the device must be down. + + + (mconsole) remove ubd3 + OK + (mconsole) remove eth1 + OK + + + + + + + 10.5. sysrq + + This takes one argument, which is a single letter. It calls the + generic kernel's SysRq driver, which does whatever is called for by + that argument. See the SysRq documentation in + Documentation/admin-guide/sysrq.rst in your favorite kernel tree to + see what letters are valid and what they do. + + + + 10.6. help + + "help" returns a string listing the valid commands and what each one + does. + + + + 10.7. cad + + This invokes the Ctl-Alt-Del action on init. What exactly this ends + up doing is up to /etc/inittab. Normally, it reboots the machine. + With UML, this is usually not desired, so if a halt would be better, + then find the section of inittab that looks like this + + + # What to do when CTRL-ALT-DEL is pressed. + ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now + + + + + and change the command to halt. + + + + 10.8. stop + + This puts the UML in a loop reading mconsole requests until a 'go' + mconsole command is received. This is very useful for making backups + of UML filesystems, as the UML can be stopped, then synced via 'sysrq + s', so that everything is written to the filesystem. You can then copy + the filesystem and then send the UML 'go' via mconsole. + + + Note that a UML running with more than one CPU will have problems + after you send the 'stop' command, as only one CPU will be held in a + mconsole loop and all others will continue as normal. This is a bug, + and will be fixed. + + + + 10.9. go + + This resumes a UML after being paused by a 'stop' command. Note that + when the UML has resumed, TCP connections may have timed out and if + the UML is paused for a long period of time, crond might go a little + crazy, running all the jobs it didn't do earlier. + + + + + + + + + 11. Kernel debugging + + + Note: The interface that makes debugging, as described here, possible + is present in 2.4.0-test6 kernels and later. + + + Since the user-mode kernel runs as a normal Linux process, it is + possible to debug it with gdb almost like any other process. It is + slightly different because the kernel's threads are already being + ptraced for system call interception, so gdb can't ptrace them. + However, a mechanism has been added to work around that problem. + + + In order to debug the kernel, you need build it from source. See + ``Compiling the kernel and modules'' for information on doing that. + Make sure that you enable CONFIG_DEBUGSYM and CONFIG_PT_PROXY during + the config. These will compile the kernel with -g, and enable the + ptrace proxy so that gdb works with UML, respectively. + + + + + 11.1. Starting the kernel under gdb + + You can have the kernel running under the control of gdb from the + beginning by putting 'debug' on the command line. You will get an + xterm with gdb running inside it. The kernel will send some commands + to gdb which will leave it stopped at the beginning of start_kernel. + At this point, you can get things going with 'next', 'step', or + 'cont'. + + + There is a transcript of a debugging session here <debug- + session.html> , with breakpoints being set in the scheduler and in an + interrupt handler. + 11.2. Examining sleeping processes + + Not every bug is evident in the currently running process. Sometimes, + processes hang in the kernel when they shouldn't because they've + deadlocked on a semaphore or something similar. In this case, when + you ^C gdb and get a backtrace, you will see the idle thread, which + isn't very relevant. + + + What you want is the stack of whatever process is sleeping when it + shouldn't be. You need to figure out which process that is, which is + generally fairly easy. Then you need to get its host process id, + which you can do either by looking at ps on the host or at + task.thread.extern_pid in gdb. + + + Now what you do is this: + + o detach from the current thread + + + (UML gdb) det + + + + + + o attach to the thread you are interested in + + + (UML gdb) att <host pid> + + + + + + o look at its stack and anything else of interest + + + (UML gdb) bt + + + + + Note that you can't do anything at this point that requires that a + process execute, e.g. calling a function + + o when you're done looking at that process, reattach to the current + thread and continue it + + + (UML gdb) + att 1 + + + + + + + (UML gdb) + c + + + + + Here, specifying any pid which is not the process id of a UML thread + will cause gdb to reattach to the current thread. I commonly use 1, + but any other invalid pid would work. + + + + 11.3. Running ddd on UML + + ddd works on UML, but requires a special kludge. The process goes + like this: + + o Start ddd + + + host% ddd linux + + + + + + o With ps, get the pid of the gdb that ddd started. You can ask the + gdb to tell you, but for some reason that confuses things and + causes a hang. + + o run UML with 'debug=parent gdb-pid=<pid>' added to the command line + - it will just sit there after you hit return + + o type 'att 1' to the ddd gdb and you will see something like + + + 0xa013dc51 in __kill () + + + (gdb) + + + + + + o At this point, type 'c', UML will boot up, and you can use ddd just + as you do on any other process. + + + + 11.4. Debugging modules + + gdb has support for debugging code which is dynamically loaded into + the process. This support is what is needed to debug kernel modules + under UML. + + + Using that support is somewhat complicated. You have to tell gdb what + object file you just loaded into UML and where in memory it is. Then, + it can read the symbol table, and figure out where all the symbols are + from the load address that you provided. It gets more interesting + when you load the module again (i.e. after an rmmod). You have to + tell gdb to forget about all its symbols, including the main UML ones + for some reason, then load then all back in again. + + + There's an easy way and a hard way to do this. The easy way is to use + the umlgdb expect script written by Chandan Kudige. It basically + automates the process for you. + + + First, you must tell it where your modules are. There is a list in + the script that looks like this: + set MODULE_PATHS { + "fat" "/usr/src/uml/linux-2.4.18/fs/fat/fat.o" + "isofs" "/usr/src/uml/linux-2.4.18/fs/isofs/isofs.o" + "minix" "/usr/src/uml/linux-2.4.18/fs/minix/minix.o" + } + + + + + You change that to list the names and paths of the modules that you + are going to debug. Then you run it from the toplevel directory of + your UML pool and it basically tells you what to do: + + + + + ******** GDB pid is 21903 ******** + Start UML as: ./linux <kernel switches> debug gdb-pid=21903 + + + + GNU gdb 5.0rh-5 Red Hat Linux 7.1 + Copyright 2001 Free Software Foundation, Inc. + GDB is free software, covered by the GNU General Public License, and you are + welcome to change it and/or distribute copies of it under certain conditions. + Type "show copying" to see the conditions. + There is absolutely no warranty for GDB. Type "show warranty" for details. + This GDB was configured as "i386-redhat-linux"... + (gdb) b sys_init_module + Breakpoint 1 at 0xa0011923: file module.c, line 349. + (gdb) att 1 + + + + + After you run UML and it sits there doing nothing, you hit return at + the 'att 1' and continue it: + + + Attaching to program: /home/jdike/linux/2.4/um/./linux, process 1 + 0xa00f4221 in __kill () + (UML gdb) c + Continuing. + + + + + At this point, you debug normally. When you insmod something, the + expect magic will kick in and you'll see something like: + + + + + + + + + + + + + + + + + + *** Module hostfs loaded *** + Breakpoint 1, sys_init_module (name_user=0x805abb0 "hostfs", + mod_user=0x8070e00) at module.c:349 + 349 char *name, *n_name, *name_tmp = NULL; + (UML gdb) finish + Run till exit from #0 sys_init_module (name_user=0x805abb0 "hostfs", + mod_user=0x8070e00) at module.c:349 + 0xa00e2e23 in execute_syscall (r=0xa8140284) at syscall_kern.c:411 + 411 else res = EXECUTE_SYSCALL(syscall, regs); + Value returned is $1 = 0 + (UML gdb) + p/x (int)module_list + module_list->size_of_struct + + $2 = 0xa9021054 + (UML gdb) symbol-file ./linux + Load new symbol table from "./linux"? (y or n) y + Reading symbols from ./linux... + done. + (UML gdb) + add-symbol-file /home/jdike/linux/2.4/um/arch/um/fs/hostfs/hostfs.o 0xa9021054 + + add symbol table from file "/home/jdike/linux/2.4/um/arch/um/fs/hostfs/hostfs.o" at + .text_addr = 0xa9021054 + (y or n) y + + Reading symbols from /home/jdike/linux/2.4/um/arch/um/fs/hostfs/hostfs.o... + done. + (UML gdb) p *module_list + $1 = {size_of_struct = 84, next = 0xa0178720, name = 0xa9022de0 "hostfs", + size = 9016, uc = {usecount = {counter = 0}, pad = 0}, flags = 1, + nsyms = 57, ndeps = 0, syms = 0xa9023170, deps = 0x0, refs = 0x0, + init = 0xa90221f0 <init_hostfs>, cleanup = 0xa902222c <exit_hostfs>, + ex_table_start = 0x0, ex_table_end = 0x0, persist_start = 0x0, + persist_end = 0x0, can_unload = 0, runsize = 0, kallsyms_start = 0x0, + kallsyms_end = 0x0, + archdata_start = 0x1b855 <Address 0x1b855 out of bounds>, + archdata_end = 0xe5890000 <Address 0xe5890000 out of bounds>, + kernel_data = 0xf689c35d <Address 0xf689c35d out of bounds>} + >> Finished loading symbols for hostfs ... + + + + + That's the easy way. It's highly recommended. The hard way is + described below in case you're interested in what's going on. + + + Boot the kernel under the debugger and load the module with insmod or + modprobe. With gdb, do: + + + (UML gdb) p module_list + + + + + This is a list of modules that have been loaded into the kernel, with + the most recently loaded module first. Normally, the module you want + is at module_list. If it's not, walk down the next links, looking at + the name fields until find the module you want to debug. Take the + address of that structure, and add module.size_of_struct (which in + 2.4.10 kernels is 96 (0x60)) to it. Gdb can make this hard addition + for you :-): + + + + (UML gdb) + printf "%#x\n", (int)module_list module_list->size_of_struct + + + + + The offset from the module start occasionally changes (before 2.4.0, + it was module.size_of_struct + 4), so it's a good idea to check the + init and cleanup addresses once in a while, as describe below. Now + do: + + + (UML gdb) + add-symbol-file /path/to/module/on/host that_address + + + + + Tell gdb you really want to do it, and you're in business. + + + If there's any doubt that you got the offset right, like breakpoints + appear not to work, or they're appearing in the wrong place, you can + check it by looking at the module structure. The init and cleanup + fields should look like: + + + init = 0x588066b0 <init_hostfs>, cleanup = 0x588066c0 <exit_hostfs> + + + + + with no offsets on the symbol names. If the names are right, but they + are offset, then the offset tells you how much you need to add to the + address you gave to add-symbol-file. + + + When you want to load in a new version of the module, you need to get + gdb to forget about the old one. The only way I've found to do that + is to tell gdb to forget about all symbols that it knows about: + + + (UML gdb) symbol-file + + + + + Then reload the symbols from the kernel binary: + + + (UML gdb) symbol-file /path/to/kernel + + + + + and repeat the process above. You'll also need to re-enable break- + points. They were disabled when you dumped all the symbols because + gdb couldn't figure out where they should go. + + + + 11.5. Attaching gdb to the kernel + + If you don't have the kernel running under gdb, you can attach gdb to + it later by sending the tracing thread a SIGUSR1. The first line of + the console output identifies its pid: + tracing thread pid = 20093 + + + + + When you send it the signal: + + + host% kill -USR1 20093 + + + + + you will get an xterm with gdb running in it. + + + If you have the mconsole compiled into UML, then the mconsole client + can be used to start gdb: + + + (mconsole) (mconsole) config gdb=xterm + + + + + will fire up an xterm with gdb running in it. + + + + 11.6. Using alternate debuggers + + UML has support for attaching to an already running debugger rather + than starting gdb itself. This is present in CVS as of 17 Apr 2001. + I sent it to Alan for inclusion in the ac tree, and it will be in my + 2.4.4 release. + + + This is useful when gdb is a subprocess of some UI, such as emacs or + ddd. It can also be used to run debuggers other than gdb on UML. + Below is an example of using strace as an alternate debugger. + + + To do this, you need to get the pid of the debugger and pass it in + with the + + + If you are using gdb under some UI, then tell it to 'att 1', and + you'll find yourself attached to UML. + + + If you are using something other than gdb as your debugger, then + you'll need to get it to do the equivalent of 'att 1' if it doesn't do + it automatically. + + + An example of an alternate debugger is strace. You can strace the + actual kernel as follows: + + o Run the following in a shell + + + host% + sh -c 'echo pid=$$; echo -n hit return; read x; exec strace -p 1 -o strace.out' + + + + o Run UML with 'debug' and 'gdb-pid=<pid>' with the pid printed out + by the previous command + + o Hit return in the shell, and UML will start running, and strace + output will start accumulating in the output file. + + Note that this is different from running + + + host% strace ./linux + + + + + That will strace only the main UML thread, the tracing thread, which + doesn't do any of the actual kernel work. It just oversees the vir- + tual machine. In contrast, using strace as described above will show + you the low-level activity of the virtual machine. + + + + + + 12. Kernel debugging examples + + 12.1. The case of the hung fsck + + When booting up the kernel, fsck failed, and dropped me into a shell + to fix things up. I ran fsck -y, which hung: + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Setting hostname uml [ OK ] + Checking root filesystem + /dev/fhd0 was not cleanly unmounted, check forced. + Error reading block 86894 (Attempt to read block from filesystem resulted in short read) while reading indirect blocks of inode 19780. + + /dev/fhd0: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY. + (i.e., without -a or -p options) + [ FAILED ] + + *** An error occurred during the file system check. + *** Dropping you to a shell; the system will reboot + *** when you leave the shell. + Give root password for maintenance + (or type Control-D for normal startup): + + [root@uml /root]# fsck -y /dev/fhd0 + fsck -y /dev/fhd0 + Parallelizing fsck version 1.14 (9-Jan-1999) + e2fsck 1.14, 9-Jan-1999 for EXT2 FS 0.5b, 95/08/09 + /dev/fhd0 contains a file system with errors, check forced. + Pass 1: Checking inodes, blocks, and sizes + Error reading block 86894 (Attempt to read block from filesystem resulted in short read) while reading indirect blocks of inode 19780. Ignore error? yes + + Inode 19780, i_blocks is 1548, should be 540. Fix? yes + + Pass 2: Checking directory structure + Error reading block 49405 (Attempt to read block from filesystem resulted in short read). Ignore error? yes + + Directory inode 11858, block 0, offset 0: directory corrupted + Salvage? yes + + Missing '.' in directory inode 11858. + Fix? yes + + Missing '..' in directory inode 11858. + Fix? yes + + + + + + The standard drill in this sort of situation is to fire up gdb on the + signal thread, which, in this case, was pid 1935. In another window, + I run gdb and attach pid 1935. + + + + + ~/linux/2.3.26/um 1016: gdb linux + GNU gdb 4.17.0.11 with Linux support + Copyright 1998 Free Software Foundation, Inc. + GDB is free software, covered by the GNU General Public License, and you are + welcome to change it and/or distribute copies of it under certain conditions. + Type "show copying" to see the conditions. + There is absolutely no warranty for GDB. Type "show warranty" for details. + This GDB was configured as "i386-redhat-linux"... + + (gdb) att 1935 + Attaching to program `/home/dike/linux/2.3.26/um/linux', Pid 1935 + 0x100756d9 in __wait4 () + + + + + + + Let's see what's currently running: + + + + (gdb) p current_task.pid + $1 = 0 + + + + + + It's the idle thread, which means that fsck went to sleep for some + reason and never woke up. + + + Let's guess that the last process in the process list is fsck: + + + + (gdb) p current_task.prev_task.comm + $13 = "fsck.ext2\000\000\000\000\000\000" + + + + + + It is, so let's see what it thinks it's up to: + + + + (gdb) p current_task.prev_task.thread + $14 = {extern_pid = 1980, tracing = 0, want_tracing = 0, forking = 0, + kernel_stack_page = 0, signal_stack = 1342627840, syscall = {id = 4, args = { + 3, 134973440, 1024, 0, 1024}, have_result = 0, result = 50590720}, + request = {op = 2, u = {exec = {ip = 1350467584, sp = 2952789424}, fork = { + regs = {1350467584, 2952789424, 0 <repeats 15 times>}, sigstack = 0, + pid = 0}, switch_to = 0x507e8000, thread = {proc = 0x507e8000, + arg = 0xaffffdb0, flags = 0, new_pid = 0}, input_request = { + op = 1350467584, fd = -1342177872, proc = 0, pid = 0}}}} + + + + + + The interesting things here are the fact that its .thread.syscall.id + is __NR_write (see the big switch in arch/um/kernel/syscall_kern.c or + the defines in include/asm-um/arch/unistd.h), and that it never + returned. Also, its .request.op is OP_SWITCH (see + arch/um/include/user_util.h). These mean that it went into a write, + and, for some reason, called schedule(). + + + The fact that it never returned from write means that its stack should + be fairly interesting. Its pid is 1980 (.thread.extern_pid). That + process is being ptraced by the signal thread, so it must be detached + before gdb can attach it: + + + + + + + + + + + (gdb) call detach(1980) + + Program received signal SIGSEGV, Segmentation fault. + <function called from gdb> + The program being debugged stopped while in a function called from GDB. + When the function (detach) is done executing, GDB will silently + stop (instead of continuing to evaluate the expression containing + the function call). + (gdb) call detach(1980) + $15 = 0 + + + + + + The first detach segfaults for some reason, and the second one + succeeds. + + + Now I detach from the signal thread, attach to the fsck thread, and + look at its stack: + + + (gdb) det + Detaching from program: /home/dike/linux/2.3.26/um/linux Pid 1935 + (gdb) att 1980 + Attaching to program `/home/dike/linux/2.3.26/um/linux', Pid 1980 + 0x10070451 in __kill () + (gdb) bt + #0 0x10070451 in __kill () + #1 0x10068ccd in usr1_pid (pid=1980) at process.c:30 + #2 0x1006a03f in _switch_to (prev=0x50072000, next=0x507e8000) + at process_kern.c:156 + #3 0x1006a052 in switch_to (prev=0x50072000, next=0x507e8000, last=0x50072000) + at process_kern.c:161 + #4 0x10001d12 in schedule () at core.c:777 + #5 0x1006a744 in __down (sem=0x507d241c) at semaphore.c:71 + #6 0x1006aa10 in __down_failed () at semaphore.c:157 + #7 0x1006c5d8 in segv_handler (sc=0x5006e940) at trap_user.c:174 + #8 0x1006c5ec in kern_segv_handler (sig=11) at trap_user.c:182 + #9 <signal handler called> + #10 0x10155404 in errno () + #11 0x1006c0aa in segv (address=1342179328, is_write=2) at trap_kern.c:50 + #12 0x1006c5d8 in segv_handler (sc=0x5006eaf8) at trap_user.c:174 + #13 0x1006c5ec in kern_segv_handler (sig=11) at trap_user.c:182 + #14 <signal handler called> + #15 0xc0fd in ?? () + #16 0x10016647 in sys_write (fd=3, + buf=0x80b8800 <Address 0x80b8800 out of bounds>, count=1024) + at read_write.c:159 + #17 0x1006d5b3 in execute_syscall (syscall=4, args=0x5006ef08) + at syscall_kern.c:254 + #18 0x1006af87 in really_do_syscall (sig=12) at syscall_user.c:35 + #19 <signal handler called> + #20 0x400dc8b0 in ?? () + + + + + + The interesting things here are : + + o There are two segfaults on this stack (frames 9 and 14) + + o The first faulting address (frame 11) is 0x50000800 + + (gdb) p (void *)1342179328 + $16 = (void *) 0x50000800 + + + + + + The initial faulting address is interesting because it is on the idle + thread's stack. I had been seeing the idle thread segfault for no + apparent reason, and the cause looked like stack corruption. In hopes + of catching the culprit in the act, I had turned off all protections + to that stack while the idle thread wasn't running. This apparently + tripped that trap. + + + However, the more immediate problem is that second segfault and I'm + going to concentrate on that. First, I want to see where the fault + happened, so I have to go look at the sigcontent struct in frame 8: + + + + (gdb) up + #1 0x10068ccd in usr1_pid (pid=1980) at process.c:30 + 30 kill(pid, SIGUSR1); + (gdb) + #2 0x1006a03f in _switch_to (prev=0x50072000, next=0x507e8000) + at process_kern.c:156 + 156 usr1_pid(getpid()); + (gdb) + #3 0x1006a052 in switch_to (prev=0x50072000, next=0x507e8000, last=0x50072000) + at process_kern.c:161 + 161 _switch_to(prev, next); + (gdb) + #4 0x10001d12 in schedule () at core.c:777 + 777 switch_to(prev, next, prev); + (gdb) + #5 0x1006a744 in __down (sem=0x507d241c) at semaphore.c:71 + 71 schedule(); + (gdb) + #6 0x1006aa10 in __down_failed () at semaphore.c:157 + 157 } + (gdb) + #7 0x1006c5d8 in segv_handler (sc=0x5006e940) at trap_user.c:174 + 174 segv(sc->cr2, sc->err & 2); + (gdb) + #8 0x1006c5ec in kern_segv_handler (sig=11) at trap_user.c:182 + 182 segv_handler(sc); + (gdb) p *sc + Cannot access memory at address 0x0. + + + + + That's not very useful, so I'll try a more manual method: + + + (gdb) p *((struct sigcontext *) (&sig + 1)) + $19 = {gs = 0, __gsh = 0, fs = 0, __fsh = 0, es = 43, __esh = 0, ds = 43, + __dsh = 0, edi = 1342179328, esi = 1350378548, ebp = 1342630440, + esp = 1342630420, ebx = 1348150624, edx = 1280, ecx = 0, eax = 0, + trapno = 14, err = 4, eip = 268480945, cs = 35, __csh = 0, eflags = 66118, + esp_at_signal = 1342630420, ss = 43, __ssh = 0, fpstate = 0x0, oldmask = 0, + cr2 = 1280} + + + + The ip is in handle_mm_fault: + + + (gdb) p (void *)268480945 + $20 = (void *) 0x1000b1b1 + (gdb) i sym $20 + handle_mm_fault + 57 in section .text + + + + + + Specifically, it's in pte_alloc: + + + (gdb) i line *$20 + Line 124 of "/home/dike/linux/2.3.26/um/include/asm/pgalloc.h" + starts at address 0x1000b1b1 <handle_mm_fault+57> + and ends at 0x1000b1b7 <handle_mm_fault+63>. + + + + + + To find where in handle_mm_fault this is, I'll jump forward in the + code until I see an address in that procedure: + + + + (gdb) i line *0x1000b1c0 + Line 126 of "/home/dike/linux/2.3.26/um/include/asm/pgalloc.h" + starts at address 0x1000b1b7 <handle_mm_fault+63> + and ends at 0x1000b1c3 <handle_mm_fault+75>. + (gdb) i line *0x1000b1d0 + Line 131 of "/home/dike/linux/2.3.26/um/include/asm/pgalloc.h" + starts at address 0x1000b1d0 <handle_mm_fault+88> + and ends at 0x1000b1da <handle_mm_fault+98>. + (gdb) i line *0x1000b1e0 + Line 61 of "/home/dike/linux/2.3.26/um/include/asm/pgalloc.h" + starts at address 0x1000b1da <handle_mm_fault+98> + and ends at 0x1000b1e1 <handle_mm_fault+105>. + (gdb) i line *0x1000b1f0 + Line 134 of "/home/dike/linux/2.3.26/um/include/asm/pgalloc.h" + starts at address 0x1000b1f0 <handle_mm_fault+120> + and ends at 0x1000b200 <handle_mm_fault+136>. + (gdb) i line *0x1000b200 + Line 135 of "/home/dike/linux/2.3.26/um/include/asm/pgalloc.h" + starts at address 0x1000b200 <handle_mm_fault+136> + and ends at 0x1000b208 <handle_mm_fault+144>. + (gdb) i line *0x1000b210 + Line 139 of "/home/dike/linux/2.3.26/um/include/asm/pgalloc.h" + starts at address 0x1000b210 <handle_mm_fault+152> + and ends at 0x1000b219 <handle_mm_fault+161>. + (gdb) i line *0x1000b220 + Line 1168 of "memory.c" starts at address 0x1000b21e <handle_mm_fault+166> + and ends at 0x1000b222 <handle_mm_fault+170>. + + + + + + Something is apparently wrong with the page tables or vma_structs, so + lets go back to frame 11 and have a look at them: + + + + #11 0x1006c0aa in segv (address=1342179328, is_write=2) at trap_kern.c:50 + 50 handle_mm_fault(current, vma, address, is_write); + (gdb) call pgd_offset_proc(vma->vm_mm, address) + $22 = (pgd_t *) 0x80a548c + + + + + + That's pretty bogus. Page tables aren't supposed to be in process + text or data areas. Let's see what's in the vma: + + + (gdb) p *vma + $23 = {vm_mm = 0x507d2434, vm_start = 0, vm_end = 134512640, + vm_next = 0x80a4f8c, vm_page_prot = {pgprot = 0}, vm_flags = 31200, + vm_avl_height = 2058, vm_avl_left = 0x80a8c94, vm_avl_right = 0x80d1000, + vm_next_share = 0xaffffdb0, vm_pprev_share = 0xaffffe63, + vm_ops = 0xaffffe7a, vm_pgoff = 2952789626, vm_file = 0xafffffec, + vm_private_data = 0x62} + (gdb) p *vma.vm_mm + $24 = {mmap = 0x507d2434, mmap_avl = 0x0, mmap_cache = 0x8048000, + pgd = 0x80a4f8c, mm_users = {counter = 0}, mm_count = {counter = 134904288}, + map_count = 134909076, mmap_sem = {count = {counter = 135073792}, + sleepers = -1342177872, wait = {lock = <optimized out or zero length>, + task_list = {next = 0xaffffe63, prev = 0xaffffe7a}, + __magic = -1342177670, __creator = -1342177300}, __magic = 98}, + page_table_lock = {}, context = 138, start_code = 0, end_code = 0, + start_data = 0, end_data = 0, start_brk = 0, brk = 0, start_stack = 0, + arg_start = 0, arg_end = 0, env_start = 0, env_end = 0, rss = 1350381536, + total_vm = 0, locked_vm = 0, def_flags = 0, cpu_vm_mask = 0, swap_cnt = 0, + swap_address = 0, segments = 0x0} + + + + + + This also pretty bogus. With all of the 0x80xxxxx and 0xaffffxxx + addresses, this is looking like a stack was plonked down on top of + these structures. Maybe it's a stack overflow from the next page: + + + + (gdb) p vma + $25 = (struct vm_area_struct *) 0x507d2434 + + + + + + That's towards the lower quarter of the page, so that would have to + have been pretty heavy stack overflow: + + + + + + + + + + + + + + + (gdb) x/100x $25 + 0x507d2434: 0x507d2434 0x00000000 0x08048000 0x080a4f8c + 0x507d2444: 0x00000000 0x080a79e0 0x080a8c94 0x080d1000 + 0x507d2454: 0xaffffdb0 0xaffffe63 0xaffffe7a 0xaffffe7a + 0x507d2464: 0xafffffec 0x00000062 0x0000008a 0x00000000 + 0x507d2474: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2484: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2494: 0x00000000 0x00000000 0x507d2fe0 0x00000000 + 0x507d24a4: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d24b4: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d24c4: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d24d4: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d24e4: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d24f4: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2504: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2514: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2524: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2534: 0x00000000 0x00000000 0x507d25dc 0x00000000 + 0x507d2544: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2554: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2564: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2574: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2584: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d2594: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d25a4: 0x00000000 0x00000000 0x00000000 0x00000000 + 0x507d25b4: 0x00000000 0x00000000 0x00000000 0x00000000 + + + + + + It's not stack overflow. The only "stack-like" piece of this data is + the vma_struct itself. + + + At this point, I don't see any avenues to pursue, so I just have to + admit that I have no idea what's going on. What I will do, though, is + stick a trap on the segfault handler which will stop if it sees any + writes to the idle thread's stack. That was the thing that happened + first, and it may be that if I can catch it immediately, what's going + on will be somewhat clearer. + + + 12.2. Episode 2: The case of the hung fsck + + After setting a trap in the SEGV handler for accesses to the signal + thread's stack, I reran the kernel. + + + fsck hung again, this time by hitting the trap: + + + + + + + + + + + + + + + + + Setting hostname uml [ OK ] + Checking root filesystem + /dev/fhd0 contains a file system with errors, check forced. + Error reading block 86894 (Attempt to read block from filesystem resulted in short read) while reading indirect blocks of inode 19780. + + /dev/fhd0: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY. + (i.e., without -a or -p options) + [ FAILED ] + + *** An error occurred during the file system check. + *** Dropping you to a shell; the system will reboot + *** when you leave the shell. + Give root password for maintenance + (or type Control-D for normal startup): + + [root@uml /root]# fsck -y /dev/fhd0 + fsck -y /dev/fhd0 + Parallelizing fsck version 1.14 (9-Jan-1999) + e2fsck 1.14, 9-Jan-1999 for EXT2 FS 0.5b, 95/08/09 + /dev/fhd0 contains a file system with errors, check forced. + Pass 1: Checking inodes, blocks, and sizes + Error reading block 86894 (Attempt to read block from filesystem resulted in short read) while reading indirect blocks of inode 19780. Ignore error? yes + + Pass 2: Checking directory structure + Error reading block 49405 (Attempt to read block from filesystem resulted in short read). Ignore error? yes + + Directory inode 11858, block 0, offset 0: directory corrupted + Salvage? yes + + Missing '.' in directory inode 11858. + Fix? yes + + Missing '..' in directory inode 11858. + Fix? yes + + Untested (4127) [100fe44c]: trap_kern.c line 31 + + + + + + I need to get the signal thread to detach from pid 4127 so that I can + attach to it with gdb. This is done by sending it a SIGUSR1, which is + caught by the signal thread, which detaches the process: + + + kill -USR1 4127 + + + + + + Now I can run gdb on it: + + + + + + + + + + + + + + ~/linux/2.3.26/um 1034: gdb linux + GNU gdb 4.17.0.11 with Linux support + Copyright 1998 Free Software Foundation, Inc. + GDB is free software, covered by the GNU General Public License, and you are + welcome to change it and/or distribute copies of it under certain conditions. + Type "show copying" to see the conditions. + There is absolutely no warranty for GDB. Type "show warranty" for details. + This GDB was configured as "i386-redhat-linux"... + (gdb) att 4127 + Attaching to program `/home/dike/linux/2.3.26/um/linux', Pid 4127 + 0x10075891 in __libc_nanosleep () + + + + + + The backtrace shows that it was in a write and that the fault address + (address in frame 3) is 0x50000800, which is right in the middle of + the signal thread's stack page: + + + (gdb) bt + #0 0x10075891 in __libc_nanosleep () + #1 0x1007584d in __sleep (seconds=1000000) + at ../sysdeps/unix/sysv/linux/sleep.c:78 + #2 0x1006ce9a in stop () at user_util.c:191 + #3 0x1006bf88 in segv (address=1342179328, is_write=2) at trap_kern.c:31 + #4 0x1006c628 in segv_handler (sc=0x5006eaf8) at trap_user.c:174 + #5 0x1006c63c in kern_segv_handler (sig=11) at trap_user.c:182 + #6 <signal handler called> + #7 0xc0fd in ?? () + #8 0x10016647 in sys_write (fd=3, buf=0x80b8800 "R.", count=1024) + at read_write.c:159 + #9 0x1006d603 in execute_syscall (syscall=4, args=0x5006ef08) + at syscall_kern.c:254 + #10 0x1006af87 in really_do_syscall (sig=12) at syscall_user.c:35 + #11 <signal handler called> + #12 0x400dc8b0 in ?? () + #13 <signal handler called> + #14 0x400dc8b0 in ?? () + #15 0x80545fd in ?? () + #16 0x804daae in ?? () + #17 0x8054334 in ?? () + #18 0x804d23e in ?? () + #19 0x8049632 in ?? () + #20 0x80491d2 in ?? () + #21 0x80596b5 in ?? () + (gdb) p (void *)1342179328 + $3 = (void *) 0x50000800 + + + + + + Going up the stack to the segv_handler frame and looking at where in + the code the access happened shows that it happened near line 110 of + block_dev.c: + + + + + + + + + + (gdb) up + #1 0x1007584d in __sleep (seconds=1000000) + at ../sysdeps/unix/sysv/linux/sleep.c:78 + ../sysdeps/unix/sysv/linux/sleep.c:78: No such file or directory. + (gdb) + #2 0x1006ce9a in stop () at user_util.c:191 + 191 while(1) sleep(1000000); + (gdb) + #3 0x1006bf88 in segv (address=1342179328, is_write=2) at trap_kern.c:31 + 31 KERN_UNTESTED(); + (gdb) + #4 0x1006c628 in segv_handler (sc=0x5006eaf8) at trap_user.c:174 + 174 segv(sc->cr2, sc->err & 2); + (gdb) p *sc + $1 = {gs = 0, __gsh = 0, fs = 0, __fsh = 0, es = 43, __esh = 0, ds = 43, + __dsh = 0, edi = 1342179328, esi = 134973440, ebp = 1342631484, + esp = 1342630864, ebx = 256, edx = 0, ecx = 256, eax = 1024, trapno = 14, + err = 6, eip = 268550834, cs = 35, __csh = 0, eflags = 66070, + esp_at_signal = 1342630864, ss = 43, __ssh = 0, fpstate = 0x0, oldmask = 0, + cr2 = 1342179328} + (gdb) p (void *)268550834 + $2 = (void *) 0x1001c2b2 + (gdb) i sym $2 + block_write + 1090 in section .text + (gdb) i line *$2 + Line 209 of "/home/dike/linux/2.3.26/um/include/asm/arch/string.h" + starts at address 0x1001c2a1 <block_write+1073> + and ends at 0x1001c2bf <block_write+1103>. + (gdb) i line *0x1001c2c0 + Line 110 of "block_dev.c" starts at address 0x1001c2bf <block_write+1103> + and ends at 0x1001c2e3 <block_write+1139>. + + + + + + Looking at the source shows that the fault happened during a call to + copy_from_user to copy the data into the kernel: + + + 107 count -= chars; + 108 copy_from_user(p,buf,chars); + 109 p += chars; + 110 buf += chars; + + + + + + p is the pointer which must contain 0x50000800, since buf contains + 0x80b8800 (frame 8 above). It is defined as: + + + p = offset + bh->b_data; + + + + + + I need to figure out what bh is, and it just so happens that bh is + passed as an argument to mark_buffer_uptodate and mark_buffer_dirty a + few lines later, so I do a little disassembly: + + + + + (gdb) disas 0x1001c2bf 0x1001c2e0 + Dump of assembler code from 0x1001c2bf to 0x1001c2d0: + 0x1001c2bf <block_write+1103>: addl %eax,0xc(%ebp) + 0x1001c2c2 <block_write+1106>: movl 0xfffffdd4(%ebp),%edx + 0x1001c2c8 <block_write+1112>: btsl $0x0,0x18(%edx) + 0x1001c2cd <block_write+1117>: btsl $0x1,0x18(%edx) + 0x1001c2d2 <block_write+1122>: sbbl %ecx,%ecx + 0x1001c2d4 <block_write+1124>: testl %ecx,%ecx + 0x1001c2d6 <block_write+1126>: jne 0x1001c2e3 <block_write+1139> + 0x1001c2d8 <block_write+1128>: pushl $0x0 + 0x1001c2da <block_write+1130>: pushl %edx + 0x1001c2db <block_write+1131>: call 0x1001819c <__mark_buffer_dirty> + End of assembler dump. + + + + + + At that point, bh is in %edx (address 0x1001c2da), which is calculated + at 0x1001c2c2 as %ebp + 0xfffffdd4, so I figure exactly what that is, + taking %ebp from the sigcontext_struct above: + + + (gdb) p (void *)1342631484 + $5 = (void *) 0x5006ee3c + (gdb) p 0x5006ee3c+0xfffffdd4 + $6 = 1342630928 + (gdb) p (void *)$6 + $7 = (void *) 0x5006ec10 + (gdb) p *((void **)$7) + $8 = (void *) 0x50100200 + + + + + + Now, I look at the structure to see what's in it, and particularly, + what its b_data field contains: + + + (gdb) p *((struct buffer_head *)0x50100200) + $13 = {b_next = 0x50289380, b_blocknr = 49405, b_size = 1024, b_list = 0, + b_dev = 15872, b_count = {counter = 1}, b_rdev = 15872, b_state = 24, + b_flushtime = 0, b_next_free = 0x501001a0, b_prev_free = 0x50100260, + b_this_page = 0x501001a0, b_reqnext = 0x0, b_pprev = 0x507fcf58, + b_data = 0x50000800 "", b_page = 0x50004000, + b_end_io = 0x10017f60 <end_buffer_io_sync>, b_dev_id = 0x0, + b_rsector = 98810, b_wait = {lock = <optimized out or zero length>, + task_list = {next = 0x50100248, prev = 0x50100248}, __magic = 1343226448, + __creator = 0}, b_kiobuf = 0x0} + + + + + + The b_data field is indeed 0x50000800, so the question becomes how + that happened. The rest of the structure looks fine, so this probably + is not a case of data corruption. It happened on purpose somehow. + + + The b_page field is a pointer to the page_struct representing the + 0x50000000 page. Looking at it shows the kernel's idea of the state + of that page: + + + + (gdb) p *$13.b_page + $17 = {list = {next = 0x50004a5c, prev = 0x100c5174}, mapping = 0x0, + index = 0, next_hash = 0x0, count = {counter = 1}, flags = 132, lru = { + next = 0x50008460, prev = 0x50019350}, wait = { + lock = <optimized out or zero length>, task_list = {next = 0x50004024, + prev = 0x50004024}, __magic = 1342193708, __creator = 0}, + pprev_hash = 0x0, buffers = 0x501002c0, virtual = 1342177280, + zone = 0x100c5160} + + + + + + Some sanity-checking: the virtual field shows the "virtual" address of + this page, which in this kernel is the same as its "physical" address, + and the page_struct itself should be mem_map[0], since it represents + the first page of memory: + + + + (gdb) p (void *)1342177280 + $18 = (void *) 0x50000000 + (gdb) p mem_map + $19 = (mem_map_t *) 0x50004000 + + + + + + These check out fine. + + + Now to check out the page_struct itself. In particular, the flags + field shows whether the page is considered free or not: + + + (gdb) p (void *)132 + $21 = (void *) 0x84 + + + + + + The "reserved" bit is the high bit, which is definitely not set, so + the kernel considers the signal stack page to be free and available to + be used. + + + At this point, I jump to conclusions and start looking at my early + boot code, because that's where that page is supposed to be reserved. + + + In my setup_arch procedure, I have the following code which looks just + fine: + + + + bootmap_size = init_bootmem(start_pfn, end_pfn - start_pfn); + free_bootmem(__pa(low_physmem) + bootmap_size, high_physmem - low_physmem); + + + + + + Two stack pages have already been allocated, and low_physmem points to + the third page, which is the beginning of free memory. + The init_bootmem call declares the entire memory to the boot memory + manager, which marks it all reserved. The free_bootmem call frees up + all of it, except for the first two pages. This looks correct to me. + + + So, I decide to see init_bootmem run and make sure that it is marking + those first two pages as reserved. I never get that far. + + + Stepping into init_bootmem, and looking at bootmem_map before looking + at what it contains shows the following: + + + + (gdb) p bootmem_map + $3 = (void *) 0x50000000 + + + + + + Aha! The light dawns. That first page is doing double duty as a + stack and as the boot memory map. The last thing that the boot memory + manager does is to free the pages used by its memory map, so this page + is getting freed even its marked as reserved. + + + The fix was to initialize the boot memory manager before allocating + those two stack pages, and then allocate them through the boot memory + manager. After doing this, and fixing a couple of subsequent buglets, + the stack corruption problem disappeared. + + + + + + 13. What to do when UML doesn't work + + + + + 13.1. Strange compilation errors when you build from source + + As of test11, it is necessary to have "ARCH=um" in the environment or + on the make command line for all steps in building UML, including + clean, distclean, or mrproper, config, menuconfig, or xconfig, dep, + and linux. If you forget for any of them, the i386 build seems to + contaminate the UML build. If this happens, start from scratch with + + + host% + make mrproper ARCH=um + + + + + and repeat the build process with ARCH=um on all the steps. + + + See ``Compiling the kernel and modules'' for more details. + + + Another cause of strange compilation errors is building UML in + /usr/src/linux. If you do this, the first thing you need to do is + clean up the mess you made. The /usr/src/linux/asm link will now + point to /usr/src/linux/asm-um. Make it point back to + /usr/src/linux/asm-i386. Then, move your UML pool someplace else and + build it there. Also see below, where a more specific set of symptoms + is described. + + + + 13.3. A variety of panics and hangs with /tmp on a reiserfs filesys- + tem + + I saw this on reiserfs 3.5.21 and it seems to be fixed in 3.5.27. + Panics preceded by + + + Detaching pid nnnn + + + + are diagnostic of this problem. This is a reiserfs bug which causes a + thread to occasionally read stale data from a mmapped page shared with + another thread. The fix is to upgrade the filesystem or to have /tmp + be an ext2 filesystem. + + + + 13.4. The compile fails with errors about conflicting types for + 'open', 'dup', and 'waitpid' + + This happens when you build in /usr/src/linux. The UML build makes + the include/asm link point to include/asm-um. /usr/include/asm points + to /usr/src/linux/include/asm, so when that link gets moved, files + which need to include the asm-i386 versions of headers get the + incompatible asm-um versions. The fix is to move the include/asm link + back to include/asm-i386 and to do UML builds someplace else. + + + + 13.5. UML doesn't work when /tmp is an NFS filesystem + + This seems to be a similar situation with the ReiserFS problem above. + Some versions of NFS seems not to handle mmap correctly, which UML + depends on. The workaround is have /tmp be a non-NFS directory. + + + 13.6. UML hangs on boot when compiled with gprof support + + If you build UML with gprof support and, early in the boot, it does + this + + + kernel BUG at page_alloc.c:100! + + + + + you have a buggy gcc. You can work around the problem by removing + UM_FASTCALL from CFLAGS in arch/um/Makefile-i386. This will open up + another bug, but that one is fairly hard to reproduce. + + + + 13.7. syslogd dies with a SIGTERM on startup + + The exact boot error depends on the distribution that you're booting, + but Debian produces this: + + + /etc/rc2.d/S10sysklogd: line 49: 93 Terminated + start-stop-daemon --start --quiet --exec /sbin/syslogd -- $SYSLOGD + + + + + This is a syslogd bug. There's a race between a parent process + installing a signal handler and its child sending the signal. See + this uml-devel post <http://www.geocrawler.com/lists/3/Source- + Forge/709/0/6612801> for the details. + + + + 13.8. TUN/TAP networking doesn't work on a 2.4 host + + There are a couple of problems which were + <http://www.geocrawler.com/lists/3/SourceForge/597/0/> name="pointed + out"> by Tim Robinson <timro at trkr dot net> + + o It doesn't work on hosts running 2.4.7 (or thereabouts) or earlier. + The fix is to upgrade to something more recent and then read the + next item. + + o If you see + + + File descriptor in bad state + + + + when you bring up the device inside UML, you have a header mismatch + between the original kernel and the upgraded one. Make /usr/src/linux + point at the new headers. This will only be a problem if you build + uml_net yourself. + + + + 13.9. You can network to the host but not to other machines on the + net + + If you can connect to the host, and the host can connect to UML, but + you cannot connect to any other machines, then you may need to enable + IP Masquerading on the host. Usually this is only experienced when + using private IP addresses (192.168.x.x or 10.x.x.x) for host/UML + networking, rather than the public address space that your host is + connected to. UML does not enable IP Masquerading, so you will need + to create a static rule to enable it: + + + host% + iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE + + + + + Replace eth0 with the interface that you use to talk to the rest of + the world. + + + Documentation on IP Masquerading, and SNAT, can be found at + www.netfilter.org <http://www.netfilter.org> . + + + If you can reach the local net, but not the outside Internet, then + that is usually a routing problem. The UML needs a default route: + + + UML# + route add default gw gateway IP + + + + + The gateway IP can be any machine on the local net that knows how to + reach the outside world. Usually, this is the host or the local net- + work's gateway. + + + Occasionally, we hear from someone who can reach some machines, but + not others on the same net, or who can reach some ports on other + machines, but not others. These are usually caused by strange + firewalling somewhere between the UML and the other box. You track + this down by running tcpdump on every interface the packets travel + over and see where they disappear. When you find a machine that takes + the packets in, but does not send them onward, that's the culprit. + + + + 13.10. I have no root and I want to scream + + Thanks to Birgit Wahlich for telling me about this strange one. It + turns out that there's a limit of six environment variables on the + kernel command line. When that limit is reached or exceeded, argument + processing stops, which means that the 'root=' argument that UML + usually adds is not seen. So, the filesystem has no idea what the + root device is, so it panics. + + + The fix is to put less stuff on the command line. Glomming all your + setup variables into one is probably the best way to go. + + + + 13.11. UML build conflict between ptrace.h and ucontext.h + + On some older systems, /usr/include/asm/ptrace.h and + /usr/include/sys/ucontext.h define the same names. So, when they're + included together, the defines from one completely mess up the parsing + of the other, producing errors like: + /usr/include/sys/ucontext.h:47: parse error before + `10' + + + + + plus a pile of warnings. + + + This is a libc botch, which has since been fixed, and I don't see any + way around it besides upgrading. + + + + 13.12. The UML BogoMips is exactly half the host's BogoMips + + On i386 kernels, there are two ways of running the loop that is used + to calculate the BogoMips rating, using the TSC if it's there or using + a one-instruction loop. The TSC produces twice the BogoMips as the + loop. UML uses the loop, since it has nothing resembling a TSC, and + will get almost exactly the same BogoMips as a host using the loop. + However, on a host with a TSC, its BogoMips will be double the loop + BogoMips, and therefore double the UML BogoMips. + + + + 13.13. When you run UML, it immediately segfaults + + If the host is configured with the 2G/2G address space split, that's + why. See ``UML on 2G/2G hosts'' for the details on getting UML to + run on your host. + + + + 13.14. xterms appear, then immediately disappear + + If you're running an up to date kernel with an old release of + uml_utilities, the port-helper program will not work properly, so + xterms will exit straight after they appear. The solution is to + upgrade to the latest release of uml_utilities. Usually this problem + occurs when you have installed a packaged release of UML then compiled + your own development kernel without upgrading the uml_utilities from + the source distribution. + + + + 13.15. Any other panic, hang, or strange behavior + + If you're seeing truly strange behavior, such as hangs or panics that + happen in random places, or you try running the debugger to see what's + happening and it acts strangely, then it could be a problem in the + host kernel. If you're not running a stock Linus or -ac kernel, then + try that. An early version of the preemption patch and a 2.4.10 SuSE + kernel have caused very strange problems in UML. + + + Otherwise, let me know about it. Send a message to one of the UML + mailing lists - either the developer list - user-mode-linux-devel at + lists dot sourceforge dot net (subscription info) or the user list - + user-mode-linux-user at lists dot sourceforge do net (subscription + info), whichever you prefer. Don't assume that everyone knows about + it and that a fix is imminent. + + + If you want to be super-helpful, read ``Diagnosing Problems'' and + follow the instructions contained therein. + 14. Diagnosing Problems + + + If you get UML to crash, hang, or otherwise misbehave, you should + report this on one of the project mailing lists, either the developer + list - user-mode-linux-devel at lists dot sourceforge dot net + (subscription info) or the user list - user-mode-linux-user at lists + dot sourceforge dot net (subscription info). When you do, it is + likely that I will want more information. So, it would be helpful to + read the stuff below, do whatever is applicable in your case, and + report the results to the list. + + + For any diagnosis, you're going to need to build a debugging kernel. + The binaries from this site aren't debuggable. If you haven't done + this before, read about ``Compiling the kernel and modules'' and + ``Kernel debugging'' UML first. + + + 14.1. Case 1 : Normal kernel panics + + The most common case is for a normal thread to panic. To debug this, + you will need to run it under the debugger (add 'debug' to the command + line). An xterm will start up with gdb running inside it. Continue + it when it stops in start_kernel and make it crash. Now ^C gdb and + + + If the panic was a "Kernel mode fault", then there will be a segv + frame on the stack and I'm going to want some more information. The + stack might look something like this: + + + (UML gdb) backtrace + #0 0x1009bf76 in __sigprocmask (how=1, set=0x5f347940, oset=0x0) + at ../sysdeps/unix/sysv/linux/sigprocmask.c:49 + #1 0x10091411 in change_sig (signal=10, on=1) at process.c:218 + #2 0x10094785 in timer_handler (sig=26) at time_kern.c:32 + #3 0x1009bf38 in __restore () + at ../sysdeps/unix/sysv/linux/i386/sigaction.c:125 + #4 0x1009534c in segv (address=8, ip=268849158, is_write=2, is_user=0) + at trap_kern.c:66 + #5 0x10095c04 in segv_handler (sig=11) at trap_user.c:285 + #6 0x1009bf38 in __restore () + + + + + I'm going to want to see the symbol and line information for the value + of ip in the segv frame. In this case, you would do the following: + + + (UML gdb) i sym 268849158 + + + + + and + + + (UML gdb) i line *268849158 + + + + + The reason for this is the __restore frame right above the segv_han- + dler frame is hiding the frame that actually segfaulted. So, I have + to get that information from the faulting ip. + + + 14.2. Case 2 : Tracing thread panics + + The less common and more painful case is when the tracing thread + panics. In this case, the kernel debugger will be useless because it + needs a healthy tracing thread in order to work. The first thing to + do is get a backtrace from the tracing thread. This is done by + figuring out what its pid is, firing up gdb, and attaching it to that + pid. You can figure out the tracing thread pid by looking at the + first line of the console output, which will look like this: + + + tracing thread pid = 15851 + + + + + or by running ps on the host and finding the line that looks like + this: + + + jdike 15851 4.5 0.4 132568 1104 pts/0 S 21:34 0:05 ./linux [(tracing thread)] + + + + + If the panic was 'segfault in signals', then follow the instructions + above for collecting information about the location of the seg fault. + + + If the tracing thread flaked out all by itself, then send that + backtrace in and wait for our crack debugging team to fix the problem. + + + 14.3. Case 3 : Tracing thread panics caused by other threads + + However, there are cases where the misbehavior of another thread + caused the problem. The most common panic of this type is: + + + wait_for_stop failed to wait for <pid> to stop with <signal number> + + + + + In this case, you'll need to get a backtrace from the process men- + tioned in the panic, which is complicated by the fact that the kernel + debugger is defunct and without some fancy footwork, another gdb can't + attach to it. So, this is how the fancy footwork goes: + + In a shell: + + + host% kill -STOP pid + + + + + Run gdb on the tracing thread as described in case 2 and do: + + + (host gdb) call detach(pid) + + + If you get a segfault, do it again. It always works the second time. + + Detach from the tracing thread and attach to that other thread: + + + (host gdb) detach + + + + + + + (host gdb) attach pid + + + + + If gdb hangs when attaching to that process, go back to a shell and + do: + + + host% + kill -CONT pid + + + + + And then get the backtrace: + + + (host gdb) backtrace + + + + + + 14.4. Case 4 : Hangs + + Hangs seem to be fairly rare, but they sometimes happen. When a hang + happens, we need a backtrace from the offending process. Run the + kernel debugger as described in case 1 and get a backtrace. If the + current process is not the idle thread, then send in the backtrace. + You can tell that it's the idle thread if the stack looks like this: + + + #0 0x100b1401 in __libc_nanosleep () + #1 0x100a2885 in idle_sleep (secs=10) at time.c:122 + #2 0x100a546f in do_idle () at process_kern.c:445 + #3 0x100a5508 in cpu_idle () at process_kern.c:471 + #4 0x100ec18f in start_kernel () at init/main.c:592 + #5 0x100a3e10 in start_kernel_proc (unused=0x0) at um_arch.c:71 + #6 0x100a383f in signal_tramp (arg=0x100a3dd8) at trap_user.c:50 + + + + + If this is the case, then some other process is at fault, and went to + sleep when it shouldn't have. Run ps on the host and figure out which + process should not have gone to sleep and stayed asleep. Then attach + to it with gdb and get a backtrace as described in case 3. + + + + + + + 15. Thanks + + + A number of people have helped this project in various ways, and this + page gives recognition where recognition is due. + + + If you're listed here and you would prefer a real link on your name, + or no link at all, instead of the despammed email address pseudo-link, + let me know. + + + If you're not listed here and you think maybe you should be, please + let me know that as well. I try to get everyone, but sometimes my + bookkeeping lapses and I forget about contributions. + + + 15.1. Code and Documentation + + Rusty Russell <rusty at linuxcare.com.au> - + + o wrote the HOWTO <http://user-mode- + linux.sourceforge.net/UserModeLinux-HOWTO.html> + + o prodded me into making this project official and putting it on + SourceForge + + o came up with the way cool UML logo <http://user-mode- + linux.sourceforge.net/uml-small.png> + + o redid the config process + + + Peter Moulder <reiter at netspace.net.au> - Fixed my config and build + processes, and added some useful code to the block driver + + + Bill Stearns <wstearns at pobox.com> - + + o HOWTO updates + + o lots of bug reports + + o lots of testing + + o dedicated a box (uml.ists.dartmouth.edu) to support UML development + + o wrote the mkrootfs script, which allows bootable filesystems of + RPM-based distributions to be cranked out + + o cranked out a large number of filesystems with said script + + + Jim Leu <jleu at mindspring.com> - Wrote the virtual ethernet driver + and associated usermode tools + + Lars Brinkhoff <http://lars.nocrew.org/> - Contributed the ptrace + proxy from his own project <http://a386.nocrew.org/> to allow easier + kernel debugging + + + Andrea Arcangeli <andrea at suse.de> - Redid some of the early boot + code so that it would work on machines with Large File Support + + + Chris Emerson <http://www.chiark.greenend.org.uk/~cemerson/> - Did + the first UML port to Linux/ppc + + + Harald Welte <laforge at gnumonks.org> - Wrote the multicast + transport for the network driver + + + Jorgen Cederlof - Added special file support to hostfs + + + Greg Lonnon <glonnon at ridgerun dot com> - Changed the ubd driver + to allow it to layer a COW file on a shared read-only filesystem and + wrote the iomem emulation support + + + Henrik Nordstrom <http://hem.passagen.se/hno/> - Provided a variety + of patches, fixes, and clues + + + Lennert Buytenhek - Contributed various patches, a rewrite of the + network driver, the first implementation of the mconsole driver, and + did the bulk of the work needed to get SMP working again. + + + Yon Uriarte - Fixed the TUN/TAP network backend while I slept. + + + Adam Heath - Made a bunch of nice cleanups to the initialization code, + plus various other small patches. + + + Matt Zimmerman - Matt volunteered to be the UML Debian maintainer and + is doing a real nice job of it. He also noticed and fixed a number of + actually and potentially exploitable security holes in uml_net. Plus + the occasional patch. I like patches. + + + James McMechan - James seems to have taken over maintenance of the ubd + driver and is doing a nice job of it. + + + Chandan Kudige - wrote the umlgdb script which automates the reloading + of module symbols. + + + Steve Schmidtke - wrote the UML slirp transport and hostaudio drivers, + enabling UML processes to access audio devices on the host. He also + submitted patches for the slip transport and lots of other things. + + + David Coulson <http://davidcoulson.net> - + + o Set up the usermodelinux.org <http://usermodelinux.org> site, + which is a great way of keeping the UML user community on top of + UML goings-on. + + o Site documentation and updates + + o Nifty little UML management daemon UMLd + <http://uml.openconsultancy.com/umld/> + + o Lots of testing and bug reports + + + + + 15.2. Flushing out bugs + + + + o Yuri Pudgorodsky + + o Gerald Britton + + o Ian Wehrman + + o Gord Lamb + + o Eugene Koontz + + o John H. Hartman + + o Anders Karlsson + + o Daniel Phillips + + o John Fremlin + + o Rainer Burgstaller + + o James Stevenson + + o Matt Clay + + o Cliff Jefferies + + o Geoff Hoff + + o Lennert Buytenhek + + o Al Viro + + o Frank Klingenhoefer + + o Livio Baldini Soares + + o Jon Burgess + + o Petru Paler + + o Paul + + o Chris Reahard + + o Sverker Nilsson + + o Gong Su + + o johan verrept + + o Bjorn Eriksson + + o Lorenzo Allegrucci + + o Muli Ben-Yehuda + + o David Mansfield + + o Howard Goff + + o Mike Anderson + + o John Byrne + + o Sapan J. Batia + + o Iris Huang + + o Jan Hudec + + o Voluspa + + + + + 15.3. Buglets and clean-ups + + + + o Dave Zarzycki + + o Adam Lazur + + o Boria Feigin + + o Brian J. Murrell + + o JS + + o Roman Zippel + + o Wil Cooley + + o Ayelet Shemesh + + o Will Dyson + + o Sverker Nilsson + + o dvorak + + o v.naga srinivas + + o Shlomi Fish + + o Roger Binns + + o johan verrept + + o MrChuoi + + o Peter Cleve + + o Vincent Guffens + + o Nathan Scott + + o Patrick Caulfield + + o jbearce + + o Catalin Marinas + + o Shane Spencer + + o Zou Min + + + o Ryan Boder + + o Lorenzo Colitti + + o Gwendal Grignou + + o Andre' Breiler + + o Tsutomu Yasuda + + + + 15.4. Case Studies + + + o Jon Wright + + o William McEwan + + o Michael Richardson + + + + 15.5. Other contributions + + + Bill Carr <Bill.Carr at compaq.com> made the Red Hat mkrootfs script + work with RH 6.2. + + Michael Jennings <mikejen at hevanet.com> sent in some material which + is now gracing the top of the index page <http://user-mode- + linux.sourceforge.net/> of this site. + + SGI <http://www.sgi.com> (and more specifically Ralf Baechle <ralf at + uni-koblenz.de> ) gave me an account on oss.sgi.com + <http://www.oss.sgi.com> . The bandwidth there made it possible to + produce most of the filesystems available on the project download + page. + + Laurent Bonnaud <Laurent.Bonnaud at inpg.fr> took the old grotty + Debian filesystem that I've been distributing and updated it to 2.2. + It is now available by itself here. + + Rik van Riel gave me some ftp space on ftp.nl.linux.org so I can make + releases even when Sourceforge is broken. + + Rodrigo de Castro looked at my broken pte code and told me what was + wrong with it, letting me fix a long-standing (several weeks) and + serious set of bugs. + + Chris Reahard built a specialized root filesystem for running a DNS + server jailed inside UML. It's available from the download + <http://user-mode-linux.sourceforge.net/dl-sf.html> page in the Jail + Filesystems section. + + + + + + + + + + + + |