kernel/linux.git/include/linux/kvm_host.h, branch v6.12.80

KVM: guest_memfd: Remove RCU-protected attribute from slot->gmem.file

2025-11-24T09:36:05+00:00

[ Upstream commit 67b43038ce14d6b0673bdffb2052d879065c94ae ] Remove the RCU-protected attribute from slot->gmem.file. No need to use RCU primitives rcu_assign_pointer()/synchronize_rcu() to update this pointer. - slot->gmem.file is updated in 3 places: kvm_gmem_bind(), kvm_gmem_unbind(), kvm_gmem_release(). All of them are protected by kvm->slots_lock. - slot->gmem.file is read in 2 paths: (1) kvm_gmem_populate kvm_gmem_get_file __kvm_gmem_get_pfn (2) kvm_gmem_get_pfn kvm_gmem_get_file __kvm_gmem_get_pfn Path (1) kvm_gmem_populate() requires holding kvm->slots_lock, so slot->gmem.file is protected by the kvm->slots_lock in this path. Path (2) kvm_gmem_get_pfn() does not require holding kvm->slots_lock. However, it's also not guarded by rcu_read_lock() and rcu_read_unlock(). So synchronize_rcu() in kvm_gmem_unbind()/kvm_gmem_release() actually will not wait for the readers in kvm_gmem_get_pfn() due to lack of RCU read-side critical section. The path (2) kvm_gmem_get_pfn() is safe without RCU protection because: a) kvm_gmem_bind() is called on a new memslot, before the memslot is visible to kvm_gmem_get_pfn(). b) kvm->srcu ensures that kvm_gmem_unbind() and freeing of a memslot occur after the memslot is no longer visible to kvm_gmem_get_pfn(). c) get_file_active() ensures that kvm_gmem_get_pfn() will not access the stale file if kvm_gmem_release() sets it to NULL. This is because if kvm_gmem_release() occurs before kvm_gmem_get_pfn(), get_file_active() will return NULL; if get_file_active() does not return NULL, kvm_gmem_release() should not occur until after kvm_gmem_get_pfn() releases the file reference. Signed-off-by: Yan Zhao Message-ID: <20241104084303.29909-1-yan.y.zhao@intel.com> Signed-off-by: Paolo Bonzini Stable-dep-of: ae431059e75d ("KVM: guest_memfd: Remove bindings on memslot deletion when gmem is dying") Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman

KVM: Add member to struct kvm_gfn_range to indicate private/shared

2025-05-22T12:29:36+00:00

[ Upstream commit dca6c88532322830d5d92486467fcc91b67a9ad8 ] Add new members to strut kvm_gfn_range to indicate which mapping (private-vs-shared) to operate on: enum kvm_gfn_range_filter attr_filter. Update the core zapping operations to set them appropriately. TDX utilizes two GPA aliases for the same memslots, one for memory that is for private memory and one that is for shared. For private memory, KVM cannot always perform the same operations it does on memory for default VMs, such as zapping pages and having them be faulted back in, as this requires guest coordination. However, some operations such as guest driven conversion of memory between private and shared should zap private memory. Internally to the MMU, private and shared mappings are tracked on separate roots. Mapping and zapping operations will operate on the respective GFN alias for each root (private or shared). So zapping operations will by default zap both aliases. Add fields in struct kvm_gfn_range to allow callers to specify which aliases so they can only target the aliases appropriate for their specific operation. There was feedback that target aliases should be specified such that the default value (0) is to operate on both aliases. Several options were considered. Several variations of having separate bools defined such that the default behavior was to process both aliases. They either allowed nonsensical configurations, or were confusing for the caller. A simple enum was also explored and was close, but was hard to process in the caller. Instead, use an enum with the default value (0) reserved as a disallowed value. Catch ranges that didn't have the target aliases specified by looking for that specific value. Set target alias with enum appropriately for these MMU operations: - For KVM's mmu notifier callbacks, zap shared pages only because private pages won't have a userspace mapping - For setting memory attributes, kvm_arch_pre_set_memory_attributes() chooses the aliases based on the attribute. - For guest_memfd invalidations, zap private only. Link: https://lore.kernel.org/kvm/ZivIF9vjKcuGie3s@google.com/ Signed-off-by: Isaku Yamahata Co-developed-by: Rick Edgecombe Signed-off-by: Rick Edgecombe Message-ID: <20240718211230.1492011-3-rick.p.edgecombe@intel.com> Signed-off-by: Paolo Bonzini Stable-dep-of: 9129633d568e ("KVM: x86/mmu: Prevent installing hugepages when mem attributes are changing") Signed-off-by: Sasha Levin

KVM: Allow building irqbypass.ko as as module when kvm.ko is a module

2025-04-20T08:15:54+00:00

commit 459a35111b0a890172a78d51c01b204e13a34a18 upstream. Convert HAVE_KVM_IRQ_BYPASS into a tristate so that selecting IRQ_BYPASS_MANAGER follows KVM={m,y}, i.e. doesn't force irqbypass.ko to be built-in. Note, PPC allows building KVM as a module, but selects HAVE_KVM_IRQ_BYPASS from a boolean Kconfig, i.e. KVM PPC unnecessarily forces irqbpass.ko to be built-in. But that flaw is a longstanding PPC specific issue. Fixes: 61df71ee992d ("kvm: move "select IRQ_BYPASS_MANAGER" to common code") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Message-ID: <20250315024623.2363994-1-seanjc@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman

KVM: Explicitly verify target vCPU is online in kvm_get_vcpu()

2025-02-17T09:05:06+00:00

commit 1e7381f3617d14b3c11da80ff5f8a93ab14cfc46 upstream. Explicitly verify the target vCPU is fully online _prior_ to clamping the index in kvm_get_vcpu(). If the index is "bad", the nospec clamping will generate '0', i.e. KVM will return vCPU0 instead of NULL. In practice, the bug is unlikely to cause problems, as it will only come into play if userspace or the guest is buggy or misbehaving, e.g. KVM may send interrupts to vCPU0 instead of dropping them on the floor. However, returning vCPU0 when it shouldn't exist per online_vcpus is problematic now that KVM uses an xarray for the vCPUs array, as KVM needs to insert into the xarray before publishing the vCPU to userspace (see commit c5b077549136 ("KVM: Convert the kvm->vcpus array to a xarray")), i.e. before vCPU creation is guaranteed to succeed. As a result, incorrectly providing access to vCPU0 will trigger a use-after-free if vCPU0 is dereferenced and kvm_vm_ioctl_create_vcpu() bails out of vCPU creation due to an error and frees vCPU0. Commit afb2acb2e3a3 ("KVM: Fix vcpu_array[0] races") papered over that issue, but in doing so introduced an unsolvable teardown conundrum. Preventing accesses to vCPU0 before it's fully online will allow reverting commit afb2acb2e3a3, without re-introducing the vcpu_array[0] UAF race. Fixes: 1d487e9bf8ba ("KVM: fix spectrev1 gadgets") Cc: stable@vger.kernel.org Cc: Will Deacon Cc: Michal Luczaj Reviewed-by: Pankaj Gupta Acked-by: Will Deacon Link: https://lore.kernel.org/r/20241009150455.1057573-2-seanjc@google.com Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman

KVM: x86: switch hugepage recovery thread to vhost_task

2024-12-05T13:02:43+00:00

commit d96c77bd4eeba469bddbbb14323d2191684da82a upstream. kvm_vm_create_worker_thread() is meant to be used for kthreads that can consume significant amounts of CPU time on behalf of a VM or in response to how the VM behaves (for example how it accesses its memory). Therefore it wants to charge the CPU time consumed by that work to the VM's container. However, because of these threads, cgroups which have kvm instances inside never complete freezing. This can be trivially reproduced: root@test ~# mkdir /sys/fs/cgroup/test root@test ~# echo $$ > /sys/fs/cgroup/test/cgroup.procs root@test ~# qemu-system-x86_64 -nographic -enable-kvm and in another terminal: root@test ~# echo 1 > /sys/fs/cgroup/test/cgroup.freeze root@test ~# cat /sys/fs/cgroup/test/cgroup.events populated 1 frozen 0 The cgroup freezing happens in the signal delivery path but kvm_nx_huge_page_recovery_worker, while joining non-root cgroups, never calls into the signal delivery path and thus never gets frozen. Because the cgroup freezer determines whether a given cgroup is frozen by comparing the number of frozen threads to the total number of threads in the cgroup, the cgroup never becomes frozen and users waiting for the state transition may hang indefinitely. Since the worker kthread is tied to a user process, it's better if it behaves similarly to user tasks as much as possible, including being able to send SIGSTOP and SIGCONT. In fact, vhost_task is all that kvm_vm_create_worker_thread() wanted to be and more: not only it inherits the userspace process's cgroups, it has other niceties like being parented properly in the process tree. Use it instead of the homegrown alternative. Incidentally, the new code is also better behaved when you flip recovery back and forth to disabled and back to enabled. If your recovery period is 1 minute, it will run the next recovery after 1 minute independent of how many times you flipped the parameter. (Commit message based on emails from Tejun). Reported-by: Tejun Heo Reported-by: Luca Boccassi Acked-by: Tejun Heo Tested-by: Luca Boccassi Cc: stable@vger.kernel.org Reviewed-by: Sean Christopherson Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman

KVM: Remove unused kvm_vcpu_gfn_to_pfn_atomic

2024-10-20T11:05:51+00:00

The last use of kvm_vcpu_gfn_to_pfn_atomic was removed by commit 1bbc60d0c7e5 ("KVM: x86/mmu: Remove MMU auditing") Remove it. Signed-off-by: Dr. David Alan Gilbert Message-ID: <20241001141354.18009-3-linux@treblig.org> [Adjust Documentation/virt/kvm/locking.rst. - Paolo] Signed-off-by: Paolo Bonzini

KVM: Remove unused kvm_vcpu_gfn_to_pfn

2024-10-20T11:04:52+00:00

The last use of kvm_vcpu_gfn_to_pfn was removed by commit b1624f99aa8f ("KVM: Remove kvm_vcpu_gfn_to_page() and kvm_vcpu_gpa_to_page()") Remove it. Signed-off-by: Dr. David Alan Gilbert Message-ID: <20241001141354.18009-2-linux@treblig.org> Signed-off-by: Paolo Bonzini

Merge branch 'kvm-redo-enable-virt' into HEAD

2024-09-17T15:38:20+00:00

Register KVM's cpuhp and syscore callbacks when enabling virtualization in hardware, as the sole purpose of said callbacks is to disable and re-enable virtualization as needed. The primary motivation for this series is to simplify dealing with enabling virtualization for Intel's TDX, which needs to enable virtualization when kvm-intel.ko is loaded, i.e. long before the first VM is created. That said, this is a nice cleanup on its own. By registering the callbacks on-demand, the callbacks themselves don't need to check kvm_usage_count, because their very existence implies a non-zero count. Patch 1 (re)adds a dedicated lock for kvm_usage_count. This avoids a lock ordering issue between cpus_read_lock() and kvm_lock. The lock ordering issue still exist in very rare cases, and will be fixed for good by switching vm_list to an (S)RCU-protected list. Signed-off-by: Paolo Bonzini

KVM: Add arch hooks for enabling/disabling virtualization

2024-09-04T15:02:33+00:00

Add arch hooks that are invoked when KVM enables/disable virtualization. x86 will use the hooks to register an "emergency disable" callback, which is essentially an x86-specific shutdown notifier that is used when the kernel is doing an emergency reboot/shutdown/kexec. Add comments for the declarations to help arch code understand exactly when the callbacks are invoked. Alternatively, the APIs themselves could communicate most of the same info, but kvm_arch_pre_enable_virtualization() and kvm_arch_post_disable_virtualization() are a bit cumbersome, and make it a bit less obvious that they are intended to be implemented as a pair. Reviewed-by: Chao Gao Reviewed-by: Kai Huang Acked-by: Kai Huang Tested-by: Farrah Chen Signed-off-by: Sean Christopherson Message-ID: <20240830043600.127750-9-seanjc@google.com> Signed-off-by: Paolo Bonzini

KVM: Rename arch hooks related to per-CPU virtualization enabling

2024-09-04T15:02:33+00:00

Rename the per-CPU hooks used to enable virtualization in hardware to align with the KVM-wide helpers in kvm_main.c, and to better capture that the callbacks are invoked on every online CPU. No functional change intended. Suggested-by: Paolo Bonzini Signed-off-by: Sean Christopherson Reviewed-by: Kai Huang Message-ID: <20240830043600.127750-5-seanjc@google.com> Signed-off-by: Paolo Bonzini