kernel/linux.git/virt/kvm/kvm_main.c, branch linux-7.1.y

KVM: Don't WARN if memory is dirtied without a vCPU when the VM is dying

2026-06-03T14:43:55+00:00

When marking a page dirty, complain about not having a running/loaded vCPU if and only if the VM is still alive, i.e. its refcount is non-zero. This will allow fixing a memory leak for x86 SEV-ES guests without hitting what is effectively a false positive on the WARN. For some SEV-ES VM-Exits, KVM keeps a writable mapping of a guest page across an exit to userspace, and typically unmaps the page on the next KVM_RUN. But if userspace never calls KVM_RUN after such an exit, then KVM needs to unmap the page when the vCPU is destroyed, which in turn triggers the WARN about not having a running vCPU. Alternatively, SEV-ES could temporarily load the vCPU to suppress the WARN, as is done in nested_vmx_free_vcpu() (but for completely unrelated reasons; suppressing WARN from nested_put_vmcs12_pages() is pure happenstance). But loading a vCPU during destruction is gross (ideally nVMX code would be cleaned up), risks complicating the SEV-ES code (KVM would need to ensure the temporarily load()+put() only runs when the vCPU isn't already loaded), and is ultimately pointless. The motivation for the WARN is to guard against KVM dirtying guest memory without pushing the corresponding GFN to the active vCPU's dirty ring, e.g. to ensure userspace doesn't miss a dirty page. But for the VM's refcount to reach zero, there can't be _any_ userspace mappings to the dirty ring, as mapping the dirty ring requires doing mmap() on the vCPU FD. I.e. if userspace had a valid mapping for the dirty ring, then the vCPU file and thus the owning VM would still be alive. And so since userspace can't possibly reach the dirty ring, whether or not KVM technically "misses" a push to the dirty ring is irrelevant. Reported-by: Michael Roth Cc: stable@vger.kernel.org Reviewed-by: Michael Roth Signed-off-by: Sean Christopherson Message-ID: <20260501202250.2115252-15-seanjc@google.com> Signed-off-by: Paolo Bonzini Message-ID: <20260529183549.1104619-15-pbonzini@redhat.com> Signed-off-by: Paolo Bonzini

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2026-04-17T14:18:03+00:00

Pull kvm updates from Paolo Bonzini: "Arm: - Add support for tracing in the standalone EL2 hypervisor code, which should help both debugging and performance analysis. This uses the new infrastructure for 'remote' trace buffers that can be exposed by non-kernel entities such as firmware, and which came through the tracing tree - Add support for GICv5 Per Processor Interrupts (PPIs), as the starting point for supporting the new GIC architecture in KVM - Finally add support for pKVM protected guests, where pages are unmapped from the host as they are faulted into the guest and can be shared back from the guest using pKVM hypercalls. Protected guests are created using a new machine type identifier. As the elusive guestmem has not yet delivered on its promises, anonymous memory is also supported This is only a first step towards full isolation from the host; for example, the CPU register state and DMA accesses are not yet isolated. Because this does not really yet bring fully what it promises, it is hidden behind CONFIG_ARM_PKVM_GUEST + 'kvm-arm.mode=protected', and also triggers TAINT_USER when a VM is created. Caveat emptor - Rework the dreaded user_mem_abort() function to make it more maintainable, reducing the amount of state being exposed to the various helpers and rendering a substantial amount of state immutable - Expand the Stage-2 page table dumper to support NV shadow page tables on a per-VM basis - Tidy up the pKVM PSCI proxy code to be slightly less hard to follow - Fix both SPE and TRBE in non-VHE configurations so that they do not generate spurious, out of context table walks that ultimately lead to very bad HW lockups - A small set of patches fixing the Stage-2 MMU freeing in error cases - Tighten-up accepted SMC immediate value to be only #0 for host SMCCC calls - The usual cleanups and other selftest churn LoongArch: - Use CSR_CRMD_PLV for kvm_arch_vcpu_in_kernel() - Add DMSINTC irqchip in kernel support RISC-V: - Fix steal time shared memory alignment checks - Fix vector context allocation leak - Fix array out-of-bounds in pmu_ctr_read() and pmu_fw_ctr_read_hi() - Fix double-free of sdata in kvm_pmu_clear_snapshot_area() - Fix integer overflow in kvm_pmu_validate_counter_mask() - Fix shift-out-of-bounds in make_xfence_request() - Fix lost write protection on huge pages during dirty logging - Split huge pages during fault handling for dirty logging - Skip CSR restore if VCPU is reloaded on the same core - Implement kvm_arch_has_default_irqchip() for KVM selftests - Factored-out ISA checks into separate sources - Added hideleg to struct kvm_vcpu_config - Factored-out VCPU config into separate sources - Support configuration of per-VM HGATP mode from KVM user space s390: - Support for ESA (31-bit) guests inside nested hypervisors - Remove restriction on memslot alignment, which is not needed anymore with the new gmap code - Fix LPSW/E to update the bear (which of course is the breaking event address register) x86: - Shut up various UBSAN warnings on reading module parameter before they were initialized - Don't zero-allocate page tables that are used for splitting hugepages in the TDP MMU, as KVM is guaranteed to set all SPTEs in the page table and thus write all bytes - As an optimization, bail early when trying to unsync 4KiB mappings if the target gfn can just be mapped with a 2MiB hugepage x86 generic: - Copy single-chunk MMIO write values into struct kvm_vcpu (more precisely struct kvm_mmio_fragment) to fix use-after-free stack bugs where KVM would dereference stack pointer after an exit to userspace - Clean up and comment the emulated MMIO code to try to make it easier to maintain (not necessarily "easy", but "easier") - Move VMXON+VMXOFF and EFER.SVME toggling out of KVM (not *all* of VMX and SVM enabling) as it is needed for trusted I/O - Advertise support for AVX512 Bit Matrix Multiply (BMM) instructions - Immediately fail the build if a required #define is missing in one of KVM's headers that is included multiple times - Reject SET_GUEST_DEBUG with -EBUSY if there's an already injected exception, mostly to prevent syzkaller from abusing the uAPI to trigger WARNs, but also because it can help prevent userspace from unintentionally crashing the VM - Exempt SMM from CPUID faulting on Intel, as per the spec - Misc hardening and cleanup changes x86 (AMD): - Fix and optimize IRQ window inhibit handling for AVIC; make it per-vCPU so that KVM doesn't prematurely re-enable AVIC if multiple vCPUs have to-be-injected IRQs - Clean up and optimize the OSVW handling, avoiding a bug in which KVM would overwrite state when enabling virtualization on multiple CPUs in parallel. This should not be a problem because OSVW should usually be the same for all CPUs - Drop a WARN in KVM_MEMORY_ENCRYPT_REG_REGION where KVM complains about a "too large" size based purely on user input - Clean up and harden the pinning code for KVM_MEMORY_ENCRYPT_REG_REGION - Disallow synchronizing a VMSA of an already-launched/encrypted vCPU, as doing so for an SNP guest will crash the host due to an RMP violation page fault - Overhaul KVM's APIs for detecting SEV+ guests so that VM-scoped queries are required to hold kvm->lock, and enforce it by lockdep. Fix various bugs where sev_guest() was not ensured to be stable for the whole duration of a function or ioctl - Convert a pile of kvm->lock SEV code to guard() - Play nicer with userspace that does not enable KVM_CAP_EXCEPTION_PAYLOAD, for which KVM needs to set CR2 and DR6 as a response to ioctls such as KVM_GET_VCPU_EVENTS (even if the payload would end up in EXITINFO2 rather than CR2, for example). Only set CR2 and DR6 when consumption of the payload is imminent, but on the other hand force delivery of the payload in all paths where userspace retrieves CR2 or DR6 - Use vcpu->arch.cr2 when updating vmcb12's CR2 on nested #VMEXIT instead of vmcb02->save.cr2. The value is out of sync after a save/restore or after a #PF is injected into L2 - Fix a class of nSVM bugs where some fields written by the CPU are not synchronized from vmcb02 to cached vmcb12 after VMRUN, and so are not up-to-date when saved by KVM_GET_NESTED_STATE - Fix a class of bugs where the ordering between KVM_SET_NESTED_STATE and KVM_SET_{S}REGS could cause vmcb02 to be incorrectly initialized after save+restore - Add a variety of missing nSVM consistency checks - Fix several bugs where KVM failed to correctly update VMCB fields on nested #VMEXIT - Fix several bugs where KVM failed to correctly synthesize #UD or #GP for SVM-related instructions - Add support for save+restore of virtualized LBRs (on SVM) - Refactor various helpers and macros to improve clarity and (hopefully) make the code easier to maintain - Aggressively sanitize fields when copying from vmcb12, to guard against unintentionally allowing L1 to utilize yet-to-be-defined features - Fix several bugs where KVM botched rAX legality checks when emulating SVM instructions. There are remaining issues in that KVM doesn't handle size prefix overrides for 64-bit guests - Fail emulation of VMRUN/VMLOAD/VMSAVE if mapping vmcb12 fails instead of somewhat arbitrarily synthesizing #GP (i.e. don't double down on AMD's architectural but sketchy behavior of generating #GP for "unsupported" addresses) - Cache all used vmcb12 fields to further harden against TOCTOU bugs x86 (Intel): - Drop obsolete branch hint prefixes from the VMX instruction macros - Use ASM_INPUT_RM() in __vmcs_writel() to coerce clang into using a register input when appropriate - Code cleanups guest_memfd: - Don't mark guest_memfd folios as accessed, as guest_memfd doesn't support reclaim, the memory is unevictable, and there is no storage to write back to LoongArch selftests: - Add KVM PMU test cases s390 selftests: - Enable more memory selftests x86 selftests: - Add support for Hygon CPUs in KVM selftests - Fix a bug in the MSR test where it would get false failures on AMD/Hygon CPUs with exactly one of RDPID or RDTSCP - Add an MADV_COLLAPSE testcase for guest_memfd as a regression test for a bug where the kernel would attempt to collapse guest_memfd folios against KVM's will" * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (373 commits) KVM: x86: use inlines instead of macros for is_sev_*guest x86/virt: Treat SVM as unsupported when running as an SEV+ guest KVM: SEV: Goto an existing error label if charging misc_cg for an ASID fails KVM: SVM: Move lock-protected allocation of SEV ASID into a separate helper KVM: SEV: use mutex guard in snp_handle_guest_req() KVM: SEV: use mutex guard in sev_mem_enc_unregister_region() KVM: SEV: use mutex guard in sev_mem_enc_ioctl() KVM: SEV: use mutex guard in snp_launch_update() KVM: SEV: Assert that kvm->lock is held when querying SEV+ support KVM: SEV: Document that checking for SEV+ guests when reclaiming memory is "safe" KVM: SEV: Hide "struct kvm_sev_info" behind CONFIG_KVM_AMD_SEV=y KVM: SEV: WARN on unhandled VM type when initializing VM KVM: LoongArch: selftests: Add PMU overflow interrupt test KVM: LoongArch: selftests: Add basic PMU event counting test KVM: LoongArch: selftests: Add cpucfg read/write helpers LoongArch: KVM: Add DMSINTC inject msi to vCPU LoongArch: KVM: Add DMSINTC device support LoongArch: KVM: Make vcpu_is_preempted() as a macro rather than function LoongArch: KVM: Move host CSR_GSTAT save and restore in context switch LoongArch: KVM: Move host CSR_EENTRY save and restore in context switch ...

Merge tag 'kvm-x86-vmxon-7.1' of https://github.com/kvm-x86/linux into HEAD

2026-04-13T11:04:48+00:00

KVM x86 VMXON and EFER.SVME extraction for 7.1 Move _only_ VMXON+VMXOFF and EFER.SVME toggling out of KVM (versus all of VMX and SVM enabling) out of KVM and into the core kernel so that non-KVM TDX enabling, e.g. for trusted I/O, can make SEAMCALLs without needing to ensure KVM is fully loaded. TIO isn't a hypervisor, and isn't trying to be a hypervisor. Specifically, TIO should _never_ have it's own VMCSes (that are visible to the host; the TDX-Module has it's own VMCSes to do SEAMCALL/SEAMRET), and so there is simply no reason to move that functionality out of KVM. With that out of the way, dealing with VMXON/VMXOFF and EFER.SVME is a fairly simple refcounting game.

Merge tag 'kvm-x86-misc-7.1' of https://github.com/kvm-x86/linux into HEAD

2026-04-13T09:51:34+00:00

KVM x86 misc changes for 7.1 - Advertise support for AVX512 Bit Matrix Multiply (BMM) when it's present in hardware (no additional emulation/virtualization required). - Immediately fail the build if a required #define is missing in one of KVM's headers that is included multiple times. - Reject SET_GUEST_DEBUG with -EBUSY if there's an already injected exception, mostly to prevent syzkaller from abusing the uAPI to trigger WARNs, but also because it can help prevent userspace from unintentionally crashing the VM. - Exempt SMM from CPUID faulting on Intel, as per the spec. - Misc hardening and cleanup changes.

mm: change to return bool for the MMU notifier's young flag check

2026-04-05T20:53:35+00:00

The MMU notifier young flag check related functions only return whether the young flag was set. Change the return type to bool to make the intention clearer. Link: https://lkml.kernel.org/r/a9ad3fe938002d87358e7bfca264f753ab602561.1774075004.git.baolin.wang@linux.alibaba.com Signed-off-by: Baolin Wang Reviewed-by: Lorenzo Stoakes (Oracle) Acked-by: David Hildenbrand (Arm) Cc: Liam Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: Ritesh Harjani (IBM) Cc: Suren Baghdasaryan Signed-off-by: Andrew Morton

KVM: remove hugetlb.h inclusion

2026-04-05T20:53:23+00:00

hugetlb.h is no longer required now that we moved vma_kernel_pagesize() to mm.h. Link: https://lkml.kernel.org/r/20260309151901.123947-4-david@kernel.org Signed-off-by: David Hildenbrand (Arm) Reviewed-by: Lorenzo Stoakes (Oracle) Acked-by: Mike Rapoport (Microsoft) Cc: "Christophe Leroy (CS GROUP)" Cc: Dan Williams Cc: Jann Horn Cc: Liam Howlett Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Michal Hocko Cc: Muchun Song Cc: Nicholas Piggin Cc: Oscar Salvador Cc: Paolo Bonzini Cc: Pedro Falcato Cc: Suren Baghdasaryan Signed-off-by: Andrew Morton

Merge tag 'kvm-x86-generic-7.0-rc3' of https://github.com/kvm-x86/linux into HEAD

2026-03-11T17:01:55+00:00

KVM generic changes for 7.0 - Remove a subtle pseudo-overlay of kvm_stats_desc, which, aside from being unnecessary and confusing, triggered compiler warnings due to -Wflex-array-member-not-at-end. - Document that vcpu->mutex is take outside of kvm->slots_lock and kvm->slots_arch_lock, which is intentional and desirable despite being rather unintuitive.

KVM: Bury kvm_{en,dis}able_virtualization() in kvm_main.c once more

2026-03-04T16:53:10+00:00

Now that TDX handles doing VMXON without KVM's involvement, bury the top-level APIs to enable and disable virtualization back in kvm_main.c. No functional change intended. Reviewed-by: Dan Williams Reviewed-by: Chao Gao Tested-by: Chao Gao Tested-by: Sagi Shahar Link: https://patch.msgid.link/20260214012702.2368778-16-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: x86: Move kvm_rebooting to x86

2026-03-04T16:52:19+00:00

Move kvm_rebooting, which is only read by x86, to KVM x86 so that it can be moved again to core x86 code. Add a "shutdown" arch hook to facilate setting the flag in KVM x86, along with a pile of comments to provide more context around what KVM x86 is doing and why. Reviewed-by: Chao Gao Acked-by: Dave Hansen Tested-by: Chao Gao Reviewed-by: Dan Williams Tested-by: Sagi Shahar Link: https://patch.msgid.link/20260214012702.2368778-2-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: Mark halt poll and other module parameters with appropriate memory attributes

2026-03-02T22:32:29+00:00

Add '__read_mostly' to the halt polling parameters (halt_poll_ns, halt_poll_ns_grow, halt_poll_ns_grow_start, halt_poll_ns_shrink) since they are frequently read in hot paths (e.g., vCPU halt handling) but only occasionally updated via sysfs. This improves cache locality on SMP systems. Conversely, mark 'allow_unsafe_mappings' and 'enable_virt_at_load' with '__ro_after_init', as they are set only during module initialization via kernel command line or early sysfs writes and remain constant thereafter. This enhances security by preventing runtime modification and enables compiler optimizations. Signed-off-by: Li RongQing Link: https://patch.msgid.link/20260210062143.1739-1-lirongqing@baidu.com Signed-off-by: Sean Christopherson