kernel/linux.git/Documentation/virt/kvm, branch v7.0-rc7

Documentation: kvm: fix formatting of the quirks table

2026-03-11T18:16:52+00:00

A recently added quirk does not fit in the left column of the table, so it all has to be reformatted and realigned. Signed-off-by: Paolo Bonzini

KVM: x86: Introduce KVM_X86_QUIRK_VMCS12_ALLOW_FREEZE_IN_SMM

2026-03-11T17:41:11+00:00

Add KVM_X86_QUIRK_VMCS12_ALLOW_FREEZE_IN_SMM to allow L1 to set FREEZE_IN_SMM in vmcs12's GUEST_IA32_DEBUGCTL field, as permitted prior to commit 6b1dd26544d0 ("KVM: VMX: Preserve host's DEBUGCTLMSR_FREEZE_IN_SMM while running the guest"). Enable the quirk by default for backwards compatibility (like all quirks); userspace can disable it via KVM_CAP_DISABLE_QUIRKS2 for consistency with the constraints on WRMSR(IA32_DEBUGCTL). Note that the quirk only bypasses the consistency check. The vmcs02 bit is still owned by the host, and PMCs are not frozen during virtualized SMM. In particular, if a host administrator decides that PMCs should not be frozen during physical SMM, then L1 has no say in the matter. Fixes: 095686e6fcb4 ("KVM: nVMX: Check vmcs12->guest_ia32_debugctl on nested VM-Enter") Cc: stable@vger.kernel.org Signed-off-by: Jim Mattson Link: https://patch.msgid.link/20260205231537.1278753-1-jmattson@google.com [sean: tag for stable@, clean-up and fix goofs in the comment and docs] Signed-off-by: Sean Christopherson [Rename quirk. - Paolo] Signed-off-by: Paolo Bonzini

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.

Documentation: KVM: Formalizing taking vcpu->mutex outside of kvm->slots_lock

2026-03-02T17:52:09+00:00

Explicitly document the ordering of vcpu->mutex being taken *outside* of kvm->slots_lock. While somewhat unintuitive since vCPUs conceptually have narrower scope than VMs, the scope of the owning object (vCPU versus VM) doesn't automatically carry over to the lock. In this case, vcpu->mutex has far broader scope than kvm->slots_lock. As Paolo put it, it's a "don't worry about multiple ioctls at the same time" mutex that's intended to be taken at the outer edges of KVM. More importantly, arm64 and x86 have gained flows that take kvm->slots_lock inside of vcpu->mutex. x86's kvm_inhibit_apic_access_page() is particularly nasty, as slots_lock is taken quite deep within KVM_RUN, i.e. simply swapping the ordering isn't an option. Commit to the vcpu->mutex => kvm->slots_lock ordering, as vcpu->mutex really is intended to be a "top-level" lock, whereas kvm->slots_lock is "just" a helper lock. Opportunistically document that vcpu->mutex is also taken outside of slots_arch_lock, e.g. when allocating shadow roots on x86 (which is the entire reason slots_arch_lock exists, as shadow roots must be allocated while holding kvm->srcu) kvm_mmu_new_pgd() | -> kvm_mmu_reload() | -> kvm_mmu_load() | -> mmu_alloc_shadow_roots() | -> mmu_first_shadow_root_alloc() but also when manipulating memslots in vCPU context, e.g. when inhibiting the APIC-access page via the aforementioned kvm_inhibit_apic_access_page() kvm_inhibit_apic_access_page() | -> __x86_set_memory_region() | -> kvm_set_internal_memslot() | -> kvm_set_memory_region() | -> kvm_set_memslot() Cc: Oliver Upton Cc: Marc Zyngier Link: https://patch.msgid.link/20260302170239.596810-1-seanjc@google.com Signed-off-by: Sean Christopherson

KVM: always define KVM_CAP_SYNC_MMU

2026-02-28T14:31:35+00:00

KVM_CAP_SYNC_MMU is provided by KVM's MMU notifiers, which are now always available. Move the definition from individual architectures to common code. Signed-off-by: Paolo Bonzini

Merge tag 'kvm-s390-next-7.0-1' of https://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into HEAD

2026-02-11T17:52:27+00:00

- gmap rewrite: completely new memory management for kvm/s390 - vSIE improvement - maintainership change for s390 vfio-pci - small quality of life improvement for protected guests

Merge tag 'kvm-x86-gmem-6.20' of https://github.com/kvm-x86/linux into HEAD

2026-02-11T17:45:12+00:00

KVM guest_memfd changes for 6.20 - Remove kvm_gmem_populate()'s preparation tracking and half-baked hugepage handling, and instead rely on SNP (the only user of the tracking) to do its own tracking via the RMP. - Retroactively document and enforce (for SNP) that KVM_SEV_SNP_LAUNCH_UPDATE and KVM_TDX_INIT_MEM_REGION require the source page to be 4KiB aligned, to avoid non-trivial complexity for a non-existent usecase (and because in-place conversion simply can't support unaligned sources). - When populating guest_memfd memory, GUP the source page in common code and pass the refcounted page to the vendor callback, instead of letting vendor code do the heavy lifting. Doing so avoids a looming deadlock bug with in-place due an AB-BA conflict betwee mmap_lock and guest_memfd's filemap invalidate lock.

Merge tag 'kvm-x86-misc-6.20' of https://github.com/kvm-x86/linux into HEAD

2026-02-09T17:53:47+00:00

KVM x86 misc changes for 6.20 - Disallow changing the virtual CPU model if L2 is active, for all the same reasons KVM disallows change the model after the first KVM_RUN. - Fix a bug where KVM would incorrectly reject host accesses to PV MSRs that were advertised as supported to userspace when running with KVM_CAP_ENFORCE_PV_FEATURE_CPUID enabled. - Fix a bug where KVM would attempt to read protect guest state (CR3) when configuring an async #PF entry. - Fail the build if EXPORT_SYMBOL_GPL or EXPORT_SYMBOL is used in KVM (for x86 only) to enforce usage of EXPORT_SYMBOL_FOR_KVM_INTERNAL. Explicitly allow the few exports that are intended for external usage. - Ignore -EBUSY when checking nested events after a vCPU exits blocking as the WARN is user-triggerable, and because exiting to userspace on -EBUSY does more harm than good in pretty much every situation. - Throw in the towel and drop the WARN on INIT/SIPI being blocked when vCPU is in Wait-For-SIPI, as playing whack-a-mole with syzkaller turned out to be an unwinnable game. - Add support for new Intel instructions that don't require anything beyond enumerating feature flags to userspace. - Grab SRCU when reading PDPTRs in KVM_GET_SREGS2. - Add WARNs to guard against modifying KVM's CPU caps outside of the intended setup flow, as nested VMX in particular is sensitive to unexpected changes in KVM's golden configuration. - Add a quirk to allow userspace to opt-in to actually suppress EOI broadcasts when the suppression feature is enabled by the guest (currently limited to split IRQCHIP, i.e. userspace I/O APIC). Sadly, simply fixing KVM to honor Suppress EOI Broadcasts isn't an option as some userspaces have come to rely on KVM's buggy behavior (KVM advertises Supress EOI Broadcast irrespective of whether or not userspace I/O APIC supports Directed EOIs). - Minor cleanups.

Merge tag 'kvm-x86-svm-6.20' of https://github.com/kvm-x86/linux into HEAD

2026-02-09T17:51:37+00:00

KVM SVM changes for 6.20 - Drop a user-triggerable WARN on nested_svm_load_cr3() failure. - Add support for virtualizing ERAPS. Note, correct virtualization of ERAPS relies on an upcoming, publicly announced change in the APM to reduce the set of conditions where hardware (i.e. KVM) *must* flush the RAP. - Ignore nSVM intercepts for instructions that are not supported according to L1's virtual CPU model. - Add support for expedited writes to the fast MMIO bus, a la VMX's fastpath for EPT Misconfig. - Don't set GIF when clearing EFER.SVME, as GIF exists independently of SVM, and allow userspace to restore nested state with GIF=0. - Treat exit_code as an unsigned 64-bit value through all of KVM. - Add support for fetching SNP certificates from userspace. - Fix a bug where KVM would use vmcb02 instead of vmcb01 when emulating VMLOAD or VMSAVE on behalf of L2. - Misc fixes and cleanups.

KVM: s390: Storage key manipulation IOCTL

2026-02-04T16:00:10+00:00

Add a new IOCTL to allow userspace to manipulate storage keys directly. This will make it easier to write selftests related to storage keys. Acked-by: Heiko Carstens Signed-off-by: Claudio Imbrenda