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Message-ID: <CABgObfZ4QhxnkT4vuzeayor4rpRU9yQVejiEPe6wGFTOt9F+Wg@mail.gmail.com>
Date: Wed, 26 Nov 2025 09:49:30 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] KVM: x86: Misc changes for 6.19
On Wed, Nov 26, 2025 at 2:45 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> The bulk of the vendor agnostic x86 changes for 6.19. There are multiple
> noteworthy changes, though nothing stands out as being _that_ much more
> interesting than the rest.
>
> The following changes since commit 211ddde0823f1442e4ad052a2f30f050145ccada:
>
> Linux 6.18-rc2 (2025-10-19 15:19:16 -1000)
>
> are available in the Git repository at:
>
> https://github.com/kvm-x86/linux.git tags/kvm-x86-misc-6.19
>
> for you to fetch changes up to c09816f2afce0f89f176c4bc58dc57ec9f204998:
>
> KVM: x86: Remove unused declaration kvm_mmu_may_ignore_guest_pat() (2025-11-20 07:26:35 -0800)
Pulled, thanks.
Paolo
> ----------------------------------------------------------------
> KVM x86 misc changes for 6.19:
>
> - Fix an async #PF bug where KVM would clear the completion queue when the
> guest transitioned in and out of paging mode, e.g. when handling an SMI and
> then returning to paged mode via RSM.
>
> - Fix a bug where TDX would effectively corrupt user-return MSR values if the
> TDX Module rejects VP.ENTER and thus doesn't clobber host MSRs as expected.
>
> - Leave the user-return notifier used to restore MSRs registered when
> disabling virtualization, and instead pin kvm.ko. Restoring host MSRs via
> IPI callback is either pointless (clean reboot) or dangerous (forced reboot)
> since KVM has no idea what code it's interrupting.
>
> - Use the checked version of {get,put}_user(), as Linus wants to kill them
> off, and they're measurably faster on modern CPUs due to the unchecked
> versions containing an LFENCE.
>
> - Fix a long-lurking bug where KVM's lack of catch-up logic for periodic APIC
> timers can result in a hard lockup in the host.
>
> - Revert the periodic kvmclock sync logic now that KVM doesn't use a
> clocksource that's subject to NPT corrections.
>
> - Clean up KVM's handling of MMIO Stale Data and L1TF, and bury the latter
> behind CONFIG_CPU_MITIGATIONS.
>
> - Context switch XCR0, XSS, and PKRU outside of the entry/exit fastpath as
> the only reason they were handled in the faspath was to paper of a bug in
> the core #MC code that has long since been fixed.
>
> - Add emulator support for AVX MOV instructions to play nice with emulated
> devices whose PCI BARs guest drivers like to access with large multi-byte
> instructions.
>
> ----------------------------------------------------------------
> Binbin Wu (1):
> KVM: x86: Add a helper to dedup loading guest/host XCR0 and XSS
>
> Brendan Jackman (1):
> KVM: x86: Unify L1TF flushing under per-CPU variable
>
> Chang S. Bae (1):
> KVM: x86: Refactor REX prefix handling in instruction emulation
>
> Chao Gao (1):
> KVM: x86: Allocate/free user_return_msrs at kvm.ko (un)loading time
>
> Hou Wenlong (1):
> KVM: x86: Don't disable IRQs when unregistering user-return notifier
>
> Lei Chen (3):
> Revert "x86: kvm: introduce periodic global clock updates"
> Revert "x86: kvm: rate-limit global clock updates"
> KVM: x86: remove comment about ntp correction sync for
>
> Maxim Levitsky (2):
> KVM: x86: Fix a semi theoretical bug in kvm_arch_async_page_present_queued()
> KVM: x86: Don't clear async #PF queue when CR0.PG is disabled (e.g. on #SMI)
>
> Paolo Bonzini (9):
> KVM: x86: Add support for emulating MOVNTDQA
> KVM: x86: Move Src2Shift up one bit (use bits 36:32 for Src2 in the emulator)
> KVM: x86: Improve formatting of the emulator's flags table
> KVM: x86: Move op_prefix to struct x86_emulate_ctxt (from x86_decode_insn())
> KVM: x86: Share emulator's common register decoding code
> KVM: x86: Add x86_emulate_ops.get_xcr() callback
> KVM: x86: Add AVX support to the emulator's register fetch and writeback
> KVM: x86: Add emulator support for decoding VEX prefixes
> KVM: x86: Enable support for emulating AVX MOV instructions
>
> Pawan Gupta (1):
> x86/bugs: Use VM_CLEAR_CPU_BUFFERS in VMX as well
>
> Sean Christopherson (18):
> KVM: x86: Add a helper to dedup reporting of unhandled VM-Exits
> KVM: TDX: Explicitly set user-return MSRs that *may* be clobbered by the TDX-Module
> KVM: x86: WARN if user-return MSR notifier is registered on exit
> KVM: x86: Leave user-return notifier registered on reboot/shutdown
> KVM: x86: Use "checked" versions of get_user() and put_user()
> KVM: x86: WARN if hrtimer callback for periodic APIC timer fires with period=0
> KVM: x86: Grab lapic_timer in a local variable to cleanup periodic code
> KVM: VMX: Use on-stack copy of @flags in __vmx_vcpu_run()
> x86/bugs: Decouple ALTERNATIVE usage from VERW macro definition
> x86/bugs: Use an x86 feature to track the MMIO Stale Data mitigation
> KVM: VMX: Handle MMIO Stale Data in VM-Enter assembly via ALTERNATIVES_2
> x86/bugs: KVM: Move VM_CLEAR_CPU_BUFFERS into SVM as SVM_CLEAR_CPU_BUFFERS
> KVM: VMX: Bundle all L1 data cache flush mitigation code together
> KVM: VMX: Disable L1TF L1 data cache flush if CONFIG_CPU_MITIGATIONS=n
> KVM: SVM: Handle #MCs in guest outside of fastpath
> KVM: VMX: Handle #MCs on VM-Enter/TD-Enter outside of the fastpath
> KVM: x86: Load guest/host XCR0 and XSS outside of the fastpath run loop
> KVM: x86: Load guest/host PKRU outside of the fastpath run loop
>
> Yue Haibing (1):
> KVM: x86: Remove unused declaration kvm_mmu_may_ignore_guest_pat()
>
> fuqiang wang (2):
> KVM: x86: Explicitly set new periodic hrtimer expiration in apic_timer_fn()
> KVM: x86: Fix VM hard lockup after prolonged inactivity with periodic HV timer
>
> arch/x86/include/asm/cpufeatures.h | 5 ++
> arch/x86/include/asm/hardirq.h | 4 +-
> arch/x86/include/asm/kvm_host.h | 7 +--
> arch/x86/include/asm/nospec-branch.h | 30 ++++++------
> arch/x86/kernel/cpu/bugs.c | 22 ++++-----
> arch/x86/kvm/emulate.c | 319 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------------------------
> arch/x86/kvm/fpu.h | 66 +++++++++++++++++++++++++++
> arch/x86/kvm/hyperv.c | 2 +-
> arch/x86/kvm/kvm_emulate.h | 20 ++++++--
> arch/x86/kvm/lapic.c | 44 ++++++++++++------
> arch/x86/kvm/mmu.h | 2 -
> arch/x86/kvm/mmu/mmu.c | 2 +-
> arch/x86/kvm/mmu/paging_tmpl.h | 2 +-
> arch/x86/kvm/mmu/spte.c | 2 +-
> arch/x86/kvm/svm/svm.c | 27 ++++-------
> arch/x86/kvm/svm/vmenter.S | 6 ++-
> arch/x86/kvm/vmx/nested.c | 2 +-
> arch/x86/kvm/vmx/run_flags.h | 10 ++--
> arch/x86/kvm/vmx/tdx.c | 65 ++++++++++----------------
> arch/x86/kvm/vmx/tdx.h | 1 -
> arch/x86/kvm/vmx/vmenter.S | 29 +++++++-----
> arch/x86/kvm/vmx/vmx.c | 264 ++++++++++++++++++++++++++++++++++++++++++++++++++++++----------------------------------------------------
> arch/x86/kvm/x86.c | 259 +++++++++++++++++++++++++++++++++++++++++++++++++++-----------------------------------------------------
> arch/x86/kvm/x86.h | 16 ++++++-
> 24 files changed, 706 insertions(+), 500 deletions(-)
>
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