linux-kernel - Re: [PATCH 0/6] KVM: SVM: LBR virtualization fixes

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Message-ID: <35d28432-349c-4157-8c9e-7d4a9d8bd50f@redhat.com>
Date: Sun, 9 Nov 2025 08:57:20 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>,
 Sean Christopherson <seanjc@...gle.com>
Cc: Jim Mattson <jmattson@...gle.com>, Maxim Levitsky <mlevitsk@...hat.com>,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] KVM: SVM: LBR virtualization fixes

On 11/8/25 01:45, Yosry Ahmed wrote:
> This series fixes multiple problems with LBR virtualization, including a
> fun problem that leads to L1 reading the host's LBR MSRs. It also
> considerably simplifies the code.
> 
> The series has a selftest in the end that verifies that save/restore
> work correctly. I will send a couple of new kvm-unit-tests separately
> that exercise the bugs fixed by patches 2 & 3.

Thanks, I've applied patches 1-3 for now.

Save/restore has been broken for 17 years so it can wait the next 
release anyway. :)

Paolo

> 
> Yosry Ahmed (6):
>    KVM: SVM: Mark VMCB_LBR dirty when MSR_IA32_DEBUGCTLMSR is updated
>    KVM: nSVM: Always recalculate LBR MSR intercepts in svm_update_lbrv()
>    KVM: nSVM: Fix and simplify LBR virtualization handling with nested
>    KVM: SVM: Switch svm_copy_lbrs() to a macro
>    KVM: SVM: Add missing save/restore handling of LBR MSRs
>    KVM: selftests: Add a test for LBR save/restore (ft. nested)
> 
>   arch/x86/kvm/svm/nested.c                     |  31 ++--
>   arch/x86/kvm/svm/svm.c                        |  98 ++++++-----
>   arch/x86/kvm/svm/svm.h                        |  10 +-
>   arch/x86/kvm/x86.c                            |   3 +
>   tools/testing/selftests/kvm/Makefile.kvm      |   1 +
>   .../selftests/kvm/include/x86/processor.h     |   5 +
>   .../selftests/kvm/x86/svm_lbr_nested_state.c  | 155 ++++++++++++++++++
>   7 files changed, 236 insertions(+), 67 deletions(-)
>   create mode 100644 tools/testing/selftests/kvm/x86/svm_lbr_nested_state.c
>