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

Paolo Bonzini
2025-11-09T07:57:26Z

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
>