KVM: SVM: LBR virtualization fixes

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

Posted by Yosry Ahmed 1 month, 1 week ago

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.

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

-- 
2.51.2.1041.gc1ab5b90ca-goog

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

Posted by Paolo Bonzini 1 month, 1 week ago

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
>