Re: [PATCH 0/3] KVM: VMX: Disable LBRs if CPU doesn't have callstacks

Sean Christopherson
2024-04-09T02:02:58Z

On Wed, 06 Mar 2024 17:13:41 -0800, Sean Christopherson wrote:
> Disable LBR virtualization if the CPU (or I guess perf) doesn't support
> LBR callstacks, as KVM unconditionally creates the associated perf LBR
> event with PERF_SAMPLE_BRANCH_CALL_STACK. That results in perf rejecting
> the event, and cause LBR virtualization to silently fail.
>
> This was detected by running vmx_pmu_caps_test on older hardware. I didn't
> tag it for stable because I can't imagine anyone is trying to use KVM's LBR
> virtualization on pre-HSW.
>
> [...]

Applied to kvm-x86 fixes, as I can't imagine anyone objecting to patch 2.

[1/3] KVM: VMX: Snapshot LBR capabilities during module initialization
https://github.com/kvm-x86/linux/commit/2a94a2761236
[2/3] perf/x86/intel: Expose existence of callback support to KVM
https://github.com/kvm-x86/linux/commit/0c0241c12332
[3/3] KVM: VMX: Disable LBR virtualization if the CPU doesn't support LBR callstacks
https://github.com/kvm-x86/linux/commit/0eb2416c8111

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