KVM: VMX: Disable LBR virtualization if the CPU doesn't support LBR callstacks

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Disable LBR virtualization if the CPU doesn't support callstacks, which
were introduced in HSW (see commit e9d7f7cd97 ("perf/x86/intel: Add
basic Haswell LBR call stack support"), as KVM unconditionally configures
the perf LBR event with PERF_SAMPLE_BRANCH_CALL_STACK, i.e. LBR
virtualization always fails on pre-HSW CPUs.

Simply disable LBR support on such CPUs, as it has never worked, i.e.
there is no risk of breaking an existing setup, and figuring out a way
to performantly context switch LBRs on old CPUs is not worth the effort.

Fixes: be635e34c2 ("KVM: vmx/pmu: Expose LBR_FMT in the MSR_IA32_PERF_CAPABILITIES")
Cc: Mingwei Zhang <mizhang@google.com>
Cc: Jim Mattson <jmattson@google.com>
Tested-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20240307011344.835640-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

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Sean Christopherson 2024-03-06 17:13:44 -08:00

parent 0d0b608650

commit bb9dc85908

1 changed files with 9 additions and 1 deletions

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arch/x86/kvm/vmx/vmx.c

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