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| author | Sean Christopherson <seanjc@google.com> | 2024-03-06 17:13:44 -0800 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2024-04-11 12:58:48 -0700 |
| commit | bb9dc859086df369f1fd34578dd5ca82d6321d21 (patch) | |
| tree | 77059541a6045d0464d259e40235e3c9acbe2557 /arch | |
| parent | 0d0b60865071115f6da76090f0dbc1f0e8b9c647 (diff) | |
| download | linux-stable-bb9dc859086df369f1fd34578dd5ca82d6321d21.tar.gz linux-stable-bb9dc859086df369f1fd34578dd5ca82d6321d21.tar.bz2 linux-stable-bb9dc859086df369f1fd34578dd5ca82d6321d21.zip | |
KVM: VMX: Disable LBR virtualization if the CPU doesn't support LBR callstacks
Disable LBR virtualization if the CPU doesn't support callstacks, which
were introduced in HSW (see commit e9d7f7cd97c4 ("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: be635e34c284 ("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>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/vmx/vmx.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index aca41d3419f9..22411f4aff53 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7877,7 +7877,15 @@ static __init u64 vmx_get_perf_capabilities(void) if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR)) { x86_perf_get_lbr(&vmx_lbr_caps); - if (vmx_lbr_caps.nr) + + /* + * KVM requires LBR callstack support, as the overhead due to + * context switching LBRs without said support is too high. + * See intel_pmu_create_guest_lbr_event() for more info. + */ + if (!vmx_lbr_caps.has_callstack) + memset(&vmx_lbr_caps, 0, sizeof(vmx_lbr_caps)); + else if (vmx_lbr_caps.nr) perf_cap |= host_perf_cap & PMU_CAP_LBR_FMT; } |