Messages in this thread | | | Date | Tue, 2 Aug 2022 20:04:53 +0800 | Subject | Re: [PATCH 3/3] KVM: VMX: Adjust number of LBR records for PERF_CAPABILITIES at refresh | From | Like Xu <> |
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On 28/7/2022 7:34 am, Sean Christopherson wrote: > -bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu) > -{ > - struct x86_pmu_lbr *lbr = vcpu_to_lbr_records(vcpu); > - > - return lbr->nr && (vcpu_get_perf_capabilities(vcpu) & PMU_CAP_LBR_FMT); > -} > - > static bool intel_pmu_is_valid_lbr_msr(struct kvm_vcpu *vcpu, u32 index) > { > struct x86_pmu_lbr *records = vcpu_to_lbr_records(vcpu); > @@ -590,7 +583,9 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu) > bitmap_set(pmu->all_valid_pmc_idx, > INTEL_PMC_MAX_GENERIC, pmu->nr_arch_fixed_counters); > > - if (cpuid_model_is_consistent(vcpu)) > + perf_capabilities = vcpu_get_perf_capabilities(vcpu); > + if (cpuid_model_is_consistent(vcpu) && > + (perf_capabilities & PMU_CAP_LBR_FMT)) > x86_perf_get_lbr(&lbr_desc->records);
As one of evil source to add CPUID walk in the critical path:
The x86_perf_get_lbr() is one of the perf interfaces, KVM cannot always trust that the number of returned lbr_desc->records.nr is always > 0, and if not, we have to tweak perf_capabilities inside KVM which violates user input again.
Do you have more inputs to address this issue ?
> else > lbr_desc->records.nr = 0;
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