linux-kernel - [PATCH 3/3] KVM: VMX: Adjust number of LBR records for PERF

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Date:   Wed, 27 Jul 2022 23:34:24 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Like Xu <like.xu.linux@...il.com>
Subject: [PATCH 3/3] KVM: VMX: Adjust number of LBR records for
 PERF_CAPABILITIES at refresh

Now that the PMU is refreshed when MSR_IA32_PERF_CAPABILITIES is written
by host userspace, zero out the number of LBR records for a vCPU during
PMU refresh if PMU_CAP_LBR_FMT is not set in PERF_CAPABILITIES instead of
handling the check at run-time.

guest_cpuid_has() is expensive due to the linear search of guest CPUID
entries, intel_pmu_lbr_is_enabled() is checked on every VM-Enter, _and_
simply enumerating the same "Model" as the host causes KVM to set the
number of LBR records to a non-zero value.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/pmu_intel.c | 12 +++---------
 arch/x86/kvm/vmx/vmx.h       |  7 +++++--
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index cfcb590afaa7..d111dc0d86df 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -171,13 +171,6 @@ static inline struct kvm_pmc *get_fw_gp_pmc(struct kvm_pmu *pmu, u32 msr)
 	return get_gp_pmc(pmu, msr, MSR_IA32_PMC0);
 }
 
-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);
 	else
 		lbr_desc->records.nr = 0;
@@ -598,7 +593,6 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu)
 	if (lbr_desc->records.nr)
 		bitmap_set(pmu->all_valid_pmc_idx, INTEL_PMC_IDX_FIXED_VLBR, 1);
 
-	perf_capabilities = vcpu_get_perf_capabilities(vcpu);
 	if (perf_capabilities & PERF_CAP_PEBS_FORMAT) {
 		if (perf_capabilities & PERF_CAP_PEBS_BASELINE) {
 			pmu->pebs_enable_mask = counter_mask;
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 690421b7d26c..c05e302fe2b1 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -526,9 +526,12 @@ static inline struct x86_pmu_lbr *vcpu_to_lbr_records(struct kvm_vcpu *vcpu)
 	return &vcpu_to_lbr_desc(vcpu)->records;
 }
 
+static inline bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu)
+{
+	return !!vcpu_to_lbr_records(vcpu)->nr;
+}
+
 void intel_pmu_cross_mapped_check(struct kvm_pmu *pmu);
-bool intel_pmu_lbr_is_enabled(struct kvm_vcpu *vcpu);
-
 int intel_pmu_create_guest_lbr_event(struct kvm_vcpu *vcpu);
 void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu);
 
-- 
2.37.1.359.gd136c6c3e2-goog