KVM: vmx/pmu: Reduce the overhead of LBR pass-through or cancellation

When the LBR records msrs has already been pass-through, there is no
need to call vmx_update_intercept_for_lbr_msrs() again and again, and
vice versa.
Signed-off-by: Like Xu <like.xu@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Message-Id: <20210201051039.255478-8-like.xu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/pmu_intel.c

@@ -557,6 +557,7 @@ static void intel_pmu_init(struct kvm_vcpu *vcpu)
 	vcpu->arch.perf_capabilities = vmx_get_perf_capabilities();
 	lbr_desc->records.nr = 0;
 	lbr_desc->event = NULL;
+	lbr_desc->msr_passthrough = false;
 }
 
 static void intel_pmu_reset(struct kvm_vcpu *vcpu)
@@ -603,12 +604,24 @@ static void vmx_update_intercept_for_lbr_msrs(struct kvm_vcpu *vcpu, bool set)
 
 static inline void vmx_disable_lbr_msrs_passthrough(struct kvm_vcpu *vcpu)
 {
+	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
+
+	if (!lbr_desc->msr_passthrough)
+		return;
+
 	vmx_update_intercept_for_lbr_msrs(vcpu, true);
+	lbr_desc->msr_passthrough = false;
 }
 
 static inline void vmx_enable_lbr_msrs_passthrough(struct kvm_vcpu *vcpu)
 {
+	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
+
+	if (lbr_desc->msr_passthrough)
+		return;
+
 	vmx_update_intercept_for_lbr_msrs(vcpu, false);
+	lbr_desc->msr_passthrough = true;
 }
 
 /*

arch/x86/kvm/vmx/vmx.h

@@ -113,6 +113,9 @@ struct lbr_desc {
 	 * The records may be inaccurate if the host reclaims the LBR.
 	 */
 	struct perf_event *event;
+
+	/* True if LBRs are marked as not intercepted in the MSR bitmap */
+	bool msr_passthrough;
 };
 
 /*