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Date:   Fri,  8 Jan 2021 09:37:01 +0800
From:   Like Xu <like.xu@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, ak@...ux.intel.com,
        wei.w.wang@...el.com, kan.liang@...el.com, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RESEND v13 07/10] 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@...ux.intel.com>
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/kvm/vmx/pmu_intel.c | 13 +++++++++++++
 arch/x86/kvm/vmx/vmx.h       |  3 +++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 6b3319dbfa72..72a6dd6ca0ac 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -562,6 +562,7 @@ static void intel_pmu_init(struct kvm_vcpu *vcpu)
 		vmx_get_perf_capabilities() : 0;
 	lbr_desc->records.nr = 0;
 	lbr_desc->event = NULL;
+	lbr_desc->already_passthrough = false;
 }
 
 static void intel_pmu_reset(struct kvm_vcpu *vcpu)
@@ -607,12 +608,24 @@ 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->already_passthrough)
+		return;
+
 	vmx_update_intercept_for_lbr_msrs(vcpu, true);
+	lbr_desc->already_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->already_passthrough)
+		return;
+
 	vmx_update_intercept_for_lbr_msrs(vcpu, false);
+	lbr_desc->already_passthrough = true;
 }
 
 /*
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 863bb3fe73d4..b79244bd44bb 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -90,6 +90,9 @@ struct lbr_desc {
 	 * The records may be inaccurate if the host reclaims the LBR.
 	 */
 	struct perf_event *event;
+
+	/* A flag to reduce the overhead of LBR pass-through or cancellation. */
+	bool already_passthrough;
 };
 
 /*
-- 
2.29.2

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