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From:   Like Xu <like.xu@linux.intel.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, ak@linux.intel.com,
        wei.w.wang@intel.com, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, Like Xu <like.xu@linux.intel.com>
Subject: [PATCH v12 10/11] KVM: vmx/pmu: Reduce the overhead of LBR pass-through or cancellation
Date:   Sat, 13 Jun 2020 16:09:55 +0800
Message-Id: <20200613080958.132489-11-like.xu@linux.intel.com>
In-Reply-To: <20200613080958.132489-1-like.xu@linux.intel.com>
References: <20200613080958.132489-1-like.xu@linux.intel.com>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

When the LBR record 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>
---
 arch/x86/kvm/vmx/pmu_intel.c |  1 +
 arch/x86/kvm/vmx/vmx.c       | 12 ++++++++++++
 arch/x86/kvm/vmx/vmx.h       |  3 +++
 3 files changed, 16 insertions(+)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 85a675004cbb..75ba0444b4d1 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -614,6 +614,7 @@ static void intel_pmu_init(struct kvm_vcpu *vcpu)
 		vmx_get_perf_capabilities() : 0;
 	lbr_desc->lbr.nr = 0;
 	lbr_desc->event = NULL;
+	lbr_desc->already_passthrough = false;
 }
 
 static void intel_pmu_reset(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 58a8af433741..800a26e3b571 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3880,12 +3880,24 @@ static void vmx_update_intercept_for_lbr_msrs(struct kvm_vcpu *vcpu, bool set)
 
 static inline void vmx_lbr_disable_passthrough(struct kvm_vcpu *vcpu)
 {
+	struct lbr_desc *lbr_desc = &to_vmx(vcpu)->lbr_desc;
+
+	if (!lbr_desc->already_passthrough)
+		return;
+
 	vmx_update_intercept_for_lbr_msrs(vcpu, true);
+	lbr_desc->already_passthrough = false;
 }
 
 static inline void vmx_lbr_enable_passthrough(struct kvm_vcpu *vcpu)
 {
+	struct lbr_desc *lbr_desc = &to_vmx(vcpu)->lbr_desc;
+
+	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 c67ce758412e..c931463f75d9 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -102,6 +102,9 @@ 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;
 };
 
 /*
-- 
2.21.3