linux-kernel - [PATCH] svm/avic: Do not send AVIC doorbell to self

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Message-ID: <1556890721-9613-1-git-send-email-suravee.suthikulpanit@amd.com>
Date:   Fri, 3 May 2019 13:38:53 +0000
From:   "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>
Subject: [PATCH] svm/avic: Do not send AVIC doorbell to self

AVIC doorbell is used to notify a running vCPU that interrupts
has been injected into the vCPU AVIC backing page. Current logic
checks only if a VCPU is running before sending a doorbell.
However, the doorbell is not necessary if the destination
CPU is itself.

Add logic to check currently running CPU before sending doorbell.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 arch/x86/kvm/svm.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 122788f..4bbf6fc 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5283,10 +5283,13 @@ static void svm_deliver_avic_intr(struct kvm_vcpu *vcpu, int vec)
 	kvm_lapic_set_irr(vec, vcpu->arch.apic);
 	smp_mb__after_atomic();
 
-	if (avic_vcpu_is_running(vcpu))
-		wrmsrl(SVM_AVIC_DOORBELL,
-		       kvm_cpu_get_apicid(vcpu->cpu));
-	else
+	if (avic_vcpu_is_running(vcpu)) {
+		int cpuid = vcpu->cpu;
+
+		if (cpuid != get_cpu())
+			wrmsrl(SVM_AVIC_DOORBELL, kvm_cpu_get_apicid(cpuid));
+		put_cpu();
+	} else
 		kvm_vcpu_wake_up(vcpu);
 }
 
-- 
1.8.3.1