linux-kernel - [PATCH v4 13/16] KVM: SVM: avoid refreshing avic if its state didn't change

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Date:   Tue, 10 Aug 2021 23:52:48 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v4 13/16] KVM: SVM: avoid refreshing avic if its state didn't change

Since AVIC can be inhibited and uninhibited rapidly it is possible that
we have nothing to do by the time the svm_refresh_apicv_exec_ctrl
is called.

Detect and avoid this, which will be useful when we will start calling
avic_vcpu_load/avic_vcpu_put when the avic inhibition state changes.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/x86.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b6185921fe44..e2ec45e3dc0a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9239,12 +9239,18 @@ void kvm_make_scan_ioapic_request(struct kvm *kvm)
 
 void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
 {
+	bool activate;
+
 	if (!lapic_in_kernel(vcpu))
 		return;
 
 	mutex_lock(&vcpu->kvm->arch.apicv_update_lock);
 
-	vcpu->arch.apicv_active = kvm_apicv_activated(vcpu->kvm);
+	activate = kvm_apicv_activated(vcpu->kvm);
+	if (vcpu->arch.apicv_active == activate)
+		goto out;
+
+	vcpu->arch.apicv_active = activate;
 	kvm_apic_update_apicv(vcpu);
 	static_call(kvm_x86_refresh_apicv_exec_ctrl)(vcpu);
 
@@ -9257,6 +9263,7 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
 	if (!vcpu->arch.apicv_active)
 		kvm_make_request(KVM_REQ_EVENT, vcpu);
 
+out:
 	mutex_unlock(&vcpu->kvm->arch.apicv_update_lock);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_update_apicv);
-- 
2.26.3