linux-kernel - [PATCH 4/6] KVM: SVM: fix races in the AVIC incomplete IPI delivery to vCPUs

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Date:   Thu,  9 Dec 2021 13:54:38 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND
        64-BIT)), Wanpeng Li <wanpengli@...cent.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 4/6] KVM: SVM: fix races in the AVIC incomplete IPI delivery to vCPUs

If the target vCPU has AVIC inhibited while the source vCPU isn't,
we need to set irr_pending, for the target to notice the interrupt.
Do it always to be safe, the same as in svm_deliver_avic_intr.

Also if the target has AVIC inhibited, the same kind of races
that happen in svm_deliver_avic_intr can happen here as well,
so apply the same approach of kicking the target vCPUs.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/avic.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 8c1b934bfa9b..bdfc37caa64a 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -304,8 +304,17 @@ static void avic_kick_target_vcpus(struct kvm *kvm, struct kvm_lapic *source,
 	kvm_for_each_vcpu(i, vcpu, kvm) {
 		if (kvm_apic_match_dest(vcpu, source, icrl & APIC_SHORT_MASK,
 					GET_APIC_DEST_FIELD(icrh),
-					icrl & APIC_DEST_MASK))
-			kvm_vcpu_wake_up(vcpu);
+					icrl & APIC_DEST_MASK)) {
+
+			vcpu->arch.apic->irr_pending = true;
+			kvm_make_request(KVM_REQ_EVENT, vcpu);
+			/*
+			 * The target vCPU might have AVIC inhibited,
+			 * so we have to kick it, to make sure it processes
+			 * the interrupt.
+			 */
+			kvm_vcpu_kick(vcpu);
+		}
 	}
 }
 
-- 
2.26.3