linux-kernel - [PATCH v2 4/5] KVM: x86: don't touch irr_pending in kvm_apic_update

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Message-Id: <20211213104634.199141-5-mlevitsk@redhat.com>
Date:   Mon, 13 Dec 2021 12:46:33 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joerg Roedel <joro@...tes.org>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v2 4/5] KVM: x86: don't touch irr_pending in kvm_apic_update_apicv when inhibiting it

kvm_apic_update_apicv is called when AVIC is still active, thus IRR bits
can be set by the CPU after it was called, and won't cause the irr_pending
to be set to true.

Also the logic in avic_kick_target_vcpu doesn't expect a race with this
function.

To make it simple, just keep irr_pending set to true and
let the next interrupt injection to the guest clear it.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/lapic.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index baca9fa37a91c..6e1fbbf4c508b 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2312,7 +2312,10 @@ void kvm_apic_update_apicv(struct kvm_vcpu *vcpu)
 		apic->irr_pending = true;
 		apic->isr_count = 1;
 	} else {
-		apic->irr_pending = (apic_search_irr(apic) != -1);
+		/*
+		 * Don't touch irr_pending, let it be cleared when
+		 * we process the interrupt
+		 */
 		apic->isr_count = count_vectors(apic->regs + APIC_ISR);
 	}
 }
-- 
2.26.3