[PATCH MANUALSEL 5.15 1/2] KVM: x86: lapic: don't touch irr_pending in kvm_apic_update_apicv when inhibiting it

[Sasha Levin <sashal@kernel.org>]

From: Maxim Levitsky <mlevitsk@redhat.com>

[ Upstream commit 755c2bf878607dbddb1423df9abf16b82205896f ]

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

Also logic in avic_kick_target_vcpu doesn't expect a race with this
function so 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@redhat.com>
Message-Id: <20220207155447.840194-9-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/lapic.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 91c2dc9f198df..5f935e7a09566 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2306,7 +2306,12 @@ 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 clear irr_pending, searching the IRR can race with
+		 * updates from the CPU as APICv is still active from hardware's
+		 * perspective.  The flag will be cleared as appropriate when
+		 * KVM injects the interrupt.
+		 */
 		apic->isr_count = count_vectors(apic->regs + APIC_ISR);
 	}
 }
-- 
2.34.1