[08/30] KVM: x86: lapic: don't touch irr_pending in kvm_apic_update_apicv when inhibiting it

Commit Message

Maxim Levitsky Feb. 7, 2022, 3:28 p.m. UTC

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 <[e-mail]>
---
 arch/x86/kvm/lapic.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Patch

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0da7d0960fcb5..dd4e2888c244b 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2307,7 +2307,12 @@  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);
 	}
 }