linux-kernel - [PATCH 2/2] KVM: x86: check_nested_events if there is an injectable NMI

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Date:   Tue, 14 Apr 2020 16:11:07 -0400
From:   Cathy Avery <cavery@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        pbonzini@...hat.com
Cc:     vkuznets@...hat.com, wei.huang2@....com
Subject: [PATCH 2/2] KVM: x86: check_nested_events if there is an injectable NMI

With NMI intercept moved to check_nested_events there is a race
condition where vcpu->arch.nmi_pending is set late causing
the execution of check_nested_events to not setup correctly
for nested.exit_required. A second call to check_nested_events
allows the injectable nmi to be detected in time in order to
require immediate exit from L2 to L1.

Signed-off-by: Cathy Avery <cavery@...hat.com>
---
 arch/x86/kvm/x86.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 027dfd278a97..ecfafcd93536 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7734,10 +7734,17 @@ static int inject_pending_event(struct kvm_vcpu *vcpu)
 		vcpu->arch.smi_pending = false;
 		++vcpu->arch.smi_count;
 		enter_smm(vcpu);
-	} else if (vcpu->arch.nmi_pending && kvm_x86_ops.nmi_allowed(vcpu)) {
-		--vcpu->arch.nmi_pending;
-		vcpu->arch.nmi_injected = true;
-		kvm_x86_ops.set_nmi(vcpu);
+	} else if (vcpu->arch.nmi_pending) {
+		if (is_guest_mode(vcpu) && kvm_x86_ops.check_nested_events) {
+			r = kvm_x86_ops.check_nested_events(vcpu);
+			if (r != 0)
+				return r;
+		}
+		if (kvm_x86_ops.nmi_allowed(vcpu)) {
+			--vcpu->arch.nmi_pending;
+			vcpu->arch.nmi_injected = true;
+			kvm_x86_ops.set_nmi(vcpu);
+		}
 	} else if (kvm_cpu_has_injectable_intr(vcpu)) {
 		/*
 		 * Because interrupts can be injected asynchronously, we are
-- 
2.20.1