linux-kernel - [PATCH] KVM: x86: Exit to userspace when kvm_check_nested

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Date:   Wed, 28 Jul 2021 07:53:17 -0400
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>
Subject: [PATCH] KVM: x86: Exit to userspace when kvm_check_nested_events fails

From: Jim Mattson <jmattson@...gle.com>

If kvm_check_nested_events fails due to raising an
EXIT_REASON_INTERNAL_ERROR, propagate it to userspace
immediately, even if the vCPU would otherwise be sleeping.
This happens for example when the posted interrupt descriptor
points outside guest memory.

Reported-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/x86.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 348452bb16bc..916c976e99ab 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9752,10 +9752,14 @@ static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
 	return 1;
 }
 
-static inline bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
+static inline int kvm_vcpu_running(struct kvm_vcpu *vcpu)
 {
-	if (is_guest_mode(vcpu))
-		kvm_check_nested_events(vcpu);
+	int r;
+	if (is_guest_mode(vcpu)) {
+		r = kvm_check_nested_events(vcpu);
+		if (r < 0 && r != -EBUSY)
+			return r;
+	}
 
 	return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
 		!vcpu->arch.apf.halted);
@@ -9770,12 +9774,16 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
 	vcpu->arch.l1tf_flush_l1d = true;
 
 	for (;;) {
-		if (kvm_vcpu_running(vcpu)) {
-			r = vcpu_enter_guest(vcpu);
-		} else {
-			r = vcpu_block(kvm, vcpu);
+		r = kvm_vcpu_running(vcpu);
+		if (r < 0) {
+			r = 0;
+			break;
 		}
 
+		if (r)
+			r = vcpu_enter_guest(vcpu);
+		else
+			r = vcpu_block(kvm, vcpu);
 		if (r <= 0)
 			break;
 
-- 
2.27.0