From: Ladi Prosek <lprosek@redhat.com>
Date: Wed, 21 Jun 2017 09:07:00 +0200
Subject: KVM: SVM: don't NMI singlestep over event injection
Git-commit: a12713c25b36cbbc1a3204b2a49a72f7bc8a8847
Patch-mainline: v4.13-rc1
References: fate#323405

Singlestepping is enabled by setting the TF flag and care must be
taken to not let the guest see (and reuse at an inconvenient time)
the modified rflag value. One such case is event injection, as part
of which flags are pushed on the stack and restored later on iret.

This commit disables singlestepping when we're about to inject an
event and forces an immediate exit for us to re-evaluate the NMI
related state.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/kvm/svm.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4844,6 +4844,22 @@ static void svm_vcpu_run(struct kvm_vcpu
 	if (unlikely(svm->nested.exit_required))
 		return;
 
+	/*
+	 * Disable singlestep if we're injecting an interrupt/exception.
+	 * We don't want our modified rflags to be pushed on the stack where
+	 * we might not be able to easily reset them if we disabled NMI
+	 * singlestep later.
+	 */
+	if (svm->nmi_singlestep && svm->vmcb->control.event_inj) {
+		/*
+		 * Event injection happens before external interrupts cause a
+		 * vmexit and interrupts are disabled here, so smp_send_reschedule
+		 * is enough to force an immediate vmexit.
+		 */
+		disable_nmi_singlestep(svm);
+		smp_send_reschedule(vcpu->cpu);
+	}
+
 	pre_svm_run(svm);
 
 	sync_lapic_to_cr8(vcpu);