[PATCH] Drop interrupt shadow when single stepping should be done only on VMX.

[Gleb Natapov <gleb@redhat.com>]

The problem exists only on VMX. Also currently we skip this step if
there is pending exception. The patch fixes this too.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
---
 arch/x86/kvm/vmx.c |    8 ++++++++
 arch/x86/kvm/x86.c |    3 ---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index fe2ce2b..ec378c1 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3388,6 +3388,14 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	if (test_bit(VCPU_REGS_RIP, (unsigned long *)&vcpu->arch.regs_dirty))
 		vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
 
+	/* When single-stepping over STI and MOV SS, we must clear the
+	 * corresponding interruptibility bits in the guest state. Otherwise
+	 * vmentry fails as it then expects bit 14 (BS) in pending debug
+	 * exceptions being set, but that's not correct for the guest debugging
+	 * case. */
+	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
+		vmx_set_interrupt_shadow(vcpu, 0);
+
 	/*
 	 * Loading guest fpu may have cleared host cr0.ts
 	 */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a08d96f..82585ae 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3153,9 +3153,6 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu)
 
 static void inject_pending_irq(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
-	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
-		kvm_x86_ops->set_interrupt_shadow(vcpu, 0);
-
 	/* try to reinject previous events if any */
 	if (vcpu->arch.nmi_injected) {
 		kvm_x86_ops->set_nmi(vcpu);
-- 
1.6.2.1