KVM: Drop interrupt shadow when single stepping should be done only on VMX

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: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>

arch/x86/kvm/vmx.c

@@ -3453,6 +3453,14 @@ 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
 	 */

arch/x86/kvm/x86.c

@@ -3361,9 +3361,6 @@ 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);