KVM: VMX: Support for NMI task gates

Properly set GUEST_INTR_STATE_NMI and reset nmi_injected when a
task-switch vmexit happened due to a task gate being used for handling
NMIs. Also avoid the false warning about valid vectoring info in
kvm_handle_exit.

Based on original patch by Gleb Natapov.
Signed-off-by: NGleb Natapov <gleb@redhat.com>
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>

arch/x86/kvm/vmx.c

@@ -2832,6 +2832,7 @@ static int handle_apic_access(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 
 static int handle_task_switch(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	unsigned long exit_qualification;
 	u16 tss_selector;
 	int reason;
@@ -2839,6 +2840,15 @@ static int handle_task_switch(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
 
 	reason = (u32)exit_qualification >> 30;
+	if (reason == TASK_SWITCH_GATE && vmx->vcpu.arch.nmi_injected &&
+	    (vmx->idt_vectoring_info & VECTORING_INFO_VALID_MASK) &&
+	    (vmx->idt_vectoring_info & VECTORING_INFO_TYPE_MASK)
+	    == INTR_TYPE_NMI_INTR) {
+		vcpu->arch.nmi_injected = false;
+		if (cpu_has_virtual_nmis())
+			vmcs_set_bits(GUEST_INTERRUPTIBILITY_INFO,
+				      GUEST_INTR_STATE_NMI);
+	}
 	tss_selector = exit_qualification;
 
 	return kvm_task_switch(vcpu, tss_selector, reason);
@@ -3012,9 +3022,11 @@ static int kvm_handle_exit(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 
 	if ((vectoring_info & VECTORING_INFO_VALID_MASK) &&
 			(exit_reason != EXIT_REASON_EXCEPTION_NMI &&
-			exit_reason != EXIT_REASON_EPT_VIOLATION))
-		printk(KERN_WARNING "%s: unexpected, valid vectoring info and "
-		       "exit reason is 0x%x\n", __func__, exit_reason);
+			exit_reason != EXIT_REASON_EPT_VIOLATION &&
+			exit_reason != EXIT_REASON_TASK_SWITCH))
+		printk(KERN_WARNING "%s: unexpected, valid vectoring info "
+		       "(0x%x) and exit reason is 0x%x\n",
+		       __func__, vectoring_info, exit_reason);
 	if (exit_reason < kvm_vmx_max_exit_handlers
 	    && kvm_vmx_exit_handlers[exit_reason])
 		return kvm_vmx_exit_handlers[exit_reason](vcpu, kvm_run);