KVM: VMX: Provide support for user space injected NMIs

This patch adds the required bits to the VMX side for user space
injected NMIs. As with the preexisting in-kernel irqchip support, the
CPU must provide the "virtual NMI" feature for proper tracking of the
NMI blocking state.

Based on the original patch by Sheng Yang.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Sheng Yang <sheng.yang@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/vmx.c

@@ -2360,6 +2360,7 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
+	++vcpu->stat.nmi_injections;
 	if (vcpu->arch.rmode.active) {
 		vmx->rmode.irq.pending = true;
 		vmx->rmode.irq.vector = NMI_VECTOR;
@@ -2428,6 +2429,30 @@ static void do_interrupt_requests(struct kvm_vcpu *vcpu,
 {
 	vmx_update_window_states(vcpu);
 
+	if (cpu_has_virtual_nmis()) {
+		if (vcpu->arch.nmi_pending && !vcpu->arch.nmi_injected) {
+			if (vcpu->arch.nmi_window_open) {
+				vcpu->arch.nmi_pending = false;
+				vcpu->arch.nmi_injected = true;
+			} else {
+				enable_nmi_window(vcpu);
+				return;
+			}
+		}
+		if (vcpu->arch.nmi_injected) {
+			vmx_inject_nmi(vcpu);
+			if (vcpu->arch.nmi_pending
+			    || kvm_run->request_nmi_window)
+				enable_nmi_window(vcpu);
+			else if (vcpu->arch.irq_summary
+				 || kvm_run->request_interrupt_window)
+				enable_irq_window(vcpu);
+			return;
+		}
+		if (!vcpu->arch.nmi_window_open || kvm_run->request_nmi_window)
+			enable_nmi_window(vcpu);
+	}
+
 	if (vcpu->arch.interrupt_window_open) {
 		if (vcpu->arch.irq_summary && !vcpu->arch.interrupt.pending)
 			kvm_do_inject_irq(vcpu);
@@ -2959,6 +2984,14 @@ static int handle_nmi_window(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, cpu_based_vm_exec_control);
 	++vcpu->stat.nmi_window_exits;
 
+	/*
+	 * If the user space waits to inject a NMI, exit as soon as possible
+	 */
+	if (kvm_run->request_nmi_window && !vcpu->arch.nmi_pending) {
+		kvm_run->exit_reason = KVM_EXIT_NMI_WINDOW_OPEN;
+		return 0;
+	}
+
 	return 1;
 }