KVM: nVMX: Ack and write vector info to intr_info if L1 asks us to

This feature emulates the "Acknowledge interrupt on exit" behavior.
We can safely emulate it for L1 to run L2 even if L0 itself has it
disabled (to run L1).

Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/vmx.c

@@ -4526,6 +4526,16 @@ static bool nested_exit_on_intr(struct kvm_vcpu *vcpu)
 		PIN_BASED_EXT_INTR_MASK;
 }
 
+/*
+ * In nested virtualization, check if L1 has set
+ * VM_EXIT_ACK_INTR_ON_EXIT
+ */
+static bool nested_exit_intr_ack_set(struct kvm_vcpu *vcpu)
+{
+	return get_vmcs12(vcpu)->vm_exit_controls &
+		VM_EXIT_ACK_INTR_ON_EXIT;
+}
+
 static bool nested_exit_on_nmi(struct kvm_vcpu *vcpu)
 {
 	return get_vmcs12(vcpu)->pin_based_vm_exec_control &
@@ -8563,6 +8573,14 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
 	prepare_vmcs12(vcpu, vmcs12, exit_reason, exit_intr_info,
 		       exit_qualification);
 
+	if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
+	    && nested_exit_intr_ack_set(vcpu)) {
+		int irq = kvm_cpu_get_interrupt(vcpu);
+		WARN_ON(irq < 0);
+		vmcs12->vm_exit_intr_info = irq |
+			INTR_INFO_VALID_MASK | INTR_TYPE_EXT_INTR;
+	}
+
 	trace_kvm_nested_vmexit_inject(vmcs12->vm_exit_reason,
 				       vmcs12->exit_qualification,
 				       vmcs12->idt_vectoring_info_field,