KVM: nVMX: Report NMIs as allowed when in L2 and Exit-on-NMI is set

Report NMIs as allowed when the vCPU is in L2 and L2 is being run with
Exit-on-NMI enabled, as NMIs are always unblocked from L1's perspective
in this case.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200423022550.15113-7-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -698,11 +698,6 @@ static bool nested_exit_intr_ack_set(struct kvm_vcpu *vcpu)
 		VM_EXIT_ACK_INTR_ON_EXIT;
 }
 
-static bool nested_exit_on_nmi(struct kvm_vcpu *vcpu)
-{
-	return nested_cpu_has_nmi_exiting(get_vmcs12(vcpu));
-}
-
 static int nested_vmx_check_apic_access_controls(struct kvm_vcpu *vcpu,
 					  struct vmcs12 *vmcs12)
 {

arch/x86/kvm/vmx/nested.h

@@ -225,6 +225,11 @@ static inline bool nested_cpu_has_save_preemption_timer(struct vmcs12 *vmcs12)
 	    VM_EXIT_SAVE_VMX_PREEMPTION_TIMER;
 }
 
+static inline bool nested_exit_on_nmi(struct kvm_vcpu *vcpu)
+{
+	return nested_cpu_has_nmi_exiting(get_vmcs12(vcpu));
+}
+
 /*
  * In nested virtualization, check if L1 asked to exit on external interrupts.
  * For most existing hypervisors, this will always return true.

arch/x86/kvm/vmx/vmx.c

@@ -4515,6 +4515,9 @@ static bool vmx_nmi_allowed(struct kvm_vcpu *vcpu)
 	if (to_vmx(vcpu)->nested.nested_run_pending)
 		return false;
 
+	if (is_guest_mode(vcpu) && nested_exit_on_nmi(vcpu))
+		return true;
+
 	if (!enable_vnmi &&
 	    to_vmx(vcpu)->loaded_vmcs->soft_vnmi_blocked)
 		return false;