KVM: arm64: vgic: Be tolerant to the lack of maintenance interrupt masking

As it turns out, not all the interrupt controllers are able to
expose a vGIC maintenance interrupt that can be independently
enabled/disabled.

And to be fair, it doesn't really matter as all we require is
for the interrupt to kick us out of guest mode out way or another.

To that effect, add gic_kvm_info.no_maint_irq_mask for an interrupt
controller to advertise the lack of masking.
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/vgic/vgic-init.c

@@ -519,12 +519,15 @@ void kvm_vgic_init_cpu_hardware(void)
  */
 int kvm_vgic_hyp_init(void)
 {
+	bool has_mask;
 	int ret;
 
 	if (!gic_kvm_info)
 		return -ENODEV;
 
-	if (!gic_kvm_info->maint_irq) {
+	has_mask = !gic_kvm_info->no_maint_irq_mask;
+
+	if (has_mask && !gic_kvm_info->maint_irq) {
 		kvm_err("No vgic maintenance irq\n");
 		return -ENXIO;
 	}
@@ -552,6 +555,9 @@ int kvm_vgic_hyp_init(void)
 	if (ret)
 		return ret;
 
+	if (!has_mask)
+		return 0;
+
 	ret = request_percpu_irq(kvm_vgic_global_state.maint_irq,
 				 vgic_maintenance_handler,
 				 "vgic", kvm_get_running_vcpus());

include/linux/irqchip/arm-vgic-info.h

@@ -24,6 +24,8 @@ struct gic_kvm_info {
 	struct resource vcpu;
 	/* Interrupt number */
 	unsigned int	maint_irq;
+	/* No interrupt mask, no need to use the above field */
+	bool		no_maint_irq_mask;
 	/* Virtual control interface */
 	struct resource vctrl;
 	/* vlpi support */