genirq: Let irq_set_vcpu_affinity() iterate over hierarchy

When assigning an interrupt to a vcpu, it is not unlikely that
the level of the hierarchy implementing irq_set_vcpu_affinity
is not the top level (think a generic MSI domain on top of a
virtualization aware interrupt controller).

In such a case, let's iterate over the hierarchy until we find
an irqchip implementing it.
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>

kernel/irq/manage.c

@@ -400,8 +400,18 @@ int irq_set_vcpu_affinity(unsigned int irq, void *vcpu_info)
 		return -EINVAL;
 
 	data = irq_desc_get_irq_data(desc);
-	chip = irq_data_get_irq_chip(data);
-	if (chip && chip->irq_set_vcpu_affinity)
+	do {
+		chip = irq_data_get_irq_chip(data);
+		if (chip && chip->irq_set_vcpu_affinity)
+			break;
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+		data = data->parent_data;
+#else
+		data = NULL;
+#endif
+	} while (data);
+
+	if (data)
 		ret = chip->irq_set_vcpu_affinity(data, vcpu_info);
 	irq_put_desc_unlock(desc, flags);