if ((info->flags & X86_IRQ_ALLOC_CONTIGUOUS_VECTORS) && nr_irqs > 1)
return -ENOSYS;
+ /*
+ * Catch any attempt to touch the cascade interrupt on a PIC
+ * equipped system.
+ */
+ if (WARN_ON_ONCE(info->flags & X86_IRQ_ALLOC_LEGACY &&
+ virq == PIC_CASCADE_IR))
+ return -EINVAL;
+
for (i = 0; i < nr_irqs; i++) {
irqd = irq_domain_get_irq_data(domain, virq + i);
BUG_ON(!irqd);
/* Mark the preallocated legacy interrupts */
for (i = 0; i < nr_legacy_irqs(); i++) {
+ /*
+ * Don't touch the cascade interrupt. It's unusable
+ * on PIC equipped machines. See the large comment
+ * in the IO/APIC code.
+ */
if (i != PIC_CASCADE_IR)
irq_matrix_assign(vector_matrix, ISA_IRQ_VECTOR(i));
}