xen64: add identity irq->vector map

The x86_64 interrupt subsystem is oriented towards vectors, as opposed
to a flat irq space as it is in x86-32.  This patch adds a simple
identity irq->vector mapping so that we can continue to feed irqs into
do_IRQ() and get a good result.

Ideally x86_32 will unify with the 64-bit code and use vectors too.
At that point we can move to mapping event channels to vectors, which
will allow us to economise on irqs (so per-cpu event channels can
share irqs, rather than having to allocte one per cpu, for example).

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stephen Tweedie <sct@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/xen/enlighten.c

@@ -1085,8 +1085,25 @@ static const struct pv_cpu_ops xen_cpu_ops __initdata = {
 	},
 };
 
+static void __init __xen_init_IRQ(void)
+{
+#ifdef CONFIG_X86_64
+	int i;
+
+	/* Create identity vector->irq map */
+	for(i = 0; i < NR_VECTORS; i++) {
+		int cpu;
+
+		for_each_possible_cpu(cpu)
+			per_cpu(vector_irq, cpu)[i] = i;
+	}
+#endif	/* CONFIG_X86_64 */
+
+	xen_init_IRQ();
+}
+
 static const struct pv_irq_ops xen_irq_ops __initdata = {
-	.init_IRQ = xen_init_IRQ,
+	.init_IRQ = __xen_init_IRQ,
 	.save_fl = xen_save_fl,
 	.restore_fl = xen_restore_fl,
 	.irq_disable = xen_irq_disable,