diff -r 4b51d081378d xen/arch/ia64/linux-xen/iosapic.c
--- a/xen/arch/ia64/linux-xen/iosapic.c	Wed Jun 28 07:52:21 2006 -0600
+++ b/xen/arch/ia64/linux-xen/iosapic.c	Fri Jun 30 12:47:17 2006 -0600
@@ -1122,6 +1122,53 @@ core_initcall (iosapic_enable_kmalloc);
 #endif
 
 #ifdef XEN
+static void unmask_xen_redirect(unsigned int irq)
+{
+	int i;
+
+	for (i = 0 ; i < NR_IRQS ; i++) {
+		if (guest_vector[i].vector == irq) {
+			guest_vector[i].enabled = 1;
+			return;
+		}
+	}
+}
+
+static void mask_xen_redirect(unsigned int irq)
+{
+	int i;
+
+	for (i = 0 ; i < NR_IRQS ; i++) {
+		if (guest_vector[i].vector == irq) {
+			guest_vector[i].enabled = 0;
+			return;
+		}
+	}
+}
+
+static unsigned int startup_xen_redirect(unsigned int irq)
+{
+	unmask_xen_redirect(irq);
+	return 0;
+}
+
+#define shutdown_xen_redirect	mask_xen_redirect
+#define enable_xen_redirect	unmask_xen_redirect
+#define disable_xen_redirect	mask_xen_redirect
+#define ack_xen_redirect	nop
+#define end_xen_redirect	nop
+
+struct hw_interrupt_type irq_type_xen_redirect = {
+	.typename =	"XEN-redirect",
+	.startup =	startup_xen_redirect,
+	.shutdown =	shutdown_xen_redirect,
+	.enable =	enable_xen_redirect,
+	.disable =	disable_xen_redirect,
+	.ack =		ack_xen_redirect,
+	.end =		end_xen_redirect,
+	.set_affinity =	NULL,
+};
+
 /* nop for now */
 void set_irq_affinity_info(unsigned int irq, int hwid, int redir) {}
 
@@ -1161,6 +1208,7 @@ int iosapic_guest_write(unsigned long ph
 	struct iosapic_intr_info *info;
 	struct rte_entry rte;
 	unsigned long flags;
+	int xen_vector;
 
 	if ((id = (iosapic_physbase_to_id(physbase))) < 0)
 	    return -EINVAL;
@@ -1185,13 +1233,41 @@ int iosapic_guest_write(unsigned long ph
 
 	/* Sanity check. Vector should be allocated before this update */
 	if ((rte_index > ios->num_rte) ||
-	    test_bit(vec, ia64_xen_vector) ||
 	    ((vec > IA64_FIRST_DEVICE_VECTOR) &&
 	     (vec < IA64_LAST_DEVICE_VECTOR) &&
 	     (!test_bit(vec - IA64_FIRST_DEVICE_VECTOR, ia64_vector_mask))))
 	    return -EINVAL;
 
 	gsi = ios->gsi_base + rte_index;
+	xen_vector = gsi_to_vector(gsi);
+	if (xen_vector >= 0 && test_bit(xen_vector, ia64_xen_vector)) {
+
+		if (guest_vector[xen_vector].vector) {
+			printk("WARN: Xen GSI %d (vector %d) already in use "
+			       "and redirected to guest vector %d\n", gsi,
+			       xen_vector, guest_vector[xen_vector].vector);
+			return -EINVAL;
+		}
+
+		info = &iosapic_intr_info[xen_vector];
+	    	if ((info->trigger != rte.lo.trigger) ||
+		    (info->polarity != rte.lo.polarity)) {
+			printk("WARN: Xen GSI %d (vector %d) trigger/polairty "
+			       "incompatible with guest vector %d\n", gsi,
+			       xen_vector, vec);
+			return -EINVAL;
+		}
+
+		spin_lock_irqsave(&irq_descp(vec)->lock, flags);
+		irq_descp(vec)->handler = &irq_type_xen_redirect;
+		spin_unlock_irqrestore(&irq_descp(vec)->lock, flags);
+
+		spin_lock_irqsave(&irq_descp(xen_vector)->lock, flags);
+		guest_vector[xen_vector].vector = vec;
+		spin_unlock_irqrestore(&irq_descp(xen_vector)->lock, flags);
+		return 0;
+	}
+
 	info = &iosapic_intr_info[vec];
 	spin_lock_irqsave(&irq_descp(vec)->lock, flags);
 	spin_lock(&iosapic_lock);
diff -r 4b51d081378d xen/arch/ia64/xen/irq.c
--- a/xen/arch/ia64/xen/irq.c	Wed Jun 28 07:52:21 2006 -0600
+++ b/xen/arch/ia64/xen/irq.c	Fri Jun 30 12:47:17 2006 -0600
@@ -45,6 +45,7 @@
 #include <asm/delay.h>
 #include <xen/irq.h>
 #include <asm/hw_irq.h>
+#include <asm/iosapic.h>
 
 #include <xen/event.h>
 #define apicid_to_phys_cpu_present(x)	1
@@ -75,6 +76,8 @@ irq_desc_t irq_desc[NR_IRQS] __cacheline
 		.lock = SPIN_LOCK_UNLOCKED
 	}
 };
+
+struct guest_vector_t guest_vector[NR_IRQS];
 
 void __do_IRQ_guest(int irq);
 
@@ -211,6 +214,16 @@ fastcall unsigned int __do_IRQ(unsigned 
 	desc->status &= ~IRQ_INPROGRESS;
 
 out:
+	if (guest_vector[irq].enabled) {
+		irq_desc_t *guest_desc = irq_desc + guest_vector[irq].vector;
+
+		if (likely(guest_desc->status & IRQ_GUEST)) {
+			spin_lock(&guest_desc->lock);
+			__do_IRQ_guest(guest_vector[irq].vector);
+			spin_unlock(&guest_desc->lock);
+		}
+	}
+
 	/*
 	 * The ->end() handler has to deal with interrupts which got
 	 * disabled while the handler was running.
diff -r 4b51d081378d xen/include/asm-ia64/linux-xen/asm/iosapic.h
--- a/xen/include/asm-ia64/linux-xen/asm/iosapic.h	Wed Jun 28 07:52:21 2006 -0600
+++ b/xen/include/asm-ia64/linux-xen/asm/iosapic.h	Fri Jun 30 12:47:17 2006 -0600
@@ -159,6 +159,13 @@ struct rte_entry {
 #define IOSAPIC_RTEINDEX(reg)	(((reg) - 0x10) >> 1)
 extern unsigned long ia64_vector_mask[];
 extern unsigned long ia64_xen_vector[];
+
+struct guest_vector_t {
+	u16	vector		: 8,
+		__reserved	: 7,
+		enabled		: 1;
+};
+extern struct guest_vector_t guest_vector[];
 #endif /* XEN */
 
 # endif /* !__ASSEMBLY__ */