This represents the following 3 patches (attached to bug 730765), but applied
to the hardy kernel:
  http://lkml.org/lkml/2010/9/18/288
  http://lkml.org/lkml/2010/9/18/282
  http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=3588fe2e3f36543664beafedd3bb6dc3ffa896c5

Note that the third patch stacks over the change made in the first.

diff --git a/arch/x86/xen/events.c b/arch/x86/xen/events.c
index 6d1da58..c8a19f0 100644
--- a/arch/x86/xen/events.c
+++ b/arch/x86/xen/events.c
@@ -258,7 +258,7 @@ int bind_evtchn_to_irq(unsigned int evtchn)
 
 		dynamic_irq_init(irq);
 		set_irq_chip_and_handler_name(irq, &xen_dynamic_chip,
-					      handle_level_irq, "event");
+					      handle_fasteoi_irq, "event");
 
 		evtchn_to_irq[evtchn] = irq;
 		irq_info[irq] = mk_irq_info(IRQT_EVTCHN, 0, evtchn);
@@ -286,8 +286,8 @@ static int bind_ipi_to_irq(unsigned int ipi, unsigned int cpu)
 			goto out;
 
 		dynamic_irq_init(irq);
-		set_irq_chip_and_handler_name(irq, &xen_dynamic_chip,
-					      handle_level_irq, "ipi");
+		set_irq_chip_and_handler_name(irq, &xen_percpu_chip,
+					      handle_percpu_irq, "ipi");
 
 		bind_ipi.vcpu = cpu;
 		if (HYPERVISOR_event_channel_op(EVTCHNOP_bind_ipi,
@@ -331,8 +331,8 @@ static int bind_virq_to_irq(unsigned int virq, unsigned int cpu)
 		irq = find_unbound_irq();
 
 		dynamic_irq_init(irq);
-		set_irq_chip_and_handler_name(irq, &xen_dynamic_chip,
-					      handle_level_irq, "virq");
+		set_irq_chip_and_handler_name(irq, &xen_percpu_chip,
+					      handle_percpu_irq, "virq");
 
 		evtchn_to_irq[evtchn] = irq;
 		irq_info[irq] = mk_irq_info(IRQT_VIRQ, virq, evtchn);
@@ -486,6 +486,9 @@ fastcall void xen_evtchn_do_upcall(struct pt_regs *regs)
 			int port = (word_idx * BITS_PER_LONG) + bit_idx;
 			int irq = evtchn_to_irq[port];
 
+			mask_evtchn(port);
+			clear_evtchn(port);
+
 			if (irq != -1) {
 				regs->orig_eax = ~irq;
 				do_IRQ(regs);
@@ -545,10 +548,10 @@ static void ack_dynirq(unsigned int irq)
 {
 	int evtchn = evtchn_from_irq(irq);
 
-	move_native_irq(irq);
+	move_masked_irq(irq);
 
 	if (VALID_EVTCHN(evtchn))
-		clear_evtchn(evtchn);
+		unmask_evtchn(evtchn);
 }
 
 static int retrigger_dynirq(unsigned int irq)
@@ -568,11 +571,22 @@ static struct irq_chip xen_dynamic_chip __read_mostly = {
 	.name		= "xen-dyn",
 	.mask		= disable_dynirq,
 	.unmask		= enable_dynirq,
-	.ack		= ack_dynirq,
+	.eoi		= ack_dynirq,
 	.set_affinity	= set_affinity_irq,
 	.retrigger	= retrigger_dynirq,
 };
 
+static struct irq_chip xen_percpu_chip __read_mostly = {
+	.name    = "xen-percpu",
+
+	.disable = disable_dynirq,
+	.mask    = disable_dynirq,
+	.unmask     = enable_dynirq,
+
+	.ack     = ack_dynirq,
+};
+
+
 void __init xen_init_IRQ(void)
 {
 	int i;