xen/events: bind all new interdomain events to VCPU0

Commit fc087e10734a4d3e40693fc099461ec1270b3fff (xen/events: remove
unnecessary init_evtchn_cpu_bindings()) causes a regression.

The kernel-side VCPU binding was not being correctly set for newly
allocated or bound interdomain events.  In ARM guests where 2-level
events were used, this would result in no interdomain events being
handled because the kernel-side VCPU masks would all be clear.

x86 guests would work because the irq affinity was set during irq
setup and this would set the correct kernel-side VCPU binding.

Fix this by properly initializing the kernel-side VCPU binding in
bind_evtchn_to_irq().

Reported-and-tested-by: Julien Grall <julien.grall@linaro.org>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/events/events_base.c

@@ -862,6 +862,8 @@ int bind_evtchn_to_irq(unsigned int evtchn)
 			irq = ret;
 			goto out;
 		}
+		/* New interdomain events are bound to VCPU 0. */
+		bind_evtchn_to_cpu(evtchn, 0);
 	} else {
 		struct irq_info *info = info_for_irq(irq);
 		WARN_ON(info == NULL || info->type != IRQT_EVTCHN);