xen/events: switch user event channels to lateeoi model

Instead of disabling the irq when an event is received and enabling
it again when handled by the user process use the lateeoi model.

This is part of XSA-332.

Cc: stable@vger.kernel.org
Reported-by: Julien Grall <julien@xen.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Wei Liu <wl@xen.org>

drivers/xen/evtchn.c

@@ -167,7 +167,6 @@ static irqreturn_t evtchn_interrupt(int irq, void *data)
 	     "Interrupt for port %u, but apparently not enabled; per-user %p\n",
 	     evtchn->port, u);
 
-	disable_irq_nosync(irq);
 	evtchn->enabled = false;
 
 	spin_lock(&u->ring_prod_lock);
@@ -293,7 +292,7 @@ static ssize_t evtchn_write(struct file *file, const char __user *buf,
 		evtchn = find_evtchn(u, port);
 		if (evtchn && !evtchn->enabled) {
 			evtchn->enabled = true;
-			enable_irq(irq_from_evtchn(port));
+			xen_irq_lateeoi(irq_from_evtchn(port), 0);
 		}
 	}
 
@@ -393,7 +392,7 @@ static int evtchn_bind_to_user(struct per_user_data *u, evtchn_port_t port)
 	if (rc < 0)
 		goto err;
 
-	rc = bind_evtchn_to_irqhandler(port, evtchn_interrupt, 0,
+	rc = bind_evtchn_to_irqhandler_lateeoi(port, evtchn_interrupt, 0,
 					       u->name, evtchn);
 	if (rc < 0)
 		goto err;