Index: sys/xen/xen_intr.c
===================================================================
--- sys/xen/xen_intr.c
+++ sys/xen/xen_intr.c
@@ -121,10 +121,6 @@
 
 DPCPU_DECLARE(struct vcpu_info *, vcpu_info);
 
-#define	XEN_INVALID_EVTCHN	0 /* Invalid event channel */
-
-#define	is_valid_evtchn(x)	((x) != XEN_INVALID_EVTCHN)
-
 struct xenisrc {
 	xen_arch_isrc_t	xi_arch;	/* @TOP -> *xi_arch=*xenisrc */
 	enum evtchn_type xi_type;
@@ -226,7 +222,7 @@
  *        event channel globally, use evtchn_mask().
  */
 static inline void
-evtchn_cpu_mask_port(u_int cpu, evtchn_port_t port)
+xen_intr_cpu_mask_port(u_int cpu, evtchn_port_t port)
 {
 	struct xen_intr_pcpu_data *pcpu;
 
@@ -248,7 +244,7 @@
  *        also be globally enabled.  See evtchn_unmask().
  */
 static inline void
-evtchn_cpu_unmask_port(u_int cpu, evtchn_port_t port)
+xen_intr_cpu_unmask_port(u_int cpu, evtchn_port_t port)
 {
 	struct xen_intr_pcpu_data *pcpu;
 
@@ -331,7 +327,7 @@
 		return (isrc);
 	}
 
-	if (xen_intr_auto_vector_count > NR_EVENT_CHANNELS) {
+	if (xen_intr_auto_vector_count >= NR_EVENT_CHANNELS) {
 		if (!warned) {
 			warned = 1;
 			printf("%s: Event channels exhausted.\n", __func__);
@@ -374,10 +370,10 @@
 	evtchn_clear_port(isrc->xi_port);
 
 	/* Rebind port to CPU 0. */
-	evtchn_cpu_mask_port(isrc->xi_cpu, isrc->xi_port);
-	evtchn_cpu_unmask_port(0, isrc->xi_port);
+	xen_intr_cpu_mask_port(isrc->xi_cpu, isrc->xi_port);
+	xen_intr_cpu_unmask_port(0, isrc->xi_port);
 
-	if (isrc->xi_close != 0 && is_valid_evtchn(isrc->xi_port)) {
+	if (isrc->xi_close != 0) {
 		struct evtchn_close close = { .port = isrc->xi_port };
 		if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close))
 			panic("EVTCHNOP_close failed");
@@ -388,7 +384,7 @@
 	mtx_unlock(&xen_intr_isrc_lock);
 
 	isrc->xi_cpu = 0;
-	isrc->xi_port = 0;
+	isrc->xi_port = ~0;
 	isrc->xi_cookie = NULL;
 	mtx_lock(&xen_intr_x86_lock);
 	isrc->xi_type = EVTCHN_TYPE_UNBOUND;
@@ -438,7 +434,7 @@
 		return (ENOSPC);
 	mtx_lock(&xen_intr_isrc_lock);
 	isrc->xi_port = local_port;
-	xen_intr_port_to_isrc[local_port] = isrc;
+	xen_intr_port_to_isrc[isrc->xi_port] = isrc;
 	refcount_init(&isrc->xi_refcount, 1);
 	mtx_unlock(&xen_intr_isrc_lock);
 
@@ -738,7 +734,7 @@
 	int cpu = isrc->xi_cpu;
 	int error;
 
-	isrc->xi_port = 0;
+	isrc->xi_port = ~0;
 	switch (isrc->xi_type) {
 	case EVTCHN_TYPE_IPI:
 		xen_rebind_ipi(isrc);
@@ -917,7 +913,7 @@
 
 	mtx_lock(&xen_intr_isrc_lock);
 	isrc = (struct xenisrc *)base_isrc;
-	if (!is_valid_evtchn(isrc->xi_port)) {
+	if (isrc->xi_port >= NR_EVENT_CHANNELS) {
 		mtx_unlock(&xen_intr_isrc_lock);
 		return (EINVAL);
 	}
@@ -934,9 +930,9 @@
 		 * the Hypervisor at evtchn_bind_virq time, so
 		 * all we need to do is update the per-CPU masks.
 		 */
-		evtchn_cpu_mask_port(isrc->xi_cpu, isrc->xi_port);
+		xen_intr_cpu_mask_port(isrc->xi_cpu, isrc->xi_port);
 		isrc->xi_cpu = to_cpu;
-		evtchn_cpu_unmask_port(isrc->xi_cpu, isrc->xi_port);
+		xen_intr_cpu_unmask_port(isrc->xi_cpu, isrc->xi_port);
 		goto out;
 	}
 
@@ -947,9 +943,9 @@
 	if (isrc->xi_cpu != to_cpu) {
 		if (error == 0) {
 			/* Commit to new binding by removing the old one. */
-			evtchn_cpu_mask_port(isrc->xi_cpu, isrc->xi_port);
+			xen_intr_cpu_mask_port(isrc->xi_cpu, isrc->xi_port);
 			isrc->xi_cpu = to_cpu;
-			evtchn_cpu_unmask_port(isrc->xi_cpu, isrc->xi_port);
+			xen_intr_cpu_unmask_port(isrc->xi_cpu, isrc->xi_port);
 		}
 	}
 
@@ -1335,7 +1331,8 @@
 xen_intr_get_evtchn_from_port(evtchn_port_t port, xen_intr_handle_t *handlep)
 {
 
-	if (!is_valid_evtchn(port) || port >= NR_EVENT_CHANNELS)
+	/* event channel 0 is reserved, >= NR_EVENT_CHANNELS is invalid */
+	if (port == 0 || port >= NR_EVENT_CHANNELS)
 		return (EINVAL);
 
 	if (handlep == NULL) {