--- a/xen/common/event_2l.c
+++ b/xen/common/event_2l.c
@@ -61,7 +61,7 @@ static void evtchn_2l_unmask(struct doma
     }
 }
 
-static bool_t evtchn_2l_is_pending(struct domain *d, evtchn_port_t port)
+static bool evtchn_2l_is_pending(const struct domain *d, evtchn_port_t port)
 {
     unsigned int max_ports = BITS_PER_EVTCHN_WORD(d) * BITS_PER_EVTCHN_WORD(d);
 
@@ -69,7 +69,7 @@ static bool_t evtchn_2l_is_pending(struc
     return port < max_ports && test_bit(port, &shared_info(d, evtchn_pending));
 }
 
-static bool_t evtchn_2l_is_masked(struct domain *d, evtchn_port_t port)
+static bool evtchn_2l_is_masked(const struct domain *d, evtchn_port_t port)
 {
     unsigned int max_ports = BITS_PER_EVTCHN_WORD(d) * BITS_PER_EVTCHN_WORD(d);
 
--- a/xen/common/event_fifo.c
+++ b/xen/common/event_fifo.c
@@ -19,7 +19,7 @@
 
 #include <public/event_channel.h>
 
-static inline event_word_t *evtchn_fifo_word_from_port(struct domain *d,
+static inline event_word_t *evtchn_fifo_word_from_port(const struct domain *d,
                                                        unsigned int port)
 {
     unsigned int p, w;
@@ -293,37 +293,25 @@ static void evtchn_fifo_unmask(struct do
         evtchn_fifo_set_pending(v, evtchn);
 }
 
-static bool_t evtchn_fifo_is_pending(struct domain *d, evtchn_port_t port)
+static bool evtchn_fifo_is_pending(const struct domain *d, evtchn_port_t port)
 {
-    event_word_t *word;
-
-    word = evtchn_fifo_word_from_port(d, port);
-    if ( unlikely(!word) )
-        return 0;
+    const event_word_t *word = evtchn_fifo_word_from_port(d, port);
 
-    return test_bit(EVTCHN_FIFO_PENDING, word);
+    return word && test_bit(EVTCHN_FIFO_PENDING, word);
 }
 
-static bool_t evtchn_fifo_is_masked(struct domain *d, evtchn_port_t port)
+static bool_t evtchn_fifo_is_masked(const struct domain *d, evtchn_port_t port)
 {
-    event_word_t *word;
+    const event_word_t *word = evtchn_fifo_word_from_port(d, port);
 
-    word = evtchn_fifo_word_from_port(d, port);
-    if ( unlikely(!word) )
-        return 1;
-
-    return test_bit(EVTCHN_FIFO_MASKED, word);
+    return !word || test_bit(EVTCHN_FIFO_MASKED, word);
 }
 
-static bool_t evtchn_fifo_is_busy(struct domain *d, evtchn_port_t port)
+static bool_t evtchn_fifo_is_busy(const struct domain *d, evtchn_port_t port)
 {
-    event_word_t *word;
-
-    word = evtchn_fifo_word_from_port(d, port);
-    if ( unlikely(!word) )
-        return 0;
+    const event_word_t *word = evtchn_fifo_word_from_port(d, port);
 
-    return test_bit(EVTCHN_FIFO_LINKED, word);
+    return word && test_bit(EVTCHN_FIFO_LINKED, word);
 }
 
 static int evtchn_fifo_set_priority(struct domain *d, struct evtchn *evtchn,
--- a/xen/include/xen/event.h
+++ b/xen/include/xen/event.h
@@ -137,13 +137,13 @@ struct evtchn_port_ops {
     void (*set_pending)(struct vcpu *v, struct evtchn *evtchn);
     void (*clear_pending)(struct domain *d, struct evtchn *evtchn);
     void (*unmask)(struct domain *d, struct evtchn *evtchn);
-    bool_t (*is_pending)(struct domain *d, evtchn_port_t port);
-    bool_t (*is_masked)(struct domain *d, evtchn_port_t port);
+    bool (*is_pending)(const struct domain *d, evtchn_port_t port);
+    bool (*is_masked)(const struct domain *d, evtchn_port_t port);
     /*
      * Is the port unavailable because it's still being cleaned up
      * after being closed?
      */
-    bool_t (*is_busy)(struct domain *d, evtchn_port_t port);
+    bool (*is_busy)(const struct domain *d, evtchn_port_t port);
     int (*set_priority)(struct domain *d, struct evtchn *evtchn,
                         unsigned int priority);
     void (*print_state)(struct domain *d, const struct evtchn *evtchn);
@@ -174,23 +174,23 @@ static inline void evtchn_port_unmask(st
     d->evtchn_port_ops->unmask(d, evtchn);
 }
 
-static inline bool_t evtchn_port_is_pending(struct domain *d,
-                                            evtchn_port_t port)
+static inline bool evtchn_port_is_pending(const struct domain *d,
+                                          evtchn_port_t port)
 {
     return d->evtchn_port_ops->is_pending(d, port);
 }
 
-static inline bool_t evtchn_port_is_masked(struct domain *d,
-                                           evtchn_port_t port)
+static inline bool evtchn_port_is_masked(const struct domain *d,
+                                         evtchn_port_t port)
 {
     return d->evtchn_port_ops->is_masked(d, port);
 }
 
-static inline bool_t evtchn_port_is_busy(struct domain *d, evtchn_port_t port)
+static inline bool evtchn_port_is_busy(const struct domain *d,
+                                       evtchn_port_t port)
 {
-    if ( d->evtchn_port_ops->is_busy )
-        return d->evtchn_port_ops->is_busy(d, port);
-    return 0;
+    return d->evtchn_port_ops->is_busy &&
+           d->evtchn_port_ops->is_busy(d, port);
 }
 
 static inline int evtchn_port_set_priority(struct domain *d,
