[PATCH] xen/events: fix get_global_virq_handler() usage without hardware domain

[Juergen Gross <jgross@xxxxxxxx>]

Some use cases of get_global_virq_handler() didn't account for the
case of running without hardware domain.

Fix that by testing get_global_virq_handler() returning NULL where
needed (e.g. when directly dereferencing the result).

Fixes: 980822c5edd1 ("xen/events: allow setting of global virq handler only for 
unbound virqs")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/common/event_channel.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index 4ee6b6b4ce..fa83d9dd1a 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -1036,7 +1036,9 @@ int set_global_virq_handler(struct domain *d, uint32_t 
virq)
     {
         old = global_virq_handlers[virq];
         hdl = get_global_virq_handler(virq);
-        if ( hdl != d )
+        if ( !hdl )
+            global_virq_handlers[virq] = d;
+        else if ( hdl != d )
         {
             read_lock(&hdl->event_lock);
 
@@ -1091,7 +1093,7 @@ struct domain *lock_dom_exc_handler(void)
     struct domain *d;
 
     d = get_global_virq_handler(VIRQ_DOM_EXC);
-    if ( unlikely(!get_domain(d)) )
+    if ( unlikely(!d || !get_domain(d)) )
         return NULL;
 
     read_lock(&d->event_lock);
-- 
2.43.0