xenoprof: avoid division by 0

Signed-off-by: Tim Deegan <tim@xen.org>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>
Committed-by: Jan Beulich <jbeulich@suse.com>

xen/common/xenoprof.c

@@ -193,6 +193,13 @@ static int alloc_xenoprof_struct(
     unsigned max_max_samples;
     int i;
 
+    nvcpu = 0;
+    for_each_vcpu ( d, v )
+        nvcpu++;
+
+    if ( !nvcpu )
+        return -EINVAL;
+
     d->xenoprof = xzalloc(struct xenoprof);
     if ( d->xenoprof == NULL )
     {
@@ -209,10 +216,6 @@ static int alloc_xenoprof_struct(
         return -ENOMEM;
     }
 
-    nvcpu = 0;
-    for_each_vcpu ( d, v )
-        nvcpu++;
-
     bufsize = sizeof(struct xenoprof_buf);
     i = sizeof(struct event_log);
 #ifdef CONFIG_COMPAT