Make sure the minimum shadow allocation is never zero.

Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>

diff -r cba56c13ca3e xen/arch/x86/mm/shadow/common.c
--- a/xen/arch/x86/mm/shadow/common.c	Wed Jan 06 12:45:23 2010 +0000
+++ b/xen/arch/x86/mm/shadow/common.c	Thu Jan 14 12:41:52 2010 +0000
@@ -1244,10 +1244,11 @@
  * instruction, we must be able to map a large number (about thirty) VAs
  * at the same time, which means that to guarantee progress, we must
  * allow for more than ninety allocated pages per vcpu.  We round that
- * up to 128 pages, or half a megabyte per vcpu. */
+ * up to 128 pages, or half a megabyte per vcpu, and add 1 more vcpu's 
+ * worth to make sure we never return zero. */
 static unsigned int shadow_min_acceptable_pages(struct domain *d) 
 {
-    u32 vcpu_count = 0;
+    u32 vcpu_count = 1;
     struct vcpu *v;
 
     for_each_vcpu(d, v)