Index: xen-3.3.1-testing/tools/python/xen/xend/XendDomainInfo.py
===================================================================
--- xen-3.3.1-testing.orig/tools/python/xen/xend/XendDomainInfo.py
+++ xen-3.3.1-testing/tools/python/xen/xend/XendDomainInfo.py
@@ -2250,7 +2250,7 @@ class XendDomainInfo:
             vtd_mem = ((vtd_mem + 1023) / 1024) * 1024
 
             # Make sure there's enough RAM available for the domain
-            balloon.free(memory + shadow + vtd_mem)
+            balloon.free(memory + shadow + vtd_mem + 512)
 
             # Set up the shadow memory
             shadow_cur = xc.shadow_mem_control(self.domid, shadow / 1024)