Index: xen-4.1.1-testing/tools/python/xen/xend/XendDomainInfo.py
===================================================================
--- xen-4.1.1-testing.orig/tools/python/xen/xend/XendDomainInfo.py
+++ xen-4.1.1-testing/tools/python/xen/xend/XendDomainInfo.py
@@ -2926,7 +2926,7 @@ class XendDomainInfo:
 
             self.guest_bitsize = self.image.getBitSize()
             # Make sure there's enough RAM available for the domain
-            balloon.free(memory + shadow + vtd_mem, self)
+            balloon.free(memory + shadow + vtd_mem + 512, self)
 
             # Set up the shadow memory
             shadow_cur = xc.shadow_mem_control(self.domid, shadow / 1024)