diff -r 819399d0bdb1 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c	Fri Feb 15 14:16:42 2008 +0000
+++ b/xen/arch/x86/mm.c	Mon Feb 18 10:55:18 2008 +0100
@@ -1567,14 +1567,14 @@ static int mod_l3_entry(l3_pgentry_t *pl
             return 0;
         }
 
-        adjust_guest_l3e(nl3e, d);
-
         /* Fast path for identical mapping and presence. */
         if (!l3e_has_changed(ol3e, nl3e, _PAGE_PRESENT))
             return UPDATE_ENTRY(l3, pl3e, ol3e, nl3e, pfn, curr, preserve_ad);
 
         if ( unlikely(!get_page_from_l3e(nl3e, pfn, d)) )
             return 0;
+
+        adjust_guest_l3e(nl3e, d);
 
         if ( unlikely(!UPDATE_ENTRY(l3, pl3e, ol3e, nl3e, pfn, curr,
                                     preserve_ad)) )