diff -r 533a8e6cebd0 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c	Sat Jan 12 11:26:04 2008 +0000
+++ b/xen/arch/x86/mm/p2m.c	Tue Jan 15 12:45:14 2008 -0600
@@ -705,8 +705,11 @@ guest_physmap_add_entry(struct domain *d
      * hardware translation limit. This limitation is checked by comparing
      * gfn with 0xfffffUL.
      */
-    if ( paging_mode_hap(d) && (gfn > 0xfffffUL) )
+    if ( paging_mode_hap(d) && (gfn > 0xfffffUL) ) {
+        P2M_ERROR("Nested Paging does not support PAE guests, "\
+                  "on PAE hypervisors using more than 4GB of memory.\n");
         return -EINVAL;
+    }
 #endif
 
     p2m_lock(d);