diff -r 99559bbc4ecf xen/include/asm-x86/x86_64/page.h
--- a/xen/include/asm-x86/x86_64/page.h	Wed Aug 30 13:48:25 2006 +0800
+++ b/xen/include/asm-x86/x86_64/page.h	Wed Aug 30 14:02:03 2006 +0800
@@ -75,10 +75,13 @@ typedef l4_pgentry_t root_pgentry_t;
 #define _PAGE_NX_BIT (1U<<23)
 #define _PAGE_NX     (cpu_has_nx ? _PAGE_NX_BIT : 0U)
 
-#define L1_DISALLOW_MASK BASE_DISALLOW_MASK
-#define L2_DISALLOW_MASK BASE_DISALLOW_MASK
-#define L3_DISALLOW_MASK (BASE_DISALLOW_MASK | 0x180U /* must-be-zero */)
-#define L4_DISALLOW_MASK (BASE_DISALLOW_MASK | 0x180U /* must-be-zero */)
+/* From spec, the [62:52] is software available for em64t */
+#define BASE_DISALLOW_MASK_64 ((0xFF000180U | _PAGE_GNTTAB) & ~_PAGE_NX)
+
+#define L1_DISALLOW_MASK BASE_DISALLOW_MASK_64
+#define L2_DISALLOW_MASK BASE_DISALLOW_MASK_64
+#define L3_DISALLOW_MASK (BASE_DISALLOW_MASK_64 | 0x180U /* must-be-zero */)
+#define L4_DISALLOW_MASK (BASE_DISALLOW_MASK_64 | 0x180U /* must-be-zero */)
 
 #define PAGE_HYPERVISOR         (__PAGE_HYPERVISOR         | _PAGE_GLOBAL)
 #define PAGE_HYPERVISOR_NOCACHE (__PAGE_HYPERVISOR_NOCACHE | _PAGE_GLOBAL)