diff -r d19deb173503 linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h
--- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h	Fri Nov 10 15:27:22 2006 +0000
+++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h	Fri Nov 10 21:37:45 2006 -0600
@@ -127,10 +127,17 @@ static inline maddr_t phys_to_machine(pa
 	machine = (machine << PAGE_SHIFT) | (phys & ~PAGE_MASK);
 	return machine;
 }
+
 static inline paddr_t machine_to_phys(maddr_t machine)
 {
+	/*
+	 * In PAE mode, the NX bit needs to be dealt with in the value
+	 * passed to mfn_to_pfn(). On x86_64, we need to mask it off,
+	 * but for i386 the conversion to ulong for the argument will
+	 * clip it off.
+	 */
 	paddr_t phys = mfn_to_pfn(machine >> PAGE_SHIFT);
-	phys = (phys << PAGE_SHIFT) | (machine & ~PAGE_MASK);
+	phys = (phys << PAGE_SHIFT) | (machine & ~PHYSICAL_PAGE_MASK);
 	return phys;
 }
 
diff -r d19deb173503 linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h
--- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h	Fri Nov 10 15:27:22 2006 +0000
+++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h	Sat Nov 11 03:14:00 2006 -0600
@@ -5,6 +5,16 @@
 #define PAGE_SHIFT	12
 #define PAGE_SIZE	(1UL << PAGE_SHIFT)
 #define PAGE_MASK	(~(PAGE_SIZE-1))
+
+#ifdef CONFIG_X86_PAE
+#define __PHYSICAL_MASK_SHIFT	36
+#define __PHYSICAL_MASK		((1ULL << __PHYSICAL_MASK_SHIFT) - 1)
+#define PHYSICAL_PAGE_MASK	(~((1ULL << PAGE_SHIFT) - 1) & __PHYSICAL_MASK)
+#else
+#define __PHYSICAL_MASK_SHIFT	32
+#define __PHYSICAL_MASK		(~0UL)
+#define PHYSICAL_PAGE_MASK	(PAGE_MASK & __PHYSICAL_MASK)
+#endif
 
 #define LARGE_PAGE_MASK (~(LARGE_PAGE_SIZE-1))
 #define LARGE_PAGE_SIZE (1UL << PMD_SHIFT)
diff -r d19deb173503 linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h
--- a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h	Fri Nov 10 15:27:22 2006 +0000
+++ b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h	Fri Nov 10 21:36:35 2006 -0600
@@ -122,8 +122,8 @@ static inline maddr_t phys_to_machine(pa
 
 static inline paddr_t machine_to_phys(maddr_t machine)
 {
-	paddr_t phys = mfn_to_pfn(machine >> PAGE_SHIFT);
-	phys = (phys << PAGE_SHIFT) | (machine & ~PAGE_MASK);
+	paddr_t phys = mfn_to_pfn((machine & PHYSICAL_PAGE_MASK) >> PAGE_SHIFT);
+	phys = (phys << PAGE_SHIFT) | (machine & ~PHYSICAL_PAGE_MASK);
 	return phys;
 }
 
diff -r d19deb173503 linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h
--- a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h	Fri Nov 10 15:27:22 2006 +0000
+++ b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h	Fri Nov 10 21:36:35 2006 -0600
@@ -33,6 +33,13 @@
 #define PAGE_SIZE	(1UL << PAGE_SHIFT)
 #endif
 #define PAGE_MASK	(~(PAGE_SIZE-1))
+
+/* See Documentation/x86_64/mm.txt for a description of the memory map. */
+#define __PHYSICAL_MASK_SHIFT	46
+#define __PHYSICAL_MASK		((1UL << __PHYSICAL_MASK_SHIFT) - 1)
+#define __VIRTUAL_MASK_SHIFT	48
+#define __VIRTUAL_MASK		((1UL << __VIRTUAL_MASK_SHIFT) - 1)
+
 #define PHYSICAL_PAGE_MASK	(~(PAGE_SIZE-1) & __PHYSICAL_MASK)
 
 #define THREAD_ORDER 1 
@@ -162,12 +169,6 @@ static inline pgd_t __pgd(unsigned long 
 
 /* to align the pointer to the (next) page boundary */
 #define PAGE_ALIGN(addr)	(((addr)+PAGE_SIZE-1)&PAGE_MASK)
-
-/* See Documentation/x86_64/mm.txt for a description of the memory map. */
-#define __PHYSICAL_MASK_SHIFT	46
-#define __PHYSICAL_MASK		((1UL << __PHYSICAL_MASK_SHIFT) - 1)
-#define __VIRTUAL_MASK_SHIFT	48
-#define __VIRTUAL_MASK		((1UL << __VIRTUAL_MASK_SHIFT) - 1)
 
 #define KERNEL_TEXT_SIZE  (40UL*1024*1024)
 #define KERNEL_TEXT_START 0xffffffff80000000UL