diff -r d8fd24b43080 linux-2.6-xen-sparse/include/asm-xen/asm-x86_64/page.h
--- a/linux-2.6-xen-sparse/include/asm-xen/asm-x86_64/page.h	Mon Aug 22 10:18:14 2005
+++ b/linux-2.6-xen-sparse/include/asm-xen/asm-x86_64/page.h	Thu Aug 25 23:02:23 2005
@@ -64,7 +64,28 @@
 /**** MACHINE <-> PHYSICAL CONVERSION MACROS ****/
 extern u32 *phys_to_machine_mapping;
 #define pfn_to_mfn(_pfn) ((unsigned long) phys_to_machine_mapping[(unsigned int)(_pfn)])
-#define mfn_to_pfn(_mfn) ((unsigned long) machine_to_phys_mapping[(unsigned int)(_mfn)])
+
+static inline unsigned long mfn_to_pfn(unsigned long mfn)
+{
+	unsigned int pfn;
+	u32* addr = &machine_to_phys_mapping[(unsigned int)(mfn)];
+
+	__asm__ __volatile__(
+		"1:	movl %1,%k0\n"
+		"2:\n"
+		".section .fixup,\"ax\"\n"
+		"3:	movl %2,%k0\n"
+		"	jmp 2b\n"
+		".previous\n"
+		".section __ex_table,\"a\"\n"
+		"	.align 8\n"
+		"	.quad 1b,3b\n"
+		".previous"
+		: "=r"(pfn)
+		: "m"(*addr), "i"(0x55555555));
+
+	return (unsigned long)pfn;
+}
 
 /* Definitions for machine and pseudophysical addresses. */
 typedef unsigned long paddr_t;