x86: fix pte_modify() bug

fix sign extension bug in PTE_MASK / _PTE_CHG_MASK.

this resolves the following bootup crash on PAE systems:

[   94.710726] init[1]: segfault at 00000004 ip 49471cbb sp bff0c6c0 error 4
[   94.717764] init[1]: segfault at 00000004 ip 49471cbb sp bff0c6c0 error 4
[   94.724772] init[1]: segfault at 00000004 ip 49471cbb sp bff0c6c0 error 4
[   94.731777] init[1]: segfault at 00000004 ip 49471cbb sp bff0c6c0 error 4
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

include/asm-x86/page.h

@@ -11,7 +11,7 @@
 #ifdef __KERNEL__
 
 #define PHYSICAL_PAGE_MASK	(PAGE_MASK & __PHYSICAL_MASK)
-#define PTE_MASK		PHYSICAL_PAGE_MASK
+#define PTE_MASK		(_AT(long, PHYSICAL_PAGE_MASK))
 
 #define LARGE_PAGE_SIZE		(_AC(1,UL) << PMD_SHIFT)
 #define LARGE_PAGE_MASK		(~(LARGE_PAGE_SIZE-1))