x86: use PTE_MASK rather than ad-hoc mask

Use ~PTE_MASK to extract the non-pfn parts of the pte (ie, the pte
flags), rather than constructing an ad-hoc mask.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Tested-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-x86/pgtable.h

@@ -305,7 +305,7 @@ static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
 	return __pgprot(preservebits | addbits);
 }
 
-#define pte_pgprot(x) __pgprot(pte_val(x) & (0xfff | _PAGE_NX))
+#define pte_pgprot(x) __pgprot(pte_val(x) & ~PTE_MASK)
 
 #define canon_pgprot(p) __pgprot(pgprot_val(p) & __supported_pte_mask)