[PATCH 6 of 8] x86: clarify use of _PAGE_CHG_MASK

[Jeremy Fitzhardinge <jeremy@goop.org>]

_PAGE_CHG_MASK is defined as the set of bits not updated by
pte_modify(); specifically, the pfn itself, and the Accessed and Dirty
bits (which are updated by hardware).

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
 include/asm-x86/pgtable.h |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/include/asm-x86/pgtable.h b/include/asm-x86/pgtable.h
--- a/include/asm-x86/pgtable.h
+++ b/include/asm-x86/pgtable.h
@@ -58,6 +58,7 @@
 #define _KERNPG_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED |	\
 			 _PAGE_DIRTY)
 
+/* Set of bits not changed in pte_modify */
 #define _PAGE_CHG_MASK	(PTE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY)
 
 #define _PAGE_CACHE_MASK	(_PAGE_PCD | _PAGE_PWT)
@@ -285,11 +286,8 @@
 {
 	pteval_t val = pte_val(pte);
 
-	/*
-	 * Chop off the NX bit (if present), and add the NX portion of
-	 * the newprot (if present):
-	 */
-	val &= _PAGE_CHG_MASK & ~_PAGE_NX;
+	/* Extract unchanged bits from pte */
+	val &= _PAGE_CHG_MASK;
 	val |= pgprot_val(newprot) & __supported_pte_mask;
 
 	return __pte(val);