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Subject[patch 21/29] x86: NX bit handling in change_page_attr()
2.6.23-stable review patch.  If anyone has any objections, please let us

From: Huang, Ying <>
patch 84e0fdb1754d066dd0a8b257de7299f392d1e727 in mainline.

x86: NX bit handling in change_page_attr()

This patch fixes a bug of change_page_attr/change_page_attr_addr on
Intel x86_64 CPUs. After changing page attribute to be executable with
these functions, the page remains un-executable on Intel x86_64 CPU.
Because on Intel x86_64 CPU, only if the "NX" bits of all four level
page tables are cleared, the corresponding page is executable (refer to
section 4.13.2 of Intel 64 and IA-32 Architectures Software Developer's
Manual). So, the bug is fixed through clearing the "NX" bit of PMD when
splitting the huge PMD.

Signed-off-by: Huang Ying <>
Cc: Andi Kleen <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Ingo Molnar <>
Signed-off-by: Thomas Gleixner <>
Signed-off-by: Greg Kroah-Hartman <>

arch/x86_64/mm/pageattr.c | 1 +
1 file changed, 1 insertion(+)
--- a/arch/x86_64/mm/pageattr.c
+++ b/arch/x86_64/mm/pageattr.c
@@ -148,6 +148,7 @@ __change_page_attr(unsigned long address
split = split_large_page(address, prot, ref_prot2);
if (!split)
return -ENOMEM;
+ pgprot_val(ref_prot2) &= ~_PAGE_NX;
set_pte(kpte, mk_pte(split, ref_prot2));
kpte_page = split;
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