[tip:x86/mm] x86/mm: Fix no-change case in try_preserve_large_page()

[tip-bot for Toshi Kani]

Commit-ID:  55696b1f664e52b3036f21631f9c2247b667f587
Gitweb:     http://git.kernel.org/tip/55696b1f664e52b3036f21631f9c2247b667f587
Author:     Toshi Kani <toshi.kani@xxxxxxx>
AuthorDate: Thu, 17 Sep 2015 12:24:24 -0600
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 22 Sep 2015 21:27:33 +0200

x86/mm: Fix no-change case in try_preserve_large_page()

try_preserve_large_page() checks if new_prot is the same as
old_prot.  If so, it simply sets do_split to 0, and returns
with no-operation.  However, old_prot is set as a 4KB pgprot
value while new_prot is a large page pgprot value.

Now that old_prot is initially set from p?d_pgprot() as a
large page pgprot value, fix it by not overwriting old_prot
with a 4KB pgprot value.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Konrad Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Robert Elliot <elliott@xxxxxxx>
Cc: linux-mm@xxxxxxxxx
Link: http://lkml.kernel.org/r/1442514264-12475-12-git-send-email-toshi.kani@xxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 arch/x86/mm/pageattr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index ab9465b..e2621a8 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -518,7 +518,7 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
 	 * up accordingly.
 	 */
 	old_pte = *kpte;
-	old_prot = req_prot = pgprot_large_2_4k(old_prot);
+	req_prot = pgprot_large_2_4k(old_prot);
 
 	pgprot_val(req_prot) &= ~pgprot_val(cpa->mask_clr);
 	pgprot_val(req_prot) |= pgprot_val(cpa->mask_set);
--
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