[PATCH v4 11/11] x86/mm: Fix no-change case in try_preserve_large_page()

From: Toshi Kani
Date: Tue Aug 25 2015 - 17:57:45 EST

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@xxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
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 b64a451..97735f4 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -536,7 +536,7 @@ 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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