From 276ef5758e80ccaf3242026fe5a2dd0c5c686108 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Date: Thu, 29 Nov 2012 14:17:36 +1100
Subject: [PATCH] thp: change_huge_pmd(): keep huge zero page write-protected

We want to get page fault on write attempt to huge zero page, so let's
keep it write-protected.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/huge_memory.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index edc1869c532d..12dc04046b9f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1433,6 +1433,8 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 		pmd_t entry;
 		entry = pmdp_get_and_clear(mm, addr, pmd);
 		entry = pmd_modify(entry, newprot);
+		if (is_huge_zero_pmd(entry))
+			entry = pmd_wrprotect(entry);
 		set_pmd_at(mm, addr, pmd, entry);
 		spin_unlock(&vma->vm_mm->page_table_lock);
 		ret = 1;
-- 
2.39.5