[PATCH 4/4][Zesty SRU] mm/ksm: handle protnone saved writes when making page write protect

[Seth Forshee]

From: "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1674838

Without this KSM will consider the page write protected, but a numa
fault can later mark the page writable.  This can result in memory
corruption.

Link: http://lkml.kernel.org/r/1487498625-10891-3-git-send-email-aneesh.kumar@linux.vnet.ibm.com
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(backported from commit 595cd8f256d24face93b2722927ec9c980419c26)
Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
---
 include/asm-generic/pgtable.h | 8 ++++++++
 mm/ksm.c                      | 9 +++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index b6f3a8a4b738..8c8ba48bef0b 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -200,6 +200,10 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
 #define pte_mk_savedwrite pte_mkwrite
 #endif
 
+#ifndef pte_clear_savedwrite
+#define pte_clear_savedwrite pte_wrprotect
+#endif
+
 #ifndef pmd_savedwrite
 #define pmd_savedwrite pmd_write
 #endif
@@ -208,6 +212,10 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
 #define pmd_mk_savedwrite pmd_mkwrite
 #endif
 
+#ifndef pmd_clear_savedwrite
+#define pmd_clear_savedwrite pmd_wrprotect
+#endif
+
 #ifndef __HAVE_ARCH_PMDP_SET_WRPROTECT
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static inline void pmdp_set_wrprotect(struct mm_struct *mm,
diff --git a/mm/ksm.c b/mm/ksm.c
index fed4afd8293b..099dfa45d596 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -878,7 +878,8 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 	if (!ptep)
 		goto out_mn;
 
-	if (pte_write(*ptep) || pte_dirty(*ptep)) {
+	if (pte_write(*ptep) || pte_dirty(*ptep) ||
+	    (pte_protnone(*ptep) && pte_savedwrite(*ptep))) {
 		pte_t entry;
 
 		swapped = PageSwapCache(page);
@@ -903,7 +904,11 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 		}
 		if (pte_dirty(entry))
 			set_page_dirty(page);
-		entry = pte_mkclean(pte_wrprotect(entry));
+
+		if (pte_protnone(entry))
+			entry = pte_mkclean(pte_clear_savedwrite(entry));
+		else
+			entry = pte_mkclean(pte_wrprotect(entry));
 		set_pte_at_notify(mm, addr, ptep, entry);
 	}
 	*orig_pte = *ptep;
-- 
2.7.4