Patch "ARM: 8579/1: mm: Fix definition of pmd_mknotpresent" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ARM: 8579/1: mm: Fix definition of pmd_mknotpresent

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     arm-8579-1-mm-fix-definition-of-pmd_mknotpresent.patch

and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Steve Capper <[email protected]>
Date: Tue, 7 Jun 2016 17:58:06 +0100
Subject: ARM: 8579/1: mm: Fix definition of pmd_mknotpresent

From: Steve Capper <[email protected]>

commit 56530f5d2ddc9b9fade7ef8db9cb886e9dc689b5 upstream.

Currently pmd_mknotpresent will use a zero entry to respresent an invalidated pmd.

Unfortunately this definition clashes with pmd_none, thus it is possible for a race condition to occur if zap_pmd_range sees pmd_none whilst __split_huge_pmd_locked is running too with pmdp_invalidate just called.

This patch fixes the race condition by modifying pmd_mknotpresent to create non-zero faulting entries (as is done in other architectures), removing the ambiguity with pmd_none.

[[email protected]: using L_PMD_SECT_VALID instead of PMD_TYPE_SECT]

---
 arch/arm/include/asm/pgtable-3level.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -258,10 +258,10 @@ PMD_BIT_FUNC(mkyoung,   |= PMD_SECT_AF);
 #define pfn_pmd(pfn,prot)	(__pmd(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
 #define mk_pmd(page,prot)	pfn_pmd(page_to_pfn(page),prot)
 
-/* represent a notpresent pmd by zero, this is used by pmdp_invalidate */
+/* represent a notpresent pmd by faulting entry, this is used by pmdp_invalidate */
 static inline pmd_t pmd_mknotpresent(pmd_t pmd)
 {
-	return __pmd(0);
+	return __pmd(pmd_val(pmd) & ~L_PMD_SECT_VALID);
 }
 
 static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/arm-8579-1-mm-fix-definition-of-pmd_mknotpresent.patch