[ 3.5.y.z extended stable ] Patch "mm/THP: use pmd_populate() to update the pmd with pgtable_t" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    mm/THP: use pmd_populate() to update the pmd with pgtable_t

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From ffc04465fb757dc41042f4e13e80bcc7f474cb85 Mon Sep 17 00:00:00 2001
From: "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>
Date: Fri, 24 May 2013 15:55:21 -0700
Subject: [PATCH] mm/THP: use pmd_populate() to update the pmd with pgtable_t
 pointer

commit 7c3425123ddfdc5f48e7913ff59d908789712b18 upstream.

We should not use set_pmd_at to update pmd_t with pgtable_t pointer.
set_pmd_at is used to set pmd with huge pte entries and architectures
like ppc64, clear few flags from the pte when saving a new entry.
Without this change we observe bad pte errors like below on ppc64 with
THP enabled.

  BUG: Bad page map in process ld mm=0xc000001ee39f4780 pte:7fc3f37848000001 pmd:c000001ec0000000

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
Cc: Hugh Dickins <hughd at google.com>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Reviewed-by: Andrea Arcangeli <aarcange at redhat.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
[ luis: adjust context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 mm/huge_memory.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 57c4b93..7d0eb9e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1955,7 +1955,12 @@ static void collapse_huge_page(struct mm_struct *mm,
 		pte_unmap(pte);
 		spin_lock(&mm->page_table_lock);
 		BUG_ON(!pmd_none(*pmd));
-		set_pmd_at(mm, address, pmd, _pmd);
+		/*
+		 * We can only use set_pmd_at when establishing
+		 * hugepmds and never for establishing regular pmds that
+		 * points to regular pagetables. Use pmd_populate for that
+		 */
+		pmd_populate(mm, pmd, pmd_pgtable(_pmd));
 		spin_unlock(&mm->page_table_lock);
 		anon_vma_unlock(vma->anon_vma);
 		goto out;
--
1.8.1.2