Patch "powerpc/mm: Recompute hash value after a failed update" has been added to the 4.2-stable tree

Patch "powerpc/mm: Recompute hash value after a failed update" has been added to the 4.2-stable tree

[gregkh]

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

    powerpc/mm: Recompute hash value after a failed update

to the 4.2-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:
     powerpc-mm-recompute-hash-value-after-a-failed-update.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 36b35d5d807b7e57aff7d08e63de8b17731ee211 Mon Sep 17 00:00:00 2001
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Date: Tue, 15 Sep 2015 12:30:08 +0530
Subject: powerpc/mm: Recompute hash value after a failed update

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

commit 36b35d5d807b7e57aff7d08e63de8b17731ee211 upstream.

If we had secondary hash flag set, we ended up modifying hash value in
the updatepp code path. Hence with a failed updatepp we will be using
a wrong hash value for the following hash insert. Fix this by
recomputing hash before insert.

Without this patch we can end up with using wrong slot number in linux
pte. That can result in us missing an hash pte update or invalidate
which can cause memory corruption or even machine check.

Fixes: 6d492ecc6489 ("powerpc/THP: Add code to handle HPTE faults for hugepages")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Reviewed-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/powerpc/mm/hugepage-hash64.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/powerpc/mm/hugepage-hash64.c
+++ b/arch/powerpc/mm/hugepage-hash64.c
@@ -85,7 +85,6 @@ int __hash_page_thp(unsigned long ea, un
 	BUG_ON(index >= 4096);
 
 	vpn = hpt_vpn(ea, vsid, ssize);
-	hash = hpt_hash(vpn, shift, ssize);
 	hpte_slot_array = get_hpte_slot_array(pmdp);
 	if (psize == MMU_PAGE_4K) {
 		/*
@@ -101,6 +100,7 @@ int __hash_page_thp(unsigned long ea, un
 	valid = hpte_valid(hpte_slot_array, index);
 	if (valid) {
 		/* update the hpte bits */
+		hash = hpt_hash(vpn, shift, ssize);
 		hidx =  hpte_hash_index(hpte_slot_array, index);
 		if (hidx & _PTEIDX_SECONDARY)
 			hash = ~hash;
@@ -126,6 +126,7 @@ int __hash_page_thp(unsigned long ea, un
 	if (!valid) {
 		unsigned long hpte_group;
 
+		hash = hpt_hash(vpn, shift, ssize);
 		/* insert new entry */
 		pa = pmd_pfn(__pmd(old_pmd)) << PAGE_SHIFT;
 		new_pmd |= _PAGE_HASHPTE;


Patches currently in stable-queue which might be from aneesh.kumar@linux.vnet.ibm.com are

queue-4.2/powerpc-mm-recompute-hash-value-after-a-failed-update.patch
queue-4.2/powerpc-mm-fix-pte_pagesize_index-crash-on-4k-w-64k-hash.patch