Patch "ARC: mm: don't loose PTE_SPECIAL in pte_modify()" has been added to the 4.7-stable tree

Patch "ARC: mm: don't loose PTE_SPECIAL in pte_modify()" has been added to the 4.7-stable tree

[gregkh]

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

    ARC: mm: don't loose PTE_SPECIAL in pte_modify()

to the 4.7-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:
     arc-mm-don-t-loose-pte_special-in-pte_modify.patch
and it can be found in the queue-4.7 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 3925a16ae980c79d1a8fd182d7f9487da1edd4dc Mon Sep 17 00:00:00 2001
From: Vineet Gupta <vgupta@synopsys.com>
Date: Thu, 28 Jul 2016 11:35:50 -0700
Subject: ARC: mm: don't loose PTE_SPECIAL in pte_modify()

From: Vineet Gupta <vgupta@synopsys.com>

commit 3925a16ae980c79d1a8fd182d7f9487da1edd4dc upstream.

LTP madvise05 was generating mm splat

| [ARCLinux]# /sd/ltp/testcases/bin/madvise05
| BUG: Bad page map in process madvise05  pte:80e08211 pmd:9f7d4000
| page:9fdcfc90 count:1 mapcount:-1 mapping:  (null) index:0x0 flags: 0x404(referenced|reserved)
| page dumped because: bad pte
| addr:200b8000 vm_flags:00000070 anon_vma:  (null) mapping:  (null) index:1005c
| file:  (null) fault:  (null) mmap:  (null) readpage:  (null)
| CPU: 2 PID: 6707 Comm: madvise05

And for newer kernels, the system was rendered unusable afterwards.

The problem was mprotect->pte_modify() clearing PTE_SPECIAL (which is
set to identify the special zero page wired to the pte).
When pte was finally unmapped, special casing for zero page was not
done, and instead it was treated as a "normal" page, tripping on the
map counts etc.

This fixes ARC STAR 9001053308

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arc/include/asm/pgtable.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arc/include/asm/pgtable.h
+++ b/arch/arc/include/asm/pgtable.h
@@ -110,7 +110,7 @@
 #define ___DEF (_PAGE_PRESENT | _PAGE_CACHEABLE)
 
 /* Set of bits not changed in pte_modify */
-#define _PAGE_CHG_MASK	(PAGE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY)
+#define _PAGE_CHG_MASK	(PAGE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_SPECIAL)
 
 /* More Abbrevaited helpers */
 #define PAGE_U_NONE     __pgprot(___DEF)


Patches currently in stable-queue which might be from vgupta@synopsys.com are

queue-4.7/arc-mm-don-t-loose-pte_special-in-pte_modify.patch
queue-4.7/arc-dma-fix-address-translation-in-arc_dma_free.patch