[3.16.y-ckt stable] Patch "ARC: fix page address calculation if PAGE_OFFSET != LINUX_LINK_BASE" has been added to staging queue

[Luis Henriques]

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

    ARC: fix page address calculation if PAGE_OFFSET != LINUX_LINK_BASE

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt8.

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

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 1b45174c3d5392ffe527e733e539f8885db87ac7 Mon Sep 17 00:00:00 2001
From: Alexey Brodkin <abrodkin at synopsys.com>
Date: Thu, 12 Feb 2015 21:10:11 +0300
Subject: ARC: fix page address calculation if PAGE_OFFSET != LINUX_LINK_BASE

commit 06f34e1c28f3608b0ce5b310e41102d3fe7b65a1 upstream.

We used to calculate page address differently in 2 cases:

1. In virt_to_page(x) we do
 --->8---
 mem_map + (x - CONFIG_LINUX_LINK_BASE) >> PAGE_SHIFT
 --->8---

2. In in pte_page(x) we do
 --->8---
 mem_map + (pte_val(x) - PAGE_OFFSET) >> PAGE_SHIFT
 --->8---

That leads to problems in case PAGE_OFFSET != CONFIG_LINUX_LINK_BASE -
different pages will be selected depending on where and how we calculate
page address.

In particular in the STAR 9000853582 when gdb attempted to read memory
of another process it got improper page in get_user_pages() because this
is exactly one of the places where we search for a page by pte_page().

The fix is trivial - we need to calculate page address similarly in both
cases.

Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com>
Signed-off-by: Vineet Gupta <vgupta at synopsys.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/arc/include/asm/pgtable.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arc/include/asm/pgtable.h b/arch/arc/include/asm/pgtable.h
index 6b0b7f7ef783..7670f33b9ce2 100644
--- a/arch/arc/include/asm/pgtable.h
+++ b/arch/arc/include/asm/pgtable.h
@@ -259,7 +259,8 @@ static inline void pmd_set(pmd_t *pmdp, pte_t *ptep)
 #define pmd_clear(xp)			do { pmd_val(*(xp)) = 0; } while (0)

 #define pte_page(x) (mem_map + \
-		(unsigned long)(((pte_val(x) - PAGE_OFFSET) >> PAGE_SHIFT)))
+		(unsigned long)(((pte_val(x) - CONFIG_LINUX_LINK_BASE) >> \
+				PAGE_SHIFT)))

 #define mk_pte(page, pgprot)						\
 ({									\