[PATCH 3.16.y-ckt 112/183] ARC: fix page address calculation if PAGE_OFFSET != LINUX_LINK_BASE

[Luis Henriques]

3.16.7-ckt8 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexey Brodkin <abrodkin at synopsys.com>

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)						\
 ({									\