[PATCH 2/2] ARM: memory: define TASK_UNMAPPED_BASE in terms of TASK_SIZE

[Will Deacon]

TASK_UNMAPPED_BASE is defined directly in terms of PAGE_OFFSET, which is
confusing given that the modules area sits between here and TASK_SIZE
and is not available for user allocations.

This patch defines TASK_UNMAPPED_BASE in terms of TASK_SIZE instead and
fixes a bug introduced by 394ef6403abc ("mm: use vm_unmapped_area() on
arm architecture") whereby TASK_UNMAPPED_BASE is no longer page-aligned
for bottom-up mmap, causing get_unmapped_area to choke on misaligned
addresses.

Reported-by: Christoffer Dall <cdall at cs.columbia.edu>
Signed-off-by: Will Deacon <will.deacon at arm.com>
---
 arch/arm/include/asm/memory.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index a0fd518..255a01b 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -37,7 +37,7 @@
  */
 #define PAGE_OFFSET		UL(CONFIG_PAGE_OFFSET)
 #define TASK_SIZE		(UL(CONFIG_PAGE_OFFSET) - UL(SZ_16M))
-#define TASK_UNMAPPED_BASE	(UL(CONFIG_PAGE_OFFSET) / 3)
+#define TASK_UNMAPPED_BASE	((TASK_SIZE / 3) & ~UL(SZ_16M - 1))
 
 /*
  * The maximum size of a 26-bit user space task.
-- 
1.8.0