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

[Nicolas Pitre]

On Wed, 30 Jan 2013, Will Deacon wrote:

> 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))

Please round this up not down.  In most cases, TASK_SIZE is 0xbf000000 
which is not nicely divisible by 3, unlike PAGE_OFFSET was.  By rounding 
up you get a nice 0x40000000 as before.


Nicolas