Subject: [PATCH] arm: mm: fix lowmem virtual address range check

From: [email-masked] (Will Deacon)
Date: Wed, 14 May 2014 11:11:37 +0100

On Wed, May 14, 2014 at 07:03:59AM +0100, Wang Nan wrote:
> This patch makes sure the argument of __phys_to_virt is a valid physical
> address when clear lowmem memory maps.
> 
> The last few lines prepare_page_table() clear page mapping in the gap
> between largest low physical memory and the upper bound of lowmem. It
> uses __phys_to_virt(end) to calculate virtual address from where the
> clearing start.
> 
> However, if the platform uses private nonliner __phys_to_virt(), 'end'
> may goes into another mapping region.
> 
> This patch uses __phys_to_virt(end - 1) + 1 for insurance purposes.
> 
> Signed-off-by: Wang Nan <[email-masked]>
> Cc: Geng Hui <[email-masked]>
> Cc: Will Deacon <[email-masked]>
> ---
>  arch/arm/mm/mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index b68c6b2..87340ee 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -1217,7 +1217,7 @@ static inline void prepare_page_table(void)
>  	 * Clear out all the kernel space mappings, except for the first
>  	 * memory bank, up to the vmalloc region.
>  	 */
> -	for (addr = __phys_to_virt(end);
> +	for (addr = __phys_to_virt(end - 1) + 1;
>  	     addr < VMALLOC_START; addr += PMD_SIZE)
>  		pmd_clear(pmd_off_k(addr));

This looks correct to me, but I'd be interested to know which platform this
is falling over on. Only realview seems to override __phys_to_virt and I
don't think we want to add more of that if we can help it.

Will