Re: [PATCH] ARM: ensure memblock-limit is pmd-aligned

[Doug Berger]

On 06/29/2017 04:16 AM, Mark Rutland wrote:
> On Tue, Jun 27, 2017 at 10:33:29AM -0700, Doug Berger wrote:
>> The pmd containing memblock_limit is cleared by prepare_page_table()
>> which creates the opportunity for early_alloc() to allocate unmapped
>> memory if memblock_limit is not pmd aligned causing a boot-time hang.
>>
>> Commit 965278dcb8ab ("ARM: 8356/1: mm: handle non-pmd-aligned end of RAM")
>> attempted to resolve this problem, but there is a path through the
>> adjust_lowmem_bounds() routine where if all memory regions start and
>> end on pmd-aligned addresses the memblock_limit will be set to
>> arm_lowmem_limit.
>>
>> Since arm_lowmem_limit can be affected by the vmalloc early parameter,
>> the value of arm_lowmem_limit may not be pmd-aligned. This commit
>> corrects this oversight such that memblock_limit is always rounded
>> down to pmd-alignment.
>>
>> Fixes: 965278dcb8ab ("ARM: 8356/1: mm: handle non-pmd-aligned end of RAM")
>> Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
>> Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
> 
> As a minor nit, it would be better for the title to be something like
> "ARM: ensure memblock-limit is pmd-aligned", but either way:
> 
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
> 
> Assuming Russell doesn't have any furhter comments, this looks good to
> drop into the patch system. See:
> 
>   http://www.arm.linux.org.uk/developer/patches/info.php
> 
> ... for instructions on how to send patches there.
> 
> Thanks,
> Mark.
> 

I modified the title as suggested and it has been submitted as 8685/1.

Thanks!

>> ---
>> Changes for v2:
>>  - Cleaner equivalent implementation suggested by Mark Rutland
>>  - Revised description to better capture the history
>>
>>  arch/arm/mm/mmu.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
>> index 31af3cb59a60..e46a6a446cdd 100644
>> --- a/arch/arm/mm/mmu.c
>> +++ b/arch/arm/mm/mmu.c
>> @@ -1218,15 +1218,15 @@ void __init adjust_lowmem_bounds(void)
>>  
>>  	high_memory = __va(arm_lowmem_limit - 1) + 1;
>>  
>> +	if (!memblock_limit)
>> +		memblock_limit = arm_lowmem_limit;
>> +
>>  	/*
>>  	 * Round the memblock limit down to a pmd size.  This
>>  	 * helps to ensure that we will allocate memory from the
>>  	 * last full pmd, which should be mapped.
>>  	 */
>> -	if (memblock_limit)
>> -		memblock_limit = round_down(memblock_limit, PMD_SIZE);
>> -	if (!memblock_limit)
>> -		memblock_limit = arm_lowmem_limit;
>> +	memblock_limit = round_down(memblock_limit, PMD_SIZE);
>>  
>>  	if (!IS_ENABLED(CONFIG_HIGHMEM) || cache_is_vipt_aliasing()) {
>>  		if (memblock_end_of_DRAM() > arm_lowmem_limit) {
>> -- 
>> 2.13.0
>>
>>
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