linux-kernel - Re: [PATCH] ARM: memblock limit must be pmd-aligned

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Date:   Mon, 26 Jun 2017 16:43:58 -0700
From:   Laura Abbott <labbott@...hat.com>
To:     Doug Berger <opendmb@...il.com>, linux@...linux.org.uk
Cc:     ard.biesheuvel@...aro.org, nicolas.pitre@...aro.org,
        tixy@...aro.org, f.fainelli@...il.com, keescook@...omium.org,
        marc.zyngier@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: memblock limit must be pmd-aligned

On 06/26/2017 10:23 AM, Doug Berger wrote:
> 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.
> 
> However, 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.
> 
> The pmd containing arm_lowmem_limit is cleared by prepare_page_table()
> and without this commit it is possible for early_alloc() to allocate
> unmapped memory in that range when mapping the lowmem.
> 

Do you have an example system or configuration where you see this
crash?

Thanks,
Laura

> Signed-off-by: Doug Berger <opendmb@...il.com>
> ---
>  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 31af3cb59a60..2ae4f9c9d757 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -1226,7 +1226,7 @@ void __init adjust_lowmem_bounds(void)
>  	if (memblock_limit)
>  		memblock_limit = round_down(memblock_limit, PMD_SIZE);
>  	if (!memblock_limit)
> -		memblock_limit = arm_lowmem_limit;
> +		memblock_limit = round_down(arm_lowmem_limit, PMD_SIZE);
>  
>  	if (!IS_ENABLED(CONFIG_HIGHMEM) || cache_is_vipt_aliasing()) {
>  		if (memblock_end_of_DRAM() > arm_lowmem_limit) {
>