Subject: Re: [PATCH] ARM: memblock limit must be pmd-aligned
To: Doug Berger <opendmb@gmail.com>, linux@armlinux.org.uk
Cc: ard.biesheuvel@linaro.org, nicolas.pitre@linaro.org, tixy@linaro.org,
        f.fainelli@gmail.com, keescook@chromium.org, marc.zyngier@arm.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <20170626172315.26369-1-opendmb@gmail.com>
From: Laura Abbott <labbott@redhat.com>
Message-ID: <48116220-b89b-7413-ea62-c78dfb0594a2@redhat.com>
Date: Mon, 26 Jun 2017 16:43:58 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.1.0
MIME-Version: 1.0
In-Reply-To: <20170626172315.26369-1-opendmb@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1455
Lines: 40

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@gmail.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) {
>