Re: [ 058/128] ARM: 7628/1: head.S: map one extra section for theATAG/DTB area

[Ben Hutchings]

On Sun, 2013-02-03 at 15:47 +0100, Ben Hutchings wrote:
> 3.2-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
> 
> commit 6f16f4998f98e42e3f2dedf663cfb691ff0324af upstream.
> 
> We currently use a temporary 1MB section aligned to a 1MB boundary for
> mapping the provided device tree until the final page table is created.
> However, if the device tree happens to cross that 1MB boundary, the end
> of it remains unmapped and the kernel crashes when it attempts to access
> it.  Given no restriction on the location of that DTB, it could end up
> with only a few bytes mapped at the end of a section.
> 
> Solve this issue by mapping two consecutive sections.
> 
> Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxx>
> Tested-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> Tested-by: Tomasz Figa <t.figa@xxxxxxxxxxx>
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
> [bwh: Backported to 3.2:
>  - Adjust context
>  - The mapping is not conditional; drop the 'ne' suffixes]
> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>

I haven't been able to test this and would really appreciate an expert
review.

Ben.

> ---
>  arch/arm/kernel/head.S |    3 +++
>  1 file changed, 3 insertions(+)
> 
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -221,6 +221,7 @@ __create_page_tables:
>  	/*
>  	 * Then map boot params address in r2 or
>  	 * the first 1MB of ram if boot params address is not specified.
> +	 * We map 2 sections in case the ATAGs/DTB crosses a section boundary.
>  	 */
>  	mov	r0, r2, lsr #SECTION_SHIFT
>  	movs	r0, r0, lsl #SECTION_SHIFT
> @@ -229,6 +230,8 @@ __create_page_tables:
>  	add	r3, r3, #PAGE_OFFSET
>  	add	r3, r4, r3, lsr #(SECTION_SHIFT - PMD_ORDER)
>  	orr	r6, r7, r0
> +	str	r6, [r3], #1 << PMD_ORDER
> +	add	r6, r6, #1 << SECTION_SHIFT
>  	str	r6, [r3]
>  
>  #ifdef CONFIG_DEBUG_LL
> 
> 
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-- 
Ben Hutchings
Everything should be made as simple as possible, but not simpler.
                                                           - Albert Einstein

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