Re: [PATCH v2 33/34] ARM: mmu32: Skip reserved ranges during initialization

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 17.05.23 11:03, Sascha Hauer wrote:
> The early MMU code now uses pages to map the OP-TEE area non executable.
> This mapping is overwritten with sections in barebox proper. Refrain
> from doing so by using arch_remap_range() and bypassing reserved areas.
> 
> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> ---
>  arch/arm/cpu/mmu_32.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/cpu/mmu_32.c b/arch/arm/cpu/mmu_32.c
> index 705d27a045..47711bed35 100644
> --- a/arch/arm/cpu/mmu_32.c
> +++ b/arch/arm/cpu/mmu_32.c
> @@ -522,9 +522,17 @@ void __mmu_init(bool mmu_on)
>  	vectors_init();

Took me a while to parse the below code, so I think a comment may be apt:

/*
 * Early mmu init will have mapped everything but the initial memory area
 * (excluding final OPTEE_SIZE bytes) uncached. We have now discovered
 * all memory banks, so let's map all pages, excluding reserved memory areas,
 * cacheable and executable.
 */

>  
>  	for_each_memory_bank(bank) {
> -		create_sections(bank->start, bank->start + bank->size - 1,
> -				PMD_SECT_DEF_CACHED);
> -		__mmu_cache_flush();
> +		struct resource *rsv;
> +		resource_size_t pos;
> +
> +		pos = bank->start;
> +
> +		for_each_reserved_region(bank, rsv) {
> +			arch_remap_range((void *)pos, rsv->start - pos, MAP_CACHED);
> +			pos = rsv->end + 1;
> +		}
> +
> +		arch_remap_range((void *)pos, bank->start + bank->size - pos, MAP_CACHED);

I am a bit bothered by the asymmetry here: Reserved regions in the extra memory banks
will be initially uncached (because outside initmem), so this loop does the correct thing.

For reserved regions within the initial memory, only the OP-TEE region would be uncached,
everything else would just be requested, but is still mapped cacheable.

IMO, that's surprising behavior.

Cheers,
Ahmad

>  	}
>  }
>  

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