Re: [PATCH v2 08/10] ARM: mmu: use reserve mem entries to modify maps

[Sascha Hauer <sha@pengutronix.de>]

On Mon, Sep 12, 2022 at 05:15:45PM +0200, Ahmad Fatoum wrote:
> Hi,
> 
> On 12.09.22 14:01, Sascha Hauer wrote:
> > This patch breaks NAND support on my Phytec i.MX6 board. There are some
> > problems with this patch, so I ended up reverting it for now.
> 
> I wonder why. I see no memory reserves in imx6q-phytec-phycore-som-nand.dts
> and the files it includes.
> 
> > 
> > On Wed, Aug 17, 2022 at 01:42:42PM +0200, Ahmad Fatoum wrote:
> >> @@ -468,11 +469,28 @@ void __mmu_init(bool mmu_on)
> >>  	vectors_init();
> >>  
> >>  	for_each_memory_bank(bank) {
> >> +		struct resource *rsv;
> >> +
> >>  		create_sections(ttb, bank->start, bank->start + bank->size - 1,
> >>  				PMD_SECT_DEF_CACHED);
> >> -		__mmu_cache_flush();
> >> +
> >> +		for_each_reserved_region(bank, rsv) {
> >> +			create_sections(ttb, resource_first_page(rsv),
> >> +					resource_count_pages(rsv),
> >> +					attrs_uncached_mem());
> >> +		}
> > 
> > This operates on 1MiB sections, so everything requiring a finer
> > granularity will fail here. Not sure if we currently need that, but not
> > even issuing a warning is not good.
> 
> At worst it'd needlessly mark some memory uncached/XN. If users are
> affected, they will notice and we can revisit this. I could add a debug
> print here.
> 
> I need to rework this though, because I see now create_sections differs
> between ARM64 and ARM32. On ARM64, it accepts the last address as argument,
> while on ARM64, it's the size.. resource_count_pages() is not a nice
> name either, because it returns bytes (aligned up to PAGE_SIZE).
> 
> > 
> >>  	}
> >>  
> >> +	/*
> >> +	 * We could set_ttbr(ttb) here instead and save on the copy, but
> >> +	 * for now we play it safe, so we don't mess with the older ARMs.
> >> +	 */
> >> +	if (oldttb) {
> >> +		memcpy(oldttb, ttb, ARM_TTB_SIZE);
> >> +		free(ttb);
> >> +	}
> > 
> > in the early MMU case the MMU still uses 'oldttb' as ttb whereas 'ttb'
> > now points to invalid memory. Still functions like arm_create_pte()
> > still operate on 'ttb'. It looks like a ttb = oldttb is missing here.
> 
> Why would ttb point at invalid memory? It's allocated unconditionally
> with xmemalign and freed here.

It becomes clearer when you look at the scope of the variable.

> 
> > Also I wonder when we have to map the reserved regions as execute never,
> > then the early MMU setup seems broken as well, as that creates a flat
> > mapping without honoring the reserved regions. Shouldn't that be fixed?
> 
> Yes, see excerpt from cover letter:
> 
> "Note that this doesn't yet solve all problems. For example, PPA secure
>  monitor installation on Layerscape may happen with CONFIG_MMU_EARLY=y,
>  in which case barebox in EL2 may speculate into the secure memory
>  before any device tree reserved-memory settings are considered. For this
>  reason, both early MMU and normal MMU setup must be aware of the
>  reserved memory regions. The original patch set by Rouven used FDT
>  parsing in PBL to achieve this, but this is omitted here to limit
>  scope of the patch series. Instead we only handle the CONFIG_OPTEE_SIZE
>  case out-of-the-box."

Ok.

Sascha

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