Re: [PATCH v2 2/2] ARM: mmu_32: fix setting up zero page when it is in SDRAM

[Sascha Hauer <s.hauer@pengutronix.de>]

On Wed, May 31, 2023 at 01:58:33PM +0200, Ahmad Fatoum wrote:
> > From b6e5c92682467496bd9c57918996f1feffda2dd6 Mon Sep 17 00:00:00 2001
> > From: Sascha Hauer <s.hauer@pengutronix.de>
> > Date: Wed, 31 May 2023 11:58:51 +0200
> > Subject: [PATCH] ARM: mmu_32: fix setting up zero page when it is in SDRAM
> > 
> > We used to skip setting the zero page to faulting when SDRAM starts at
> > 0x0. As bootm code now explicitly sets the zero page accessible before
> > copying ATAGs there this should no longer be necessary, so
> > unconditionally set the zero page to faulting during MMU startup.  This
> > also moves the zero page and vector table setup after the point the
> > SDRAM has been mapped cachable, because otherwise the zero page and
> > possibly the vector table mapping would be overwritten.
> > 
> > Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> > ---
> >  arch/arm/cpu/mmu_32.c | 23 +++++++++--------------
> >  1 file changed, 9 insertions(+), 14 deletions(-)
> > 
> > diff --git a/arch/arm/cpu/mmu_32.c b/arch/arm/cpu/mmu_32.c
> > index c4e5a3bb0a..14775768a3 100644
> > --- a/arch/arm/cpu/mmu_32.c
> > +++ b/arch/arm/cpu/mmu_32.c
> > @@ -461,19 +461,14 @@ static int set_vector_table(unsigned long adr)
> >  
> >  static void create_zero_page(void)
> 
> Is this commit incomplete? Vectors should be set up unconditionally and
> create_zero_page should be called after it.

Vectors are set up unconditionally and create_zero_page() is called the
same way as before.

Sascha

> 
> >  {
> > -	struct resource *zero_sdram;
> > +	/*
> > +	 * In case the zero page is in SDRAM request it to prevent others
> > +	 * from using it
> > +	 */
> > +	request_sdram_region("zero page", 0x0, PAGE_SIZE);
> >  
> > -	zero_sdram = request_sdram_region("zero page", 0x0, PAGE_SIZE);
> > -	if (zero_sdram) {
> > -		/*
> > -		 * Here we would need to set the second level page table
> > -		 * entry to faulting. This is not yet implemented.
> > -		 */
> > -		pr_debug("zero page is in SDRAM area, currently not supported\n");
> > -	} else {
> > -		zero_page_faulting();
> > -		pr_debug("Created zero page\n");
> > -	}
> > +	zero_page_faulting();
> > +	pr_debug("Created zero page\n");
> >  }
> >  
> >  /*
> > @@ -530,8 +525,6 @@ void __mmu_init(bool mmu_on)
> >  
> >  	pr_debug("ttb: 0x%p\n", ttb);
> >  
> > -	vectors_init();
> > -
> >  	/*
> >  	 * Early mmu init will have mapped everything but the initial memory area
> >  	 * (excluding final OPTEE_SIZE bytes) uncached. We have now discovered
> > @@ -552,6 +545,8 @@ void __mmu_init(bool mmu_on)
> >  
> >  		remap_range((void *)pos, bank->start + bank->size - pos, MAP_CACHED);
> >  	}
> > +
> > +	vectors_init();
> >  }
> >  
> >  /*
> 
> -- 
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> 

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