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

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

On 31.05.23 14:38, Sascha Hauer wrote:
> 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.

So zero page is requested first and then on platforms with vector at
address 0 requesting fails and we are left without configured IVT?

> 
> 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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