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List:       linux-arm-kernel
Subject:    Re: On TLB flushing
From:       Marc Singer <elf () buici ! com>
Date:       2004-04-16 18:17:30
Message-ID: 20040416181730.GB18700 () flea
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On Fri, Apr 16, 2004 at 07:04:23PM +0100, Russell King - ARM Linux wrote:
> > The call ptep_to_address () looks into the node data and composes an
> > address.  
> > 
> >     unmap: breakin ptep c0341820 address 00104000
> >     kmap_atomic_to_page c0235228
> >     low_bits 00104000
> >     page->index 00000000
> > 
> > The address value needs to be 0x00008000 for a correct cache and TLB
> > flush.  I know this is a big question: how is this supposed to work?
> 
> The answer is it obviously doesn't; the calculation of low_bits is
> most definitely wrong - PTRS_PER_PTE is not the right definition to
> describe the ratio of bytes in a page to PTE entries.
> 
> Working from your data above, this means ptep was 0x820.  Using the

  ptep is 0xc0341820, it says so in the first line. 

> new calculation below, PTRS_PER_PTE is 512, and sizeof(pte_t) is 4.
> This gives (0x820 & 0x7ff) * 0x400 which gives: 0x8000 - the right
> answer!

That's part of the answer.  Is it guaranteed that the node_map's
page->index is the correct upper portion of the virtual address?

> This bug will affect _all_ ARM platforms, so it should be reproducable
> here...

Hmm.

> 
> Could you try this patch?

Do we need an arm (arm32) specific version?

> 
> Index: pgcl-2.6.5-mm6/include/asm-generic/rmap.h
> ===================================================================
> --- pgcl-2.6.5-mm6.orig/include/asm-generic/rmap.h	2004-04-03 19:37:24.000000000 -0800
> +++ pgcl-2.6.5-mm6/include/asm-generic/rmap.h	2004-04-16 10:57:07.000000000 -0700
> @@ -57,7 +57,8 @@
>  {
>  	struct page * page = kmap_atomic_to_page(ptep);
>  	unsigned long low_bits;
> -	low_bits = ((unsigned long)ptep & ~PAGE_MASK) * PTRS_PER_PTE;
> +	low_bits = ((unsigned long)ptep & (PTRS_PER_PTE*sizeof(pte_t) - 1))
> +			* (PAGE_SIZE/sizeof(pte_t));
>  	return page->index + low_bits;
>  }
>  

Bless my soul.

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