linux-kernel - Re: [Bug Fix]: Do 32-bit table calculations in pre-processor

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Date:	Fri, 3 Jul 2009 15:45:42 -0500
From:	"Michael S. Zick" <lkml@...ethan.org>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [Bug Fix]: Do 32-bit table calculations in pre-processor

On Fri July 3 2009, Yinghai Lu wrote:
> On Fri, Jul 3, 2009 at 11:14 AM, Michael S. Zick<lkml@...ethan.org> wrote:
> > Here is one I have found useful in my VIA processor bug hunting:
> >
> > diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
> > index 3068388..2303d86 100644
> > --- a/arch/x86/kernel/head_32.S
> > +++ b/arch/x86/kernel/head_32.S
> > @@ -61,7 +61,7 @@
> >
> >  /* Enough space to fit pagetables for the low memory linear map */
> >  MAPPING_BEYOND_END = \
> > -       PAGE_TABLE_SIZE(((1<<32) - __PAGE_OFFSET) >> PAGE_SHIFT) << PAGE_SHIFT
> > +       PAGE_TABLE_SIZE((1<<20) - (__PAGE_OFFSET >> PAGE_SHIFT)) << PAGE_SHIFT
> >
> >  /*
> >  * Worst-case size of the kernel mapping we need to make:
> >
> > = = =
> >
> > Before:
> >
> >  #5 [0000010000 - 0000011000]          PGTABLE ==> [0000010000 - 0000011000]
> >  #6 [0000011000 - 0000015000]          BOOTMAP ==> [0000011000 - 0000015000]
> >
> > After:
> >
> >  #5 [0000010000 - 000007d000]          PGTABLE ==> [0000010000 - 000007d000]
> >  #6 [000007d000 - 0000081000]          BOOTMAP ==> [000007d000 - 0000081000]
> >
> 
> that PGTABLE is from early resource. and it is filled by init_memory_mapping()
> 
> it mean preallocated pgtable to MAPPING_BEYOND_END is small now after
> patch. and init_memory_mapping try to get more.
>

Ah, so - the labels are a bit misleading - but that makes since.
 
> please send out whole dmesg. with and without your patch. it could
>

Am having technical problems at the moment - maybe later today I
can get you the information you need.

> print out initial mapped before e820 allocation is involved for 32bit
>         printk(KERN_DEBUG "initial memory mapped : 0 - %08lx\n",
>                         max_pfn_mapped<<PAGE_SHIFT);
> 
>
> 
> your patch should be right. except to change that 12 to PAGE_SHIFT
> 

Not all pages are 4K, but as you point out, that can be fixed.

> YH
> 
> 

Mike
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