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

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Date:	Fri, 3 Jul 2009 13:07:04 -0700
From:	Yinghai Lu <yhlu.kernel@...il.com>
To:	lkml@...ethan.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [Bug Fix]: Do 32-bit table calculations in pre-processor

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.

please send out whole dmesg. with and without your patch. it could
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

YH
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