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

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Message-ID: <86802c440907031308j3f996db6g9dfb1b8f9ccb7e7f@mail.gmail.com>
Date:	Fri, 3 Jul 2009 13:08:49 -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 1:07 PM, Yinghai Lu<yhlu.kernel@...il.com> 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.
>
> 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
>
mean

>>  /* 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<<(32 - PAGE_SHIFT)) - (__PAGE_OFFSET >> PAGE_SHIFT)) << PAGE_SHIFT

YH
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