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    SubjectRe: [Bug Fix]: Do 32-bit table calculations in pre-processor
    Date
    On Fri July 3 2009, Yinghai Lu wrote:
    > On Fri, Jul 3, 2009 at 11:14 AM, Michael S. Zick<lkml@morethan.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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