Messages in this thread | | | From | "Michael S. Zick" <> | Subject | Re: [Bug Fix]: Do 32-bit table calculations in pre-processor | Date | Fri, 3 Jul 2009 14:03:17 -0500 |
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On Fri July 3 2009, Jeremy Fitzhardinge wrote: > [ Missed some recipients. ] > > On 07/03/09 11:14, Michael S. Zick 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 > > > > > > These calculations are performed by the assembler, not the > preprocessor. I think this transformation looks correct (in that its an > identity with the original), but my understanding is that the assembler > does it calculations in arbitrary precision, so there's no need to worry > about limiting the arithmetic to 32-bits. > > > /* > > * 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] > > > > Someone who knows mm check which is the reasonable value please. > > > > > The PGTABLE reservation seems much too big. I think 1 page should be > sufficient for a system with large pages. Even if not, 0x6d000 is way > too large. And they symptoms of failing to reserve the initial > pagetable are pretty non-subtle. >
Random system halts, deadlocks with interrupts disabled? Yup, that sounds familiar.
If I ever get more than a stopped machine with a glowing power light; I will be certain to share.
Mike > J > >
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