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From"Michael S. Zick" <>
Subject[Bug Fix]: Do 32-bit table calculations in pre-processor
DateFri, 3 Jul 2009 13:14:30 -0500
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]
Someone who knows mm check which is the reasonable value please.

Mike


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