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

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Message-Id: <200907031314.36243.lkml@morethan.org>
Date:	Fri, 3 Jul 2009 13:14:30 -0500
From:	"Michael S. Zick" <lkml@...ethan.org>
To:	linux-kernel@...r.kernel.org
Subject: [Bug Fix]: Do 32-bit table calculations in pre-processor

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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