linux-kernel - Re: divorce CONFIG_X86_PAE from CONFIG

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Message-ID: <Pine.LNX.4.58.0706130809240.2702@be1.lrz>
Date:	Wed, 13 Jun 2007 09:26:30 +0200 (CEST)
From:	Bodo Eggert <7eggert@....de>
To:	William Lee Irwin III <wli@...omorphy.com>
cc:	linux-kernel@...r.kernel.org, Adrian Bunk <bunk@...sta.de>
Subject: Re: divorce CONFIG_X86_PAE from CONFIG_HIGHMEM64G

Since your (William) patch will change the kconfig files my proposed patch
would change, could you please add those changes? 

I hand-updated the patch below as recommended by the original discussion 
on LKML. It won't aply as-is because of that (and because of your changes).


--- 2.6.21/arch/i386/Kconfig.ori	2007-06-06 13:41:09.000000000 +0200
+++ 2.6.21/arch/i386/Kconfig	2007-06-06 14:07:40.000000000 +0200
@@ -495,8 +495,8 @@ config NOHIGHMEM
 	bool "off"
 	depends on !X86_NUMAQ
 	---help---
-	  Linux can use up to 64 Gigabytes of physical memory on x86 systems.
-	  However, the address space of 32-bit x86 processors is only 4
+	  Linux can use up to 64 Gigabytes of physical address space on x86
+	  systems. However, the address space of 32-bit x86 processors is only 4
 	  Gigabytes large. That means that, if you have a large amount of
 	  physical memory, not all of it can be "permanently mapped" by the
 	  kernel. The physical memory that's not permanently mapped is called
@@ -510,8 +510,15 @@ config NOHIGHMEM
 	  by the kernel to permanently map as much physical memory as
 	  possible.
 
-	  If the machine has between 1 and 4 Gigabytes physical RAM, then
+
+	  If the machine has between 1 and about 3 Gigabytes physical RAM, 
+         then
 	  answer "4GB" here.
+	  
+	  The PCI address space will usually take 512 MB or 1 GB of address
+	  space. This address space is unavailable to RAM, but depending on the
+	  chipset (and BIOS settings), memory overlapping the PCI address space
+	  may be mapped beyond the 4 GB limit and be available using "64GB".
+
 
 	  If more than 4 Gigabytes is used then answer "64GB" here. This
 	  selection turns Intel PAE (Physical Address Extension) mode on.
@@ -520,6 +527,10 @@ config NOHIGHMEM
 	  processors (Pentium Pro and better). NOTE: If you say "64GB" here,
 	  then the kernel will not boot on CPUs that don't support PAE!
 
+	  An additional benefit of the 64GB-Mode is the availability of the
+	  no-execute-pageflag, which can be used to prevent some attacks from
+	  injecting malicious code into applications.
+
 	  The actual amount of total physical memory will either be
 	  auto detected or can be forced by using a kernel command line option
 	  such as "mem=256M". (Try "man bootparam" or see the documentation of
@@ -532,14 +543,14 @@ config HIGHMEM4G
 	bool "4GB"
 	depends on !X86_NUMAQ
 	help
-	  Select this if you have a 32-bit processor and between 1 and 4
+	  Select this if you have a 32-bit processor and between 1 and 3
 	  gigabytes of physical RAM.
 
 config HIGHMEM64G
-	bool "64GB"
+	bool "64GB (enables no-execute memory protection if available)"
 	depends on X86_CMPXCHG64
 	help
-	  Select this if you have a 32-bit processor and more than 4
+	  Select this if you have a 32-bit processor and more than 3
 	  gigabytes of physical RAM.
 
 endchoice
-- 
RAM DISK is not an installation procedure! 
-
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