Re: [PATCH 07/12] i386: Add missing !X86_PAE dependincy to the 2G/2G split.

From: Eric W. Biederman
Date: Mon Apr 30 2007 - 12:41:02 EST

"H. Peter Anvin" <hpa@xxxxxxxxx> writes:

> Eric W. Biederman wrote:
>> When in PAE mode we require that the user kernel divide to be
>> on a 1G boundary. The 2G/2G split does not have that property
>> so require !X86_PAE
> ?????
> -hpa

>From arch/i386/Kconfig:
> choice
> depends on EXPERIMENTAL
> prompt "Memory split" if EMBEDDED
> default VMSPLIT_3G
> help
> Select the desired split between kernel and user memory.
> If the address range available to the kernel is less than the
> physical memory installed, the remaining memory will be available
> as "high memory". Accessing high memory is a little more costly
> than low memory, as it needs to be mapped into the kernel first.
> Note that increasing the kernel address space limits the range
> available to user programs, making the address space there
> tighter. Selecting anything other than the default 3G/1G split
> will also likely make your kernel incompatible with binary-only
> kernel modules.
> If you are not absolutely sure what you are doing, leave this
> option alone!
> config VMSPLIT_3G
> bool "3G/1G user/kernel split"
> config VMSPLIT_3G_OPT
> depends on !HIGHMEM
> bool "3G/1G user/kernel split (for full 1G low memory)"
> config VMSPLIT_2G
> depends on !X86_PAE
> bool "2G/2G user/kernel split"
> config VMSPLIT_1G
> bool "1G/3G user/kernel split"
> endchoice
> config PAGE_OFFSET
> hex
> default 0xB0000000 if VMSPLIT_3G_OPT
> default 0x78000000 if VMSPLIT_2G
> default 0x40000000 if VMSPLIT_1G
> default 0xC0000000

The default PAGE_OFFSET is at 0x7800000 for the 2G/2G split.
All of these options were originally !X86_PAE, I assume
the intention was to be able to have 2G of RAM without
needing high memory.

I don't really care I just saw the problem and decided to prevent
people trying a combination that simply doesn't work.

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