linux-kernel - Re: [PATCH] x86: simplify HIGHMEM-related Kconfig entries

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Message-ID: <496F6DFC.90006@zytor.com>
Date:	Thu, 15 Jan 2009 09:10:20 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jan Beulich <jbeulich@...ell.com>, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: simplify HIGHMEM-related Kconfig entries

Ingo Molnar wrote:
>>>
>>> 	No highmem	- No highmem, no PAE
>>> 	HIGHMEM4G	- Highmem, no PAE
>>> 	HIGHMEM64G	- Highmem, PAE
>>>
>>> So X86_PAE and HIGHMEM4G is a bit of a contradiction.  I haven't looked 
>>> at the logic in detail, or remember offhand if there have been any 
>>> weakening of the definitions above; e.g. someone could have implemented 
>>> a way to do PAE without highmem, to get access to the NX bits.
>> Exactly - .23 made PAE an independently selectable option (in 
>> particular, the no-highmem+PAE combination is now valid), but I can't 
>> see why it added the !HIGHMEM4G dependency.
> 
> There's no deep reason, it just has never really been tested that way. I 
> think we should try it.

If so, what would be the difference between HIGHMEM4G and HIGHMEM64G in
that case at all?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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