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

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Date:	Fri, 16 Jan 2009 11:57:07 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Ingo Molnar" <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>
Cc:	<tglx@...utronix.de>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: simplify HIGHMEM-related Kconfig entries

>>> "H. Peter Anvin" <hpa@...or.com> 15.01.09 18:10 >>>
>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?

For example being able to select the DMADEVICES config option.

Jan

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