linux-kernel - Re: pud_bad vs pud

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Date:	Thu, 05 Feb 2009 13:05:36 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Hugh Dickins <hugh@...itas.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	William Lee Irwin III <wli@...ementarian.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: pud_bad vs pud_bad

Hugh Dickins wrote:
>> Hardware doesn't allow it.  It will explode (well, trap) if you set anything
>> other than P in the top level.
>>     
>
> Oh, interesting, I'd never realized that.
>   

There are some later extensions to reuse some of the bits for things 
like tlb reload policy (I think; I'd have to check to be sure), so 
they're fairly non-pte-like.

>> By the by, what are the chances we'll be able to deprecate non-PAE 32-bit?
>>     
>
> I sincerely hope 0!  I shed no tears at losing support for NUMAQ,
> but why should we be forced to double all the 32-bit ptes?  You want
> us all to be using NX?  Or you just want to cut your test/edit matrix -
> that I can well understand!
>   

Yes, that's the gist of it.  We could simplify things by having only one 
pte format and only have to parameterise with 3/4 level pagetables.  
We'd lose support for non-PAE cpus, including the first Pentium M (which 
is probably still in fairly wide use, unfortunately).

    J
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