linux-kernel - Re: pud_bad vs pud

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Message-ID: <Pine.LNX.4.64.0902052046240.18431@blonde.anvils>
Date:	Thu, 5 Feb 2009 20:51:40 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
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

On Thu, 5 Feb 2009, Jeremy Fitzhardinge wrote:
> Hugh Dickins wrote:
> > However... I forget how the folding works out.  The pgd in the 32-bit
> > PAE case used to have just the pfn and the present bit set in that
> > little array of four entries: if pud_bad() ends up getting applied
> > to that, I guess it will blow up.
> 
> Ah, that's a good point.
> 
> > If so, my preferred answer would actually be to make those 4 entries
> > look more like real ptes; but you may think I'm being a bit silly.
> 
> 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.

> 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!

Hugh
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