linux-kernel - Re: [PATCH] i386: For debugging, make the initial page table setup less forgiving.

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Message-ID: <m1ejm8s489.fsf@ebiederm.dsl.xmission.com>
Date:	Wed, 25 Apr 2007 12:23:18 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>, Andi Kleen <ak@...e.de>,
	Zachary Amsden <zach@...are.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i386: For debugging, make the initial page table setup less forgiving.

"H. Peter Anvin" <hpa@...or.com> writes:

> Eric W. Biederman wrote:
>>> This patch only affects the initial page tables, which should have been
>>> thrown out *way* long ago at this point.
>> 
>> Yes.  I noticed this was happening a few days ago.
>> I must not have mentioned it loudly enough.
>
> You mentioned the continued use of init_mm.  This is *very* different.
>
> What we're seeing here is that ON PSE-CAPABLE HARDWARE, we continue to
> not just use the init_mm page directory, but the actual page *tables*,
> which should all have been replaced with PSE large pages to begin with.

That is what I meant if not what I communicated.  If you read the code that
is exactly what it is trying to do.

> Reusing the initial page tables on non-PSE-capable hardware *sort of*
> makes sense, but his hardware should not fall in that category, I don't
> think?  (Unless it's one of these machines that fall over if you map the
> bottom 4 MB with PSE pages?)

I agree that I don't think the current behaviour makes sense.  I think
the code has accumulated so many small modifications that is very far
from making sense in the corner cases.

arch/i386 either needs to be frozen as a legacy only thing or
it needs to be cleaned up so we can continue to enhance the code.

Eric
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