linux-kernel - Re: [PATCH] x86: Construct 32 bit boot time page tables in native format.

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Message-ID: <20080125074910.GD4134@ucw.cz>
Date:	Fri, 25 Jan 2008 07:49:10 +0000
From:	Pavel Machek <pavel@....cz>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Ian Campbell <ijc@...lion.org.uk>, Ingo Molnar <mingo@...e.hu>,
	Mika Penttilä <mika.penttila@...umbus.fi>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] x86: Construct 32 bit boot time page tables in native format.

On Thu 2008-01-24 16:27:58, H. Peter Anvin wrote:
> Pavel Machek wrote:
> >>>
> >>I just looked at the ACPI suspend code, and it looks 
> >>like it hacks its own identity map at runtime.  Pavel, 
> >>am I reading that code right?
> >
> >Yes, I think so, I believe we do it on both 32 and 64 
> >bit now.
> >
> 
> So the background to this... we need an identity map to 
> trampoline at early boot, obviously, but we'd like it to 
> not stick around more than necessary.  We have 
> zap_low_mappings() now but it's not really sufficient.
> 
> Secondary SMP processors need these mappings during 
> trampolining -- presumably including CPU hotplug -- and 
> I'm suspecting it might simply make sense to use a 
> separate set of page tables (with both the identity and 
> the kernel map) for trampolining and just keep them 
> around.  That way they would be usable for ACPI as well.

That would enable some cleanups, yes.
						Pavel
-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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