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

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Message-ID: <47992D0E.2070700@zytor.com>
Date:	Thu, 24 Jan 2008 16:27:58 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Pavel Machek <pavel@....cz>
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.

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.

> (It is early here. And I almost got the .c wakeup code to work... it
> already sets the mode).

Sweet!

	-hpa
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