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

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Message-ID: <479912B0.2080506@goop.org>
Date:	Thu, 24 Jan 2008 14:35:28 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	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.

H. Peter Anvin wrote:
> In other words, reusing the early page tables isn't all that 
> straightforward.  It may easily be that it's better to build a new set 
> of page tables from scratch, however, it would *still* be beneficial 
> to have the early page tables be in the same format as the later one, 
> since it lets us use the fixmap area, and therefore 
> {bt,early}_ioremap() much sooner.

Yes, and it simplifies Xen as it always starts guest domains in the 
appropriate pagetable mode and doesn't let the guest change it on the 
fly.  If early_ioremap depends on non-PAE early pagetables in an 
otherwise PAE kernel, we'd need to go to some effort to make sure all 
the early_ioremap stuff is skipped (which would be possible but 
unpleasant for domU, but very bad in dom0).

    J

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