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

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Message-ID: <479913BA.8000506@zytor.com>
Date:	Thu, 24 Jan 2008 14:39:54 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
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.

Jeremy Fitzhardinge wrote:
> 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).
> 

Yeah, and it's ugly for the kernel proper, so that bit is a no-brainer. 
  It's just a matter of hammering out the details.

It doesn't sound from the above that you have any opinion either way 
about reusing the initial page tables or creating a new set, as long as 
they're in the same format.

	-hpa
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