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

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Message-ID: <47991A6C.8060007@zytor.com>
Date:	Thu, 24 Jan 2008 15:08:28 -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:
>> 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. 
> 
> Right.
> 
> Xen provides a initial set of pagetables in the appropriate format, so 
> what head.S generates is moot.  For simplicity I graft the Xen-provided 
> pagetables into swapper_pg_dir in xen_start_kernel, so it is the 
> functional equivalent to the head.S pagetable construction.
> 
> We also don't (yet) support PSE, so that's a non-issue for us too.
> 

While we're mucking around in this area, there is another thing which we 
should eventually get around to fixing:

we need a set of page tables with an identity mapping as well as the 
kernel mapping, for trampolining (during startup, but also during things 
like ACPI suspend/resume.)  Right now, we let those be the swapper page 
tables, but that's probably not really a good idea, since it can hide bugs.

	-hpa
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