linux-kernel - Re: [PATCH 10/28] i386: map enough initial memory to create lowmem mappings

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Date:	Mon, 23 Apr 2007 12:10:42 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Jeremy Fitzhardinge <jeremy@...source.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Chris Wright <chrisw@...s-sol.org>,
	virtualization@...ts.osdl.org, Chuck Ebbert <cebbert@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 10/28] i386: map enough initial memory to create lowmem
 mappings

Eric W. Biederman wrote:
> If (cpu_has_pse) it may only be an additional two pages.
> INIT_MAP_BEYOND is currently mapping a lot more then that.
>   

Ah, yes.  It allocates an extra two pages for pagetables, and then maps
an extra 8MB or so.

>> Would that be necessary?  Is there any need to remap it?  Couldn't you
>> just do the straightforward phys->virt mapping and use the page where it
>> lies?
>>     
>
> Catch-22.  If the page is not mapped yet you can't use it where it lies.

Why not?  Er, except in the case where the page is needed to map itself
- but that can be dealt with with a transient fixmap mapping.

    J
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