linux-kernel - Re: [PATCH -mm 1/3] i386 boot: replace boot_ioremap with enhanced bt_ioremap

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Date:	Fri, 18 Jan 2008 09:54:08 -0500
From:	"H. Peter Anvin" <hpa@...or.com>
To:	huang ying <huang.ying.caritas@...il.com>
CC:	Ian Campbell <ijc@...lion.org.uk>,
	"Huang, Ying" <ying.huang@...el.com>, akpm@...ux-foundation.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org, Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH -mm 1/3] i386 boot: replace boot_ioremap with enhanced
 bt_ioremap - enhance bt_ioremap

huang ying wrote:
> 
> If CONFIG_X86_PAE is defined, the set_pte, clear_pte etc will operate
> 3-level page tables, while on i386, the early page table is always
> 2-level, so set_pte, clear_pte etc functions can not be used here. The
> boot_ioremap use a trick to deal with this problem. The CONFIG_X86_PAE
> is undefined in arch/x86/mm/boot_ioremap_32.c unconditionally, so the
> 2-level page table handling function is always used.
> 
> Is the method used by boot_ioremap better for Xen?
> 

Eric Biederman had a patchset that makes a PAE kernel use PAE page 
tables from the start.  That is really The Right Thing[TM].

	-hpa
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