Message-ID: <4790BD90.9060303@zytor.com>
Date: Fri, 18 Jan 2008 09:54:08 -0500
From: "H. Peter Anvin" <hpa@zytor.com>
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To: huang ying <huang.ying.caritas@gmail.com>
CC: Ian Campbell <ijc@hellion.org.uk>, "Huang, Ying" <ying.huang@intel.com>,
       akpm@linux-foundation.org, Thomas Gleixner <tglx@linutronix.de>,
       Ingo Molnar <mingo@redhat.com>, Andi Kleen <ak@suse.de>,
       linux-kernel@vger.kernel.org, Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH -mm 1/3] i386 boot: replace boot_ioremap with enhanced
 bt_ioremap - enhance bt_ioremap
References: <1200375906.3505.30.camel@caritas-dev.intel.com>	 <1200646105.17230.28.camel@cthulhu.hellion.org.uk> <851fc09e0801180654u6957f966g47c7629db6d4b2b0@mail.gmail.com>
In-Reply-To: <851fc09e0801180654u6957f966g47c7629db6d4b2b0@mail.gmail.com>
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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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