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 15:54:25 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	huang ying <huang.ying.caritas@...il.com>,
	"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


On Fri, 2008-01-18 at 09:54 -0500, H. Peter Anvin wrote:
> 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].

That's much saner than dup'ing up the early ioremap stuff to support
both PAE and non-PAE at runtime, which is about the only idea I've got
for fixing this right now...

I think I'll just back out the early_ioremap patches locally for now and
wait for Eric's patches which should cause the fix for this issue to
just fall out in the wash.

Ian.
-- 
Ian Campbell
Current Noise: Mistress - Mistress

Everything should be built top-down, except this time.

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