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

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Date:	Thu, 19 Apr 2007 16:47:56 -0400
From:	Chuck Ebbert <cebbert@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...ux-foundation.org>,
	virtualization@...ts.osdl.org, lkml <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Zachary Amsden <zach@...are.com>,
	Chris Wright <chrisw@...s-sol.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 10/28] i386: map enough initial memory to create lowmem
 mappings

Jeremy Fitzhardinge wrote:
> head.S creates the very initial pagetable for the kernel.  This just
> maps enough space for the kernel itself, and an allocation bitmap.
> The amount of mapped memory is rounded up to 4Mbytes, and so this
> typically ends up mapping 8Mbytes of memory.
> 
> When booting, pagetable_init() needs to create mappings for all
> lowmem, and the pagetables for these mappings are allocated from the
> free pages around the kernel in low memory.  If the number of
> pagetable pages + kernel size exceeds head.S's initial mapping, it
> will end up faulting on an unmapped page.  This will only happen with
> specific combinations of kernel size and memory size.
> 
> This patch makes sure that head.S also maps enough space to fit the
> kernel pagetables as well as the kernel itself.  It ends up using an
> additional two pages of unreclaimable memory.
> 
> Signed-off-by: Jeremy Fitzhardinge <jeremy@...source.com>
> Acked-by: "H. Peter Anvin" <hpa@...or.com>
> Cc: Andi Kleen <ak@...e.de>
> Cc: Zachary Amsden <zach@...are.com>
> Cc: Chris Wright <chrisw@...s-sol.org>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>,

Is some version of this going in for 2.6.21, or is it not a real problem?
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