linux-kernel - Re: [PATCH] i386: For debugging, make the initial page table setup less forgiving.

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Date:	Wed, 25 Apr 2007 08:28:32 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>, Andi Kleen <ak@...e.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Zachary Amsden <zach@...are.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i386: For debugging, make the initial page table setup
 less forgiving.

Andrew Morton wrote:

> 
> This patch causes oopses after a minute or so running LTP's
> 
> ./testcases/bin/growfiles -W gf16 -b -e 1 -i 0 -L 120 -u -g 4090 -T 100 -t 408990 -l -C 10 -c 1000 -S 10 -f Lgf02_
> 
> on everyone's favoutite Vaio, configured with
> http://userweb.kernel.org/~akpm/config-sony.txt
> 

*BLINK*

This patch only affects the initial page tables, which should have been
thrown out *way* long ago at this point.

Yet they seem to have stuck around.  This is a very bad thing on many
levels, especially since we should have switched the kernel 1:1 area
over to PSE pages a long time ago.

> BUG: unable to handle kernel paging request at virtual address c084fa8c
>  printing eip:
> c0174c46
> *pde = 0042a027
> *pte = 00000000

Touching a non-PSE page which is zero, and quite consistent with being a
remnant from the original page tables.

Methinks this has smoked out a bug in the initial page table setup which
probably has been a performance roadblock for quite some time.

	-hpa
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