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

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Date:	Wed, 25 Apr 2007 11:18:12 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, 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.

Eric W. Biederman wrote:
> "H. Peter Anvin" <hpa@...or.com> writes:
>
>   
>> 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.
>>     
>
> Yes.  I noticed this was happening a few days ago.
> I must not have mentioned it loudly enough.
>   

I might have introduced it as part of the paravirt_ops patches.  When
setting up pagetables under Xen, we need to make sure we preserve the
initial mappings Xen put in place (it starts the VM with paging enabled,
and a sane initial pagetable).  This may have leaked over into native if
it doesn't replace an existing entry.

Hm, but it should be overwriting small mappings with large ones.  Maybe
I overlooked that.

> I'm halfway through putting together a patchset to address a
> bunch of these.
>
> I haven't yet resolved how I want to allocate the pages for the
> identity mapping of the page table yet.  I can't use the bootmem
> allocate as it exists because that assumes the page is mapped
> into the address space already.
>   

Are you going to clash horribly with the paravirt pagetable setup?  We
should probably coordinate if so.

    J
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