linux-kernel - Re: 2.6.25-rc1 xen pvops regression

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Date:	Wed, 20 Feb 2008 13:58:13 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ian Campbell <ijc@...lion.org.uk>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Joel Becker <Joel.Becker@...cle.com>,
	Jody Belka <lists-lkml@...b.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andi Kleen <andi@...stfloor.org>,
	Mika Penttila <mika.penttila@...umbus.fi>
Subject: Re: 2.6.25-rc1 xen pvops regression

Ian Campbell wrote:
> On Tue, 2008-02-19 at 23:43 -0800, H. Peter Anvin wrote:
>   
>> Ian Campbell wrote:
>>     
>>> On Mon, 2008-02-18 at 02:40 -0800, Joel Becker wrote:
>>>       
>>>> On Sun, Feb 17, 2008 at 06:49:21PM +0000, Ian Campbell wrote:
>>>>         
>>>>> x86/xen: Do not scan for DMI unless the DMI region is reserved by e820.
>>>>>           
>>>> 	This fixed it.  I'm now booting successfully.  Thank you!
>>>>         
>>> Excellent. Jeremy, are you happy for this to go in?
>>>       

I had no problem with it, but Peter's objection seems substantial enough.

> As far as the actual change goes I was assuming that any machine that
> has DMI/SMBIOS would easily be new enough to have an E820 which could be
> expected to reserve this region. Looks like I was mistaken about how
> long E820 had been around and/or how reliably it is used to reserve the
> tables.
>
> Anyway, will have to think of another solution.
>   

Well, the way we've handled this kind of thing elsewhere is to just 
reserve that pseudophys address space in earlish Xen init code and fill 
it with not-DMI things (zero, I guess).  It's a bit of a waste of 
memory, but maybe we can recover it once DMI has given up and gone 
away.  This also makes it easy to insert faked-up DMI info if that turns 
out to be useful.


    J
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