linux-kernel - Re: [Lguest] lguest: unhandled trap

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Message-Id: <1224494055.9053.192.camel@zakaz.uk.xensource.com>
Date:	Mon, 20 Oct 2008 10:14:15 +0100
From:	Ian Campbell <Ian.Campbell@...citrix.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	maluta_tiago@...oo.com.br, lguest@...abs.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [Lguest] lguest: unhandled trap

On Mon, 2008-10-20 at 09:53 +0200, Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> 
> > Ingo Molnar wrote:
> >> i think Xen can withstand DMI scanning just fine.
> >>
> >> without having seen any background, my general feeling is that lguest 
> >> should either do what Xen does and reserve the classic BIOS ranges 
> >> that we probe - or we should make DMI scanning more robust by making 
> >> sure real RAM ranges are never probed. (only ranges that the BIOS 
> >> itself marks as reserved in the e820 map)
> >
> > We considered doing that, but decided that there was so many other 
> > pieces of code around the place that assume that the ISA area is 
> > special, that just reserving it was the best course of action.
> 
> yeah - for _any_ virtual machine environment it's beneficial to look as 
> much like a normal PC as possible, because normal PCs is where the code 
> gets tested most.
> 
> Nevertheless if this is the only current roadblock for lguest then i 
> wouldnt find it objectionable to make DMI scanning more robust that way 
> - the two are complimentary. [ With an initial transitionary period of 
> generating printks and WARN()s when we try to scan general RAM areas. ]

Wasn't there some concern about BIOSes which don't correctly reserve
their DMI tables? Or don't even have e820 maps? H. Peter once said:

> It's pretty standard for 0xf0000...0x100000 to be marked RESERVED in
> E820 on real hardware (including the system I'm typing on right now.)
> It is so marked to indicate that hardware cannot be mapped into that
> space.  However, you can't rely on this fact -- heck, you can't rely on
> E820 even existing on a real machine.  I have specimens of real-life
> machines that go both ways.

Ian.


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