Re: [Lguest] lguest: unhandled trap

From: Ian Campbell
Date: Mon Oct 20 2008 - 05:14:37 EST

On Mon, 2008-10-20 at 09:53 +0200, Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@xxxxxxxx> 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.


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