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

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Message-Id: <200810210948.01108.rusty@rustcorp.com.au>
Date:	Tue, 21 Oct 2008 09:48:00 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	maluta_tiago@...oo.com.br, lguest@...abs.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [Lguest] lguest: unhandled trap

On Monday 20 October 2008 18:22:36 Ingo Molnar wrote:
> * Rusty Russell <rusty@...tcorp.com.au> wrote:
> > On Monday 20 October 2008 12:50:09 Tiago Maluta wrote:
> > > --- On Sun, 10/19/08, Rusty Russell <rusty@...tcorp.com.au> wrote:
> > > > > Hi,
> > > > >
> > > > > I'm using 2.6.27-05323-g26e9a39 and when I try to
> > > >
> > > > use lguest:
> > > > > ~#Documentation/lguest/lguest 128 vmlinux
> > > > > lguest: unhandled trap 14 at 0xc0594f6a (0xff900000)
> > > >
> > > > Yes, I found the same issue.  Does this fix it for you?
> > >
> > > Yes. This code fixed the problem.
> >
> > Thanks.  Ingo, can you push this?
> >
> > Subject: lguest: don't try DMI
> >
> > dmi_scan_machine breaks under lguest; this is the simplest fix (though
> > ugly).  Perhaps this hurts Xen too?
> >
> > Error:
> > 	lguest: unhandled trap 14 at 0xc04edeae (0xffa00000)
> >
> > Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> >
> > diff -r 47449cd8e3d8 drivers/firmware/dmi_scan.c
> > --- a/drivers/firmware/dmi_scan.c	Fri Oct 17 12:14:40 2008 +1100
> > +++ b/drivers/firmware/dmi_scan.c	Fri Oct 17 20:54:30 2008 +1100
> > @@ -369,6 +369,11 @@ void __init dmi_scan_machine(void)
> >  	char __iomem *p, *q;
> >  	int rc;
> >
> > +#ifdef CONFIG_PARAVIRT
> > +	if (strcmp(pv_info.name, "lguest") == 0)
> > +		goto error;
> > +#endif
> > +
>
> hm, could you give some more background please? I'm not subscribed to
> the lguest list and the thread is not Cc:-ed to lkml (Cc:-ed it now).
> The patch looks quite ugly because it adds a special-case.
>
> Was the problem introduced by:
>
> 5649b7c: x86: add DMI quirk for AMI BIOS which corrupts address 0xc000
> during
>
> perhaps?
>
> 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)
>
> (with exceptions for the first 4K perhaps.)
>
> 	Ingo

Yes, after this discussion I'm not even sure why it's triggering: even if 
there's crap in the memory it should not fault.  Digging further.

Cheers,
Rusty.
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