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

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Date:	Tue, 21 Oct 2008 01:22:41 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Rusty Russell <rusty@...tcorp.com.au>
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


* Rusty Russell <rusty@...tcorp.com.au> wrote:

> 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.

we could also add an x86_quirks entry to skip the particular DMI scan 
that is causing problems. Would be nice to avoid it though, and fix 
lguest if possible.

	Ingo
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