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

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Date:	Mon, 20 Oct 2008 09:22:36 +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 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
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