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Re: [Xen-devel] Crashing Xen

To: Jacob Gorm Hansen <jacob@xxxxxxxx>
Subject: Re: [Xen-devel] Crashing Xen
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 06 Jan 2004 18:03:19 +0000
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
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> hi,
> I am trying to create a custom domain from code based on
> xc_linux_build.c.
> While I do not expect my newly instantiated domain to happily execute
> whatever code I have for it at this stage, I am a bit surprised that
> instead of just silently dying, it takes all of Xen with it, and the
> machine reboots once I start my newly constructed domain.

Hmmm... well, I was reasonably careful to ensure that there is sanity
checking within Xen when building a domain to ensure that the domain
cannot crash the whole machine. This may not be perfect, however, and
xc_linux_build runs with enough privilege to hose the machine :-( We
want to look at making domain building require fewer privileges
sometime soon.

> The start operation completes and returns without error, but as soon as
> the domain is scheduled (it appears) the machine crashes.
> I have tried to instrument the Xen code with various printks (I have a
> serial line connected) and apparently the switch_to function completes
> without errors. I suppose that with enough printks I will eventually
> find the troubled spot, but I was hoping that a little advice as to
> where to look would ease my burdens.
> What parameters to the build- and start-domain syscalls should I be
> extra careful with, and where in Xen will bad domain parameters most
> likely cause a crash?

Which Xen tree are you developing on? 1.2 or 1.3?

You should turn on debugging in xen/arch/i386/Rules.mk. If you are
running on a newer Xen then that will also turn on all DPRINTKs
automatically. Thus you may get some error messages before you crash.

How different is your domain builder from the default one? Perhaps a
better place to look is just at what you do that is different?

Basically, I think you'll need to find this one via tracing! If you
find anywhere in Xen that could be better sanity-checked then let me
know and I'll patch it.


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