Re: [Xen-devel] lastest xen unstable crash

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.04.12 at 19:37, Francisco Rocha <f.e.liberal-rocha@xxxxxxxxxxxxxxx> 
>>> wrote:
> I was trying to build a new machine but the system keeps rebooting.
> I used the lasted unstable version from xen-unstable.hg.
> 
> I have tried with Fedora 16 (kernel 3.3.0-8) and Xubuntu 11.10 
> (3.0.0.17-generic).
> 
> The output to my serial console is attached.

So as already said by someone else, this is a fault on an XSETBV
instruction. In the kernel this immediately follows the setting of
CR4.OSXSAVE, yet in Xen's emulation code the only way to get
#UD here is that (virtual) CR4 bit is not set; all other failure
paths result in #GP.

The emulation code handling the setting of this CR4 bit, however,
would issue a warning if the kernel was attempting to set a bit
that the hypervisor doesn't allow to be set, yet no such warning
is present in the log you provided (and you're already running at
the highest logging level).

In any case, a fundamental question is whether your CPU has
XSAVE support in the first place, and whether kernel and
hypervisor disagree about that for some reason. Could you
for that purpose post /proc/cpuinfo contents from when running
a native kernel?

Beyond that, adding some tracing to the hypervisor may be
necessary to monitor the Dom0 CR4 writes and maybe how
XSAVE support gets initialized in Xen. Would you be able to do
so on your own, and post the results?

Jan


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