Debuging dom0, oops while kexec

Debuging dom0, oops while kexec

[Daniil Cherednik]

Hello!

We use ubuntu 12.04 on dom0 xen-4.1, linux-3.5
We have some issue with our hardware driver, and I need to get dom0 
coredump. But when I was trying to configure kdump it was unsuccessful 
and I used kexec -l ... to diagnostic the issue I got oops like 
http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1807
Also I noticed recently it was discussing about implementation kexec 
mechanism in hypervisor without involving dom0 kernel...
So I will be grateful if someone can take me any advises about using 
kexec with xen and about bug1807

Best regards,
Daniil Cherednik

Re: Debuging dom0, oops while kexec

[Andrew Cooper]

On 21/06/13 13:01, Daniil Cherednik wrote:
> Hello!
>
> We use ubuntu 12.04 on dom0 xen-4.1, linux-3.5
> We have some issue with our hardware driver, and I need to get dom0
> coredump. But when I was trying to configure kdump it was unsuccessful
> and I used kexec -l ... to diagnostic the issue I got oops like
> http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1807
> Also I noticed recently it was discussing about implementation kexec
> mechanism in hypervisor without involving dom0 kernel...
> So I will be grateful if someone can take me any advises about using
> kexec with xen and about bug1807
>
> Best regards,
> Daniil Cherednik

First of all, you want -p for a crash kernel, not -l (which is a load
kernel).

That link shows a linux-3.5 bug.  At a guess machine_kexec_prepare is
not suitably sanitising some pointers before trying to use them.

There are patch series for Xen (and libxc) and kexec tools.  The Xen
patch series is being deferred until Xen 4.4 development starts.  The
kexec tools series also needs to wait until the libxc patches are available.

The slight problem with this approach is that you need to patch the
kernel to unconditionally issue a kexec hypercall as it no longer knows
whether a crash image has been loaded or not.

~Andrew

>
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> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

Re: Debuging dom0, oops while kexec

[David Vrabel]

On 21/06/13 13:01, Daniil Cherednik wrote:
> Hello!
> 
> We use ubuntu 12.04 on dom0 xen-4.1, linux-3.5
> We have some issue with our hardware driver, and I need to get dom0
> coredump. But when I was trying to configure kdump it was unsuccessful

This is expected -- kexec from a Xen guest is not supported by upstream
Linux.

> and I used kexec -l ... to diagnostic the issue I got oops like
> http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1807

Is it really like that one?  That oops dates back to a 2.6.32 kernel.

> Also I noticed recently it was discussing about implementation kexec
> mechanism in hypervisor without involving dom0 kernel...

Yes there is.  See the list archives.  Note that there are some bugs in
the latest version that was posted and I haven't yet had time to post an
updated patch series.

David