kexec/kdump of a kvm guest?

[Mike Snitzer]

On Thu, Jul 24, 2008 at 4:39 AM, Alexander Graf <agraf at suse.de> wrote:
>
> On Jul 24, 2008, at 2:13 AM, Mike Snitzer wrote:
>
>> On Sat, Jul 5, 2008 at 7:20 AM, Avi Kivity <avi at qumranet.com> wrote:
>>>
>>> Mike Snitzer wrote:
>>>>
>>>> My host is x86_64 RHEL5U1 running 2.6.25.4 with kvm-70 (kvm-intel).
>>>>
>>>> When I configure kdump in the guest (running 2.6.22.19) and force a
>>>> crash (with 'echo c > /proc/sysrq-trigger) kexec boots the kdump
>>>> kernel but then the kernel hangs (before it gets to /sbin/init et al).
>>>> On the host, the associated qemu is consuming 100% cpu.
>>>>
>>>> I really need to be able to collect vmcores from my kvm guests.  So
>>>> far I can't (on raw hardware all works fine).
>>>>
>>>>
>>>
>>> I've tested this a while ago and it worked (though I tested regular
>>> kexecs,
>>> not crashes); this may be a regression.
>>>
>>> Please run kvm_stat to see what's happening at the time of the crash.
>>
>> OK, I can look into kvm_stat but I just discovered that just having
>> kvm-intel and kvm loaded into my 2.6.22.19 kernel actually prevents
>
> Is 2.6.22.19 your host or your guest kernel? It's very unlikely that you
> loaded kvm modules in the guest.

Correct, 2.6.22.19 is my host kernel.

>> the host from being able to kexec/kdump too!?  I didn't have any
>> guests running (only the kvm modules were loaded).  As soon as I
>> unloaded the kvm modules kdump worked as expected.
>>
>> Something about kvm is completely breaking kexec/kdump on both the
>> host and guest kernels.
>
> I guess the kexec people would be pretty interested in this as well, so I'll
> just CC them for now.
> As you're stating that the host kernel breaks with kvm modules loaded, maybe
> someone there could give a hint.

OK, I can try using a newer kernel on the host too (e.g. 2.6.25.x) to
see how kexec/kdump of the host fairs when kvm modules are loaded.

On the guest side of things, as I mentioned in my original post,
kexec/kdump wouldn't work within a 2.6.22.19 guest with the host
running 2.6.25.4 (with kvm-70).

Mike