Re: [Qemu-devel] [PATCH v11] kvm: notify host when the guest is panicked

[Hu Tao <hutao@cn.fujitsu.com>]

On Wed, Nov 21, 2012 at 11:39:28AM +0200, Gleb Natapov wrote:
> On Tue, Nov 20, 2012 at 07:33:49PM -0200, Marcelo Tosatti wrote:
> > On Tue, Nov 20, 2012 at 06:09:48PM +0800, Hu Tao wrote:
> > > Hi Marcelo,
> > > 
> > > On Tue, Nov 13, 2012 at 12:19:08AM -0200, Marcelo Tosatti wrote:
> > > > On Fri, Nov 09, 2012 at 03:17:39PM -0500, Sasha Levin wrote:
> > > > > On Mon, Nov 5, 2012 at 8:58 PM, Hu Tao <hutao@cn.fujitsu.com> wrote:
> > > > > > But in the case of panic notification, more dependency means more
> > > > > > chances of failure of panic notification. Say, if we use a virtio device
> > > > > > to do panic notification, then we will fail if: virtio itself has
> > > > > > problems, virtio for some reason can't be deployed(neither built-in or
> > > > > > as a module), or guest doesn't support virtio, etc.
> > > > > 
> > > > > Add polling to your virtio device. If it didn't notify of a panic but
> > > > > taking more than 20 sec to answer your poll request you can assume
> > > > > it's dead.
> > > > > 
> > > > > Actually, just use virtio-serial and something in userspace on the guest.
> > > > 
> > > > They want the guest to stop, so a memory dump can be taken by management
> > > > interface.
> > > > 
> > > > Hu Tao, lets assume port I/O is the preferred method for communication.
> > > 
> > > Okey.
> > > 
> > > > Now, the following comments have still not been addressed:
> > > > 
> > > > 1) Lifecycle of the stopped guest and interaction with other stopped
> > > > states in QEMU.
> > > 
> > > Patch 3 already deals with run state transitions. But in case I'm
> > > missing something, could you be more specific?
> > 
> > - What are the possibilities during migration? Say:
> > 	- migration starts.
> > 	- guest panics.
> > 	- migration starts vm on other side?
> > - Guest stopped due to EIO.
> > 	- guest vcpuN panics, VMEXIT but still outside QEMU.
> > 	- QEMU EIO error, stop vm.
> > 	- guest vcpuN completes, processes IO exit.
> >         - system_reset due to panic.
> > - Add all possibilities that should be verified (that is, interaction 
> > of this feature with other stopped states in QEMU).

Thank you for your explanation!

> > 
> BTW I do remember getting asserts while using breakpoints via gdbstub
> and stop/cont from the monitor.

Thanks, I'll consider this too.

> 
> > ---
> > 
> > - What happens if the guest has reboot-on-panic configured? Does it take
> > precedence over hypervisor notification?

Yes. But I don't think this is what we want if pv-event is on. Users may
want to do whatever they want when the guest is panicked, but not an automatic
reboot-on-panic. What's your opinion?

> > 
> > 
> > 
> > Out of curiosity, does kexec support memory dumping?

Yes. do we have to disable kexec if pv-event is on, too?

> > 
> > > > 2) Format of the interface for other architectures (you can choose
> > > > a different KVM supported architecture and write an example).
> > > > 
> > > > 3) Clear/documented management interface for the feature.
> > > 
> > > It is documented in patch 0: Documentation/virtual/kvm/pv_event.txt.
> > > Does it need to be improved?
> > 
> > This is documentation for the host<->guest interface. There is no 
> > documentation on the interface for management.

Oh yes, I'll add this.


-- 
Thanks,
Hu Tao