linux-kernel - Re: [RESEND][PATCH 2/2 v3] deal with guest panicked event

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Date:	Thu, 8 Mar 2012 11:56:56 +0000
From:	"Daniel P. Berrange" <berrange@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Wen Congyang <wency@...fujitsu.com>,
	kvm list <kvm@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Gleb Natapov <gleb@...hat.com>
Subject: Re: [RESEND][PATCH 2/2 v3] deal with guest panicked event

On Thu, Mar 08, 2012 at 01:52:45PM +0200, Avi Kivity wrote:
> On 03/08/2012 01:36 PM, Daniel P. Berrange wrote:
> > On Thu, Mar 08, 2012 at 01:28:56PM +0200, Avi Kivity wrote:
> > > On 03/08/2012 12:15 PM, Wen Congyang wrote:
> > > > When the host knows the guest is panicked, it will set
> > > > exit_reason to KVM_EXIT_GUEST_PANICKED. So if qemu receive
> > > > this exit_reason, we can send a event to tell management
> > > > application that the guest is panicked and set the guest
> > > > status to RUN_STATE_PANICKED.
> > > >
> > > > Signed-off-by: Wen Congyang <wency@...fujitsu.com>
> > > > ---
> > > >  kvm-all.c        |    5 +++++
> > > >  monitor.c        |    3 +++
> > > >  monitor.h        |    1 +
> > > >  qapi-schema.json |    2 +-
> > > >  qmp.c            |    3 ++-
> > > >  vl.c             |    1 +
> > > >  6 files changed, 13 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/kvm-all.c b/kvm-all.c
> > > > index 77eadf6..b3c9a83 100644
> > > > --- a/kvm-all.c
> > > > +++ b/kvm-all.c
> > > > @@ -1290,6 +1290,11 @@ int kvm_cpu_exec(CPUState *env)
> > > >                      (uint64_t)run->hw.hardware_exit_reason);
> > > >              ret = -1;
> > > >              break;
> > > > +        case KVM_EXIT_GUEST_PANICKED:
> > > > +            monitor_protocol_event(QEVENT_GUEST_PANICKED, NULL);
> > > > +            vm_stop(RUN_STATE_PANICKED);
> > > > +            ret = -1;
> > > > +            break;
> > > >
> > > 
> > > If the management application is not aware of this event, then it will
> > > never resume the guest, so it will appear hung.
> >
> > Even if the mgmt app doesn't know about the QEVENT_GUEST_PANICKED, it should
> > still see a QEVENT_STOP event emitted by vm_stop() surely ? So it will
> > know the guest CPUs have been stopped, even if it isn't aware of the
> > reason why, which seems fine to me.
> 
> No.  The guest is stopped, and there's no reason to suppose that the
> management app will restart it.  Behaviour has changed.
> 
> Suppose the guest has reboot_on_panic set; now the behaviour change is
> even more visible - service will stop completely instead of being
> interrupted for a bit while the guest reboots.

Hmm, so this calls for a new command line argument to control behaviour,
similar to what we do for disk werror, eg something like

  --onpanic "report|pause|stop|..."

where

 report - emit QEVENT_GUEST_PANICKED only
 pause  - emit QEVENT_GUEST_PANICKED and pause VM
 stop   - emit QEVENT_GUEST_PANICKED and quit VM
 stop   - emit QEVENT_GUEST_PANICKED and quit VM

This would map fairly well into libvirt, where we already have config
parameters for controlling what todo with a guest when it panics.

Regards,
Daniel
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