Re: [Qemu-devel] pvpanic plans?

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 31, 2013 at 08:49:08AM -0600, Eric Blake wrote:
> On 10/31/2013 08:47 AM, Michael S. Tsirkin wrote:
> 
> >>>      if (event & PVPANIC_PANICKED) {
> >>>          panicked_mon_event("pause");
> >>> -        vm_stop(RUN_STATE_GUEST_PANICKED);
> >>
> >> Don't you still need to halt the guest on a panic event, for management
> >> to have a chance to choose what to do about the panic?
> > 
> > Guest can just call hlt to do this. Most guests do this on a panic
> > already.
> 
> On the one hand, the fact that the guest already has to inform the host
> means we are already trusting the guest behavior on a panic.  On the
> other hand, assuming that the guest will ALWAYS halt after triggering a
> panic is putting a lot more trust in the guest, compared to qemu
> explicitly halting the guest so that management has a chance to choose
> to dump the guest's state at the moment the panic was flagged.

I wouldn't call it *a lot* more trust. And again, this is guest policy:
if you want to do hlt from driver because you think it's safer, go for it.

> The biggest argument for either removing all auto-pvpanic, or reverting
> pvpanic altogether, is that no one seems to be actively using pvpanic in
> the field yet.  I wish we could get more feedback from Fujitsu as the
> original patch authors on what they are looking for in a working
> solution, rather than repeatedly second-guessing everything downstream
> and delaying the eradication of the buggy behavior even longer.


With my patch we have a benign device that merely reports io writes
on the monitor. No code -> no bugs.


> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>