Re: [PATCH v3 3/3] QEMU-AER: Qemu changes to support AER for VFIO-PCI devices

[Gleb Natapov <gleb@redhat.com>]

On Tue, Feb 05, 2013 at 10:59:41AM +0000, Pandarathil, Vijaymohan R wrote:
> 
> 
> > -----Original Message-----
> > From: Gleb Natapov [mailto:gleb@redhat.com]
> > Sent: Tuesday, February 05, 2013 1:21 AM
> > To: Pandarathil, Vijaymohan R
> > Cc: Blue Swirl; Alex Williamson; Bjorn Helgaas; Ortiz, Lance E;
> > kvm@vger.kernel.org; qemu-devel@nongnu.org; linux-pci@vger.kernel.org;
> > linux-kernel@vger.kernel.org
> > Subject: Re: [PATCH v3 3/3] QEMU-AER: Qemu changes to support AER for VFIO-
> > PCI devices
> > 
> > On Tue, Feb 05, 2013 at 09:05:19AM +0000, Pandarathil, Vijaymohan R wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Gleb Natapov [mailto:gleb@redhat.com]
> > > > Sent: Tuesday, February 05, 2013 12:05 AM
> > > > To: Blue Swirl
> > > > Cc: Pandarathil, Vijaymohan R; Alex Williamson; Bjorn Helgaas; Ortiz,
> > Lance
> > > > E; kvm@vger.kernel.org; qemu-devel@nongnu.org; linux-
> > pci@vger.kernel.org;
> > > > linux-kernel@vger.kernel.org
> > > > Subject: Re: [PATCH v3 3/3] QEMU-AER: Qemu changes to support AER for
> > VFIO-
> > > > PCI devices
> > > >
> > > > On Sun, Feb 03, 2013 at 04:36:11PM +0000, Blue Swirl wrote:
> > > > > On Sun, Feb 3, 2013 at 2:10 PM, Pandarathil, Vijaymohan R
> > > > > <vijaymohan.pandarathil@hp.com> wrote:
> > > > > >         - Create eventfd per vfio device assigned to a guest and
> > > > register an
> > > > > >           event handler
> > > > > >
> > > > > >         - This fd is passed to the vfio_pci driver through the
> > SET_IRQ
> > > > ioctl
> > > > > >
> > > > > >         - When the device encounters an error, the eventfd is
> > signalled
> > > > > >           and the qemu eventfd handler gets invoked.
> > > > > >
> > > > > >         - In the handler decide what action to take. Current action
> > > > taken
> > > > > >           is to terminate the guest.
> > > > >
> > > > > Usually this is not OK, but I guess this is not guest triggerable.
> > > > >
> > > > Still not OK. Why not stop a guest with appropriate stop reason?
> > >
> > > The thinking was that since this is a hardware error, we would want to
> > stop the guest at the earliest. The hw_error() routine which aborts the
> > qemu process was suggested by Alex and that seemed appropriate. Earlier I
> > was using qemu_system_shutdown_request().  Any suggestions ?
> > >
> > I am thinking vm_stop(). Stopping SMP guest (and UP too in fact)
> > involves sending IPIs to other cpus running guest's vcpus. Both exit()
> > and vm_stop() will do it, but former is implicitly in the kernel and
> > later is explicitly in QEMU.
> 
> I had used vm_stop(RUN_STATE_SHUTDOWN) earlier in my code. But while testing, guest ended up in a hang rather than exiting. There seems to some cleanup work which is being done as part of vm_stop. In our case, we wanted the guest to exit immediately. So use of hw_error() seemed appropriate.
> 
What makes you think it hang? It stopped, precisely what it should do if
you call vm_stop(). Now it is possible for vm user to investigate what
happened and even salvage some data from guest memory.

--
			Gleb.