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

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Message-ID: <F9E001219150CB45BEDC82A650F360C9014B445B@G9W0717.americas.hpqcorp.net>
Date:	Tue, 5 Feb 2013 12:05:11 +0000
From:	"Pandarathil, Vijaymohan R" <vijaymohan.pandarathil@...com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Blue Swirl <blauwirbel@...il.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Ortiz, Lance E" <lance.oritz@...com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 3/3] QEMU-AER: Qemu changes to support AER for
 VFIO-PCI devices



> -----Original Message-----
> From: linux-pci-owner@...r.kernel.org [mailto:linux-pci-
> owner@...r.kernel.org] On Behalf Of Gleb Natapov
> Sent: Tuesday, February 05, 2013 3:37 AM
> To: Pandarathil, Vijaymohan R
> Cc: Blue Swirl; Alex Williamson; Bjorn Helgaas; Ortiz, Lance E;
> kvm@...r.kernel.org; qemu-devel@...gnu.org; linux-pci@...r.kernel.org;
> linux-kernel@...r.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 10:59:41AM +0000, Pandarathil, Vijaymohan R wrote:
> >
> >
> > > -----Original Message-----
> > > From: Gleb Natapov [mailto:gleb@...hat.com]
> > > Sent: Tuesday, February 05, 2013 1:21 AM
> > > To: Pandarathil, Vijaymohan R
> > > Cc: Blue Swirl; Alex Williamson; Bjorn Helgaas; Ortiz, Lance E;
> > > kvm@...r.kernel.org; qemu-devel@...gnu.org; linux-pci@...r.kernel.org;
> > > linux-kernel@...r.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@...hat.com]
> > > > > Sent: Tuesday, February 05, 2013 12:05 AM
> > > > > To: Blue Swirl
> > > > > Cc: Pandarathil, Vijaymohan R; Alex Williamson; Bjorn Helgaas;
> Ortiz,
> > > Lance
> > > > > E; kvm@...r.kernel.org; qemu-devel@...gnu.org; linux-
> > > pci@...r.kernel.org;
> > > > > linux-kernel@...r.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@...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.

That was ignorance on my part on the expected behavior of vm_stop(). 
So what you are suggesting is to stop the guest displaying an appropriate 
error/next-steps message and have the users do any data-collection/investigation 
and then manually kill the guest, if they so desire. Right ?

Sounds reasonable. As long as the guest is not touching the device, it should be okay.
Alex, Any comments ?

Thanks

Vijay

 
> 
> --
> 			Gleb.
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