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Date: Thu, 27 Jul 2017 12:50:42 +0100
From: "Daniel P. Berrange" <berrange@redhat.com>
Message-ID: <20170727115042.GL2555@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH for-2.10 0/3] qdev/vfio: defer DEVICE_DEL
 to avoid races with libvirt
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To: David Gibson <david@gibson.dropbear.id.au>
Cc: Peter Maydell <peter.maydell@linaro.org>, Michael Roth <mdroth@linux.vnet.ibm.com>, QEMU Developers <qemu-devel@nongnu.org>, Alex Williamson <alex.williamson@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Greg Kurz <groug@kaod.org>, Markus Armbruster <armbru@redhat.com>

On Thu, Jul 27, 2017 at 08:53:48PM +1000, David Gibson wrote:
> On Thu, Jul 27, 2017 at 10:11:48AM +0100, Peter Maydell wrote:
> > On 27 July 2017 at 02:30, Michael Roth <mdroth@linux.vnet.ibm.com> wrote:
> > > In particular, Mellanox CX4 adapters on PowerNV hosts might not be fully
> > > quiesced by vfio-pci's finalize() routine until up to 6s after the
> > > DEVICE_DELETED was emitted, leading to detach-device on the libvirt side pretty
> > > much always crashing the host.
> > 
> > My initial naive thought is that if the host kernel can crash then
> > this is a host kernel bug... shouldn't the host kernel refuse
> > the subsequent libvirt rebind if it would cause a crash ?
> 
> I think so too, but I haven't been able to convince Alex.  Nor
> find time to fix it in the kernel myself.

I think we need to fix both the QEMU premature sending of DEVICE_DELETED
and the kernel bug that allowed the crash.

Regards,
Daniel
-- 
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