Re: [Qemu-devel] [PATCH 3/3] virtio: set ISR on dataplane notifications

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 15 Nov 2016 19:58:52 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Tue, Nov 15, 2016 at 10:48:15AM -0700, Alex Williamson wrote:
> > On Tue, 15 Nov 2016 19:38:30 +0200
> > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> >   
> > > On Tue, Nov 15, 2016 at 05:22:49PM +0100, Paolo Bonzini wrote:  
> > > > 
> > > > 
> > > > On 15/11/2016 16:44, Michael S. Tsirkin wrote:    
> > > > > True. We could drop it from non-data plane, it's just that we never had
> > > > > a reason to. vhost in kernel does not set ISR in MSI mode, either.    
> > > > 
> > > > Yeah, I suspected that.  But dropping it from non-dataplane would break
> > > > Windows hibernation and crashdump, just like it did for Alex.    
> > > 
> > > I guess it's just a question of updating the drivers,
> > > isn't it? To me, hibernation/crashdump doesn't sound important
> > > enough to warrant work-arounds, but if you feel otherwise,
> > > I'm fine with doing this work-around for dataplane.  
> > 
> > The fact that Windows is trying to do some sort of hibernation is not
> > visible to the user, I'm simply trying to shutdown the VM.  That's
> > rather important on my scale of functionality.  If we have drivers in
> > the wild doing this, does it matter what's in the spec?  
> 
> It matters that latest drivers are already OK. "Update drivers"
> has been the advice for any kind of windows problem for years.
> 
> > Smells like a
> > regression from an end user perspective. Thanks,
> > 
> > Alex  
> 
> This exposes a driver bug, yes. The right fix is easy to point
> out, whether we want a work-around I'm not sure - I understand that
> you feel strongly that we do, is that right? OK, just let's document
> what's going on and which versions are affected.

I don't mind updating my drivers, I'm just guessing that the average
user doesn't know what virtio driver version they're running, doesn't
read release notes, and will be at least slightly annoyed by this
behavior that looks and smells like a regression from v2.7.  If it
hit me, then there are probably others affected as well.  It's up to you
to weigh maintaining not-entirely-spec-complaint behavior vs user angst.
Thanks,

Alex