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

[Alex Williamson]

On Tue, 15 Nov 2016 21:17:56 +0200
"Michael S. Tsirkin" <address@hidden> wrote:

> On Tue, Nov 15, 2016 at 11:21:55AM -0700, Alex Williamson wrote:
> > On Tue, 15 Nov 2016 19:58:52 +0200
> > "Michael S. Tsirkin" <address@hidden> 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" <address@hidden> 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  
> 
> I think I'll merge the work-around if it's better documented.
> If you think it should go in, can you provide your tested-by tag?
> 

Tested series against 97e53cf82ca0ffa9abe2def2fabc5fc75b914d90, solves
both the vhost issue and the hung shutdown on my VM.

Tested-by: Alex Williamson <address@hidden>