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

[Michael S. Tsirkin]

On Thu, Nov 17, 2016 at 04:04:26AM -0500, Paolo Bonzini wrote:
> > > > > > /*
> > > > > >  * virtio spec 1.0 says ISR bit 0 should be ignored with MSI, but
> > > > > >  * windows drivers included in virtio-win 1.8.0 (circa 2015)
> > > > > >  * for Windows 8.1 only are incorrectly polling this bit during
> > > > > >  shutdown
> > > > >          ^^^^^^^^^^^^^^^^
> > > > > 
> > > > > Not sure it's only for Windows 8.1, in fact probably not.
> > > > 
> > > > 8.1 on shutdown and others on crashdump or hibernation?
> > > 
> > > Even 8.1 is really a hibernation hidden behind a "Shut down" menu item.
> > > 
> > > Paolo
> > 
> > what does "hang during shutdown" in your commit log refer to then?
> 
> The full text from the commit log is:
> 
>     recent releases of
>     Windows do not really shut down, but rather log out and hibernate to
>     make the next startup faster.  Hence, this manifested as a more serious
>     hang during shutdown with e.g. Windows 8.1 and virtio-win 1.8.0 RPMs.
> 
> Shutdown in the commit log just means "clicking Shut down".  The previous
> sentence explains why.  Also note the "e.g.", I've not tested other versions
> of Windows.
> 
> Paolo

AFAIK the specific version of drivers did not support windows 10,
and IIRC windows 7 does shutdown normally.
So that only leaves windows 8 and 8.1.


> > > > > Looks good if you replace this line with
> > > > > 
> > > > > "are incorrectly polling this bit during crashdump or hibernation"

... which on windows 8 and 8.1 is activated by default through the
shutdown menu

> > > > > Paolo
> > > > > 
> > > > > >  * in MSI mode, causing a hang if this bit is never updated.
> > > > > >  * Next driver release from 2016 fixed this problem, so working
> > > > > >  around it
> > > > > >  * is not a must, but it's easy to do so let's do it here.
> > > > > >  *
> > > > > >  * Note: it's safe to update ISR from any thread as it was switched
> > > > > >  * to an atomic operation.
> > > > > >  */
> > > > >