[Intel-gfx] [PATCH] drm/i915/gvt: Add missing vfio_unregister_group_dev() call

[Tian, Kevin]

> From: Alex Williamson <alex.williamson at redhat.com>
> Sent: Friday, October 7, 2022 2:31 AM
> 
> On Thu, 6 Oct 2022 08:37:09 -0300
> Jason Gunthorpe <jgg at nvidia.com> wrote:
> 
> > On Wed, Oct 05, 2022 at 04:03:56PM -0600, Alex Williamson wrote:
> > > We can't have a .remove callback that does nothing, this breaks
> > > removing the device while it's in use.  Once we have the
> > > vfio_unregister_group_dev() fix below, we'll block until the device is
> > > unused, at which point vgpu->attached becomes false.  Unless I'm
> > > missing something, I think we should also follow-up with a patch to
> > > remove that bogus warn-on branch, right?  Thanks,
> >
> > Yes, looks right to me.
> >
> > I question all the logical arround attached, where is the locking?
> 
> Zhenyu, Zhi, Kevin,
> 
> Could someone please take a look at use of vgpu->attached in the GVT-g
> driver?  It's use in intel_vgpu_remove() is bogus, the .release
> callback needs to use vfio_unregister_group_dev() to wait for the
> device to be unused.  The WARN_ON/return here breaks all future use of
> the device.  I assume @attached has something to do with the page table
> interface with KVM, but it all looks racy anyway.
> 
> Also, whatever purpose vgpu->released served looks unnecessary now.
> Thanks,
> 

Zhi is looking at it.