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

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

On Thu, 6 Oct 2022 08:37:09 -0300
Jason Gunthorpe <jgg@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,

Alex