RE: [PATCH v1 3/8] iommufd: Create access in vfio_iommufd_emulated_bind()

[Tian, Kevin]

> From: Tian, Kevin
> Sent: Friday, February 3, 2023 5:24 PM
> 
> > From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> > Sent: Thursday, February 2, 2023 3:05 PM
> >
> > To prepare for an access->ioas replacement, move
> iommufd_access_create()
> > call into vfio_iommufd_emulated_bind(), making it symmetric with the
> > __vfio_iommufd_access_destroy() call in
> vfio_iommufd_emulated_unbind().
> > This means an access is created/destroyed by the bind()/unbind(), and the
> > vfio_iommufd_emulated_attach_ioas() only updates the access->ioas
> pointer.
> >
> > Since there's no longer an ioas_id input for iommufd_access_create(), add
> > a new helper iommufd_access_set_ioas() to set access->ioas. We can later
> > add a "replace" feature simply to the new iommufd_access_set_ioas() too.
> >
> > Leaving the access->ioas in vfio_iommufd_emulated_attach_ioas(),
> however,
> > can introduce some potential of a race condition during pin_/unpin_pages()
> > call where access->ioas->iopt is getting referenced. So, add an ioas_lock
> > to protect it.
> >
> 
> What about introducing another flag e.g. vdev->iommufd_access_attached
> which got set in vfio_iommufd_emulated_attach_ioas() to fulfill what
> vdev->iommufd_access guards today?

Obviously this doesn't work with what 'replace' requires in following
patches. So please just ignore this comment...