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

[Tian, Kevin]

> 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?