From: Nicolin Chen nicolinc@nvidia.com 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?