Re: [PATCH v3 1/2] vfio: Replace the DMA unmapping notifier with a callback

Alex Williamson
2022-07-07T21:37:22Z

On Mon, 4 Jul 2022 21:59:03 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:
> diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
> index b49e2e9db2dc6f..09e0ce7b72324c 100644
> --- a/drivers/s390/cio/vfio_ccw_ops.c
> +++ b/drivers/s390/cio/vfio_ccw_ops.c
> @@ -44,31 +44,19 @@ static int vfio_ccw_mdev_reset(struct vfio_ccw_private *private)
> return ret;
> }
>
> -static int vfio_ccw_mdev_notifier(struct notifier_block *nb,
> - unsigned long action,
> - void *data)
> +static void vfio_ccw_dma_unmap(struct vfio_device *vdev, u64 iova, u64 length)
> {
> struct vfio_ccw_private *private =
> - container_of(nb, struct vfio_ccw_private, nb);
> -
> - /*
> - * Vendor drivers MUST unpin pages in response to an
> - * invalidation.
> - */
> - if (action == VFIO_IOMMU_NOTIFY_DMA_UNMAP) {
> - struct vfio_iommu_type1_dma_unmap *unmap = data;
> -
> - if (!cp_iova_pinned(&private->cp, unmap->iova))
> - return NOTIFY_OK;
> + container_of(vdev, struct vfio_ccw_private, vdev);
>
> - if (vfio_ccw_mdev_reset(private))
> - return NOTIFY_BAD;
> + /* Drivers MUST unpin pages in response to an invalidation. */
> + if (!cp_iova_pinned(&private->cp, iova))
> + return;
>
> - cp_free(&private->cp);
> - return NOTIFY_OK;
> - }
> + if (vfio_ccw_mdev_reset(private))
> + return;
>
> - return NOTIFY_DONE;
> + cp_free(&private->cp);
> }

The cp_free() call is gone here with [1], so I think this function now
just ends with:

...
vfio_ccw_mdev_reset(private);
}

There are also minor contextual differences elsewhere from that series,
so a quick respin to record the changes on list would be appreciated.

However the above kind of highlights that NOTIFY_BAD that silently gets
dropped here. I realize we weren't testing the return value of the
notifier call chain and really we didn't intend that notifiers could
return a failure here, but does this warrant some logging or suggest
future work to allow a device to go offline here? Thanks.

Alex

[1]https://lore.kernel.org/all/20220707135737.720765-1-farman@linux.ibm.com/