Re: [PATCH v2 4/4] vfio: Add pinned interface to perform revoke semantics

["Christian König" <christian.koenig@amd.com>]

On 1/18/26 13:08, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@nvidia.com>
> 
> DMABUF ->pin() interface is called when the DMABUF importer perform
> its DMA mapping, so let's use this opportunity to check if DMABUF
> exporter revoked its buffer or not.
> 
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> ---
>  drivers/vfio/pci/vfio_pci_dmabuf.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
> index d4d0f7d08c53..af9c315ddf71 100644
> --- a/drivers/vfio/pci/vfio_pci_dmabuf.c
> +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
> @@ -20,6 +20,20 @@ struct vfio_pci_dma_buf {
>  	u8 revoked : 1;
>  };
>  
> +static int vfio_pci_dma_buf_pin(struct dma_buf_attachment *attachment)
> +{
> +	struct vfio_pci_dma_buf *priv = attachment->dmabuf->priv;
> +
> +	dma_resv_assert_held(priv->dmabuf->resv);
> +
> +	return dma_buf_attachment_is_revoke(attachment) ? 0 : -EOPNOTSUPP;

It's probably better to do that check in vfio_pci_dma_buf_attach.

And BTW the function vfio_pci_dma_buf_move() seems to be broken:

void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
{
        struct vfio_pci_dma_buf *priv;
        struct vfio_pci_dma_buf *tmp;

        lockdep_assert_held_write(&vdev->memory_lock);

        list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) {
                if (!get_file_active(&priv->dmabuf->file))
                        continue;

                if (priv->revoked != revoked) {
                        dma_resv_lock(priv->dmabuf->resv, NULL);
                        priv->revoked = revoked;
                        dma_buf_move_notify(priv->dmabuf);

A dma_buf_move_notify() just triggers asynchronous invalidation of the mapping!

You need to use dma_resv_wait() to wait for that to finish.

                        dma_resv_unlock(priv->dmabuf->resv);
                }
                fput(priv->dmabuf->file);
        }
}

Regards,
Christian.


> +}
> +
> +static void vfio_pci_dma_buf_unpin(struct dma_buf_attachment *attachment)
> +{
> +	/* Do nothing */
> +}
> +
>  static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,
>  				   struct dma_buf_attachment *attachment)
>  {
> @@ -76,6 +90,8 @@ static void vfio_pci_dma_buf_release(struct dma_buf *dmabuf)
>  }
>  
>  static const struct dma_buf_ops vfio_pci_dmabuf_ops = {
> +	.pin = vfio_pci_dma_buf_pin,
> +	.unpin = vfio_pci_dma_buf_unpin,
>  	.attach = vfio_pci_dma_buf_attach,
>  	.map_dma_buf = vfio_pci_dma_buf_map,
>  	.unmap_dma_buf = vfio_pci_dma_buf_unmap,
>