Re: [PATCH v3 6/7] vfio: Wait for dma-buf invalidation to complete

Christian König
2026-01-21T09:21:03Z

On 1/20/26 15:07, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@nvidia.com>
>
> dma-buf invalidation is performed asynchronously by hardware, so VFIO must
> wait until all affected objects have been fully invalidated.
>
> Fixes: 5d74781ebc86 ("vfio/pci: Add dma-buf export support for MMIO regions")
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>

Reviewed-by: Christian König <christian.koenig@amd.com>

Please also keep in mind that the while this wait for all fences for correctness you also need to keep the mapping valid until dma_buf_unmap_attachment() was called.

In other words you can only redirect the DMA-addresses previously given out into nirvana (or a dummy memory or similar), but you still need to avoid re-using them for something else.

Regards,
Christian.

> ---
> drivers/vfio/pci/vfio_pci_dmabuf.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c
> index d4d0f7d08c53..33bc6a1909dd 100644
> --- a/drivers/vfio/pci/vfio_pci_dmabuf.c
> +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c
> @@ -321,6 +321,9 @@ void vfio_pci_dma_buf_move(struct vfio_pci_core_device *vdev, bool revoked)
> dma_resv_lock(priv->dmabuf->resv, NULL);
> priv->revoked = revoked;
> dma_buf_move_notify(priv->dmabuf);
> + dma_resv_wait_timeout(priv->dmabuf->resv,
> + DMA_RESV_USAGE_KERNEL, false,
> + MAX_SCHEDULE_TIMEOUT);
> dma_resv_unlock(priv->dmabuf->resv);
> }
> fput(priv->dmabuf->file);
> @@ -342,6 +345,8 @@ void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev)
> priv->vdev = NULL;
> priv->revoked = true;
> dma_buf_move_notify(priv->dmabuf);
> + dma_resv_wait_timeout(priv->dmabuf->resv, DMA_RESV_USAGE_KERNEL,
> + false, MAX_SCHEDULE_TIMEOUT);
> dma_resv_unlock(priv->dmabuf->resv);
> vfio_device_put_registration(&vdev->vdev);
> fput(priv->dmabuf->file);
>