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

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Message-ID: <aW/pQmOO8komCgOK@lstrano-desk.jf.intel.com>
Date: Tue, 20 Jan 2026 12:44:50 -0800
From: Matthew Brost <matthew.brost@...el.com>
To: Leon Romanovsky <leon@...nel.org>
CC: Sumit Semwal <sumit.semwal@...aro.org>, Christian König
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Subject: Re: [PATCH v3 6/7] vfio: Wait for dma-buf invalidation to complete

On Tue, Jan 20, 2026 at 04:07:06PM +0200, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.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@...dia.com>
> ---
>  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);

Should we explicitly call out in the dma_buf_move_notify() /
invalidate_mappings kernel-doc that KERNEL slots are the mechanism
for communicating asynchronous dma_buf_move_notify /
invalidate_mappings events via fences?

Yes, this is probably implied, but it wouldn’t hurt to state this
explicitly as part of the cross-driver contract.

Here is what we have now:

 	 * - Dynamic importers should set fences for any access that they can't
	 *   disable immediately from their &dma_buf_attach_ops.invalidate_mappings
 	 *   callback.

Matt

>  			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);
> 
> -- 
> 2.52.0
>