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

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Message-ID: <b129f0c1-b61e-4efb-9e25-d8cdadaca1b3@amd.com>
Date: Wed, 21 Jan 2026 10:20:51 +0100
From: Christian König <christian.koenig@....com>
To: Leon Romanovsky <leon@...nel.org>, Sumit Semwal
 <sumit.semwal@...aro.org>, Alex Deucher <alexander.deucher@....com>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Gerd Hoffmann <kraxel@...hat.com>,
 Dmitry Osipenko <dmitry.osipenko@...labora.com>,
 Gurchetan Singh <gurchetansingh@...omium.org>, Chia-I Wu
 <olvaffe@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Jason Gunthorpe <jgg@...pe.ca>,
 Kevin Tian <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Felix Kuehling <Felix.Kuehling@....com>, Alex Williamson <alex@...zbot.org>,
 Ankit Agrawal <ankita@...dia.com>,
 Vivek Kasireddy <vivek.kasireddy@...el.com>
Cc: linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
 amd-gfx@...ts.freedesktop.org, virtualization@...ts.linux.dev,
 intel-xe@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
 iommu@...ts.linux.dev, kvm@...r.kernel.org
Subject: Re: [PATCH v3 6/7] vfio: Wait for dma-buf invalidation to complete

On 1/20/26 15:07, 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>

Reviewed-by: Christian König <christian.koenig@....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);
>