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

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Message-ID: <bd37adf0-afd0-49c4-b608-7f9aa5994f7b@amd.com>
Date: Mon, 19 Jan 2026 13:12:45 +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>,
 Alex Williamson <alex@...zbot.org>
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 v2 4/4] vfio: Add pinned interface to perform revoke
 semantics

On 1/18/26 13:08, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.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@...dia.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,
>