[Linaro-mm-sig] Re: [PATCH v5 9/9] vfio/pci: Add dma-buf export support for MMIO regions

On Mon, Oct 13, 2025 at 06:26:11PM +0300, Leon Romanovsky wrote:

+static int vfio_pci_dma_buf_attach(struct dma_buf *dmabuf,

• 		   struct dma_buf_attachment *attachment)
  

+{

• struct vfio_pci_dma_buf *priv = dmabuf->priv;
• if (!attachment->peer2peer)

• return -EOPNOTSUPP;
  

• if (priv->revoked)

• return -ENODEV;
  

• switch (pci_p2pdma_map_type(priv->provider, attachment->dev)) {
• case PCI_P2PDMA_MAP_THRU_HOST_BRIDGE:

• break;
  

• case PCI_P2PDMA_MAP_BUS_ADDR:

• /*
  

•  * There is no need in IOVA at all for this flow.
  

•  * We rely on attachment->priv == NULL as a marker
  

•  * for this mode.
  

•  */
  

• return 0;
  

• default:

• return -EINVAL;
  

• }
• attachment->priv = kzalloc(sizeof(struct dma_iova_state), GFP_KERNEL);
• if (!attachment->priv)

• return -ENOMEM;
  

• dma_iova_try_alloc(attachment->dev, attachment->priv, 0, priv->size);

The lifetime of this isn't good..

• return 0;

+}

+static void vfio_pci_dma_buf_detach(struct dma_buf *dmabuf,

• 		    struct dma_buf_attachment *attachment)
  

+{

• kfree(attachment->priv);

+}

If the caller fails to call map then it leaks the iova.

+static struct sg_table * +vfio_pci_dma_buf_map(struct dma_buf_attachment *attachment,

•      enum dma_data_direction dir)
  

+{

[..]

+err_unmap_dma:

• if (!i || !state)

• ; /* Do nothing */
  

• else if (dma_use_iova(state))

• dma_iova_destroy(attachment->dev, state, mapped_len, dir,
  

• 		 attrs);
  

If we hit this error path then it is freed..

+static void vfio_pci_dma_buf_unmap(struct dma_buf_attachment *attachment,

• 		   struct sg_table *sgt,
  

• 		   enum dma_data_direction dir)
  

+{

• struct vfio_pci_dma_buf *priv = attachment->dmabuf->priv;
• struct dma_iova_state *state = attachment->priv;
• unsigned long attrs = DMA_ATTR_MMIO;
• struct scatterlist *sgl;
• int i;
• if (!state)

• ; /* Do nothing */
  

• else if (dma_use_iova(state))

• dma_iova_destroy(attachment->dev, state, priv->size, dir,
  

• 		 attrs);
  

It is freed here too, but we can call map multiple times. Every time a move_notify happens can trigger another call to map.

I think just call unlink in those two and put dma_iova_free in detach

Jason