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

[Jason Gunthorpe <jgg@nvidia.com>]

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