Re: [PATCH v2 4/4] vfio/pci: Allow MMIO regions to be exported through dma-buf

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> +{
> +	struct vfio_pci_dma_buf *priv = dmabuf->priv;
> +	int rc;
> +
> +	rc = pci_p2pdma_distance_many(priv->vdev->pdev, &attachment->dev, 1,
> +				      true);

This should just use pci_p2pdma_distance.

> +	/*
> +	 * Since the memory being mapped is a device memory it could never be in
> +	 * CPU caches.
> +	 */

DMA_ATTR_SKIP_CPU_SYNC doesn't even apply to dma_map_resource, not sure
where this wisdom comes from.

> +	dma_addr = dma_map_resource(
> +		attachment->dev,
> +		pci_resource_start(priv->vdev->pdev, priv->index) +
> +			priv->offset,
> +		priv->dmabuf->size, dir, DMA_ATTR_SKIP_CPU_SYNC);

This is not how P2P addresses are mapped.  You need to use
dma_map_sgtable and have the proper pgmap for it.

The above is just a badly implemented version of the dma-direct
PCI_P2PDMA_MAP_BUS_ADDR case, ignoring mappings through the host
bridge or dma-map-ops interactions.



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