Re: dma_map_resource() has a bad performance in pcie peer to peer transactions when iommu enabled in Linux

[Christoph Hellwig]

FYI, dma_map_resources must never be used for PCIe P2P mappings, you
absolutely must use dma_map_sg as only that handles all the corner cases
correctly.

And we need to figure out a way to put a check into dma_map_resources
so that people stop abusing it.