These patches allow for user-space transfers between NVMe solid-state drives in a more efficient manner via P2PDMA . The patches though at the moment are marked "request for comments" and there are some technical issues to overcome around scatter-gather lists (SGLs) and one of the DMA interfaces.
The P2PDMA code works with AMD hardware while Intel support is coming soon and DMA-direct implementations. Other IOMMU implementations like ARM and POWER are forthcoming.
More details on this P2PDMA support between NVMe drives via this patch series .