Introduce the helper function ib_dma_pci_p2p_dma_supported() to check if a given ib_device can be used in P2PDMA transfers. This ensures the ib_device is not using virt_dma and also that the underlying dma_device supports P2PDMA. Use the new helper in nvme-rdma to replace the existing check for ib_uses_virt_dma(). Adding the dma_pci_p2pdma_supported() check allows switching away from pci_p2pdma_[un]map_sg(). Signed-off-by: Logan Gunthorpe <logang@deltatee.com> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Reviewed-by: Max Gurtovoy <mgurtovoy@nvidia.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Christoph Hellwig <hch@lst.de>