On Thu, Jun 20, 2019 at 10:12:16AM -0600, Logan Gunthorpe wrote: > It is expected the creator of the dma-direct bio will ensure the > target device can access the DMA address it's creating bios for. > It's also not possible to bounce a dma-direct bio seeing the block > layer doesn't have any way to access the underlying data behind > the DMA address. > > Thus, never bounce dma-direct bios. I wonder how feasible it would be to implement a 'dma vec' copy from/to? That is about the only operation you could safely do on P2P BAR memory. I wonder if a copy implementation could somehow query the iommu layer to get a kmap of the memory pointed at by the dma address so we don't need to carry struct page around? Jason
