On 16 Nov 2022, at 0:15, Christoph Hellwig wrote: >> + dma_unmap_page_attrs(device, buf->dma, PAGE_SIZE, >> + DMA_BIDIRECTIONAL, >> + DMA_ATTR_SKIP_CPU_SYNC); > >> + addr = dma_map_page_attrs(device, page, 0, PAGE_SIZE, >> + DMA_BIDIRECTIONAL, >> + DMA_ATTR_SKIP_CPU_SYNC); > > You can't just magically skip cpu syncs. The flag is only valid > for mappings of already mapped memory when following a very careful > protocol. I can't see any indications of that beeing true here, > but maybe I'm just missing something. This was copied from page_pool_dma_map(). The same logic applies - io_uring pins the memory, zctap creates a pool that is dma mapped, and the driver performs dma_sync_single_*() when receiving the packet. — Jonathan
