On 18/04/17 04:28 PM, Dan Williams wrote: > Unlike the pci bus address offset case which I think is fundamental to > support since shipping archs do this today, I think it is ok to say > p2p is restricted to a single sgl that gets to talk to host memory or > a single device. That said, what's wrong with a p2p aware map_sg > implementation calling up to the host memory map_sg implementation on > a per sgl basis? I think Ben said they need mixed sgls and that is where this gets messy. I think I'd prefer this too given trying to enforce all sgs in a list to be one type or another could be quite difficult given the state of the scatterlist code. >> Also, what happens if p2p pages end up getting passed to a device that >> doesn't have the injected dma_ops? > > This goes back to limiting p2p to a single pci host bridge. If the p2p > capability is coordinated with the bridge rather than between the > individual devices then we have a central point to catch this case. Not really relevant. If these pages get to userspace (as people seem keen on doing) or a less than careful kernel driver they could easily get into the dma_map calls of devices that aren't even pci related (via an O_DIRECT operation on an incorrect file or something). The common code must reject these and can't rely on an injected dma op. Logan
