On Tue, Apr 18, 2017 at 3:48 PM, Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote: > > > 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. No, we can't do that at get_user_pages() time, it will always need to be up to the device driver to fail dma that it can't perform. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
