On Tue, Apr 18, 2017 at 3:56 PM, Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote: > > > On 18/04/17 04:50 PM, Dan Williams wrote: >> 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. > > I'm not sure I follow -- are you agreeing with me? The dma_map_* needs > to fail for any dma it cannot perform. Which means either all dma_ops > providers need to be p2p aware or this logic has to be in dma_map_* > itself. My point being: you can't rely on an injected dma_op for some > devices to handle the fail case globally. Ah, I see what you're saying now. Yes, we do need something that guarantees any dma mapping implementation that gets a struct page that it does now know how to translate properly fails the request. -- 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
