Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757867AbdDRWuq (ORCPT ); Tue, 18 Apr 2017 18:50:46 -0400 Received: from mail-oi0-f42.google.com ([209.85.218.42]:34692 "EHLO mail-oi0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757820AbdDRWun (ORCPT ); Tue, 18 Apr 2017 18:50:43 -0400 MIME-Version: 1.0 In-Reply-To: <5e68102d-e165-6ef3-8678-9bdb4f78382b@deltatee.com> References: <1492381396.25766.43.camel@kernel.crashing.org> <20170418164557.GA7181@obsidianresearch.com> <20170418190138.GH7181@obsidianresearch.com> <20170418210339.GA24257@obsidianresearch.com> <20170418212258.GA26838@obsidianresearch.com> <96198489-1af5-abcf-f23f-9a7e41aa17f7@deltatee.com> <5e68102d-e165-6ef3-8678-9bdb4f78382b@deltatee.com> From: Dan Williams Date: Tue, 18 Apr 2017 15:50:41 -0700 Message-ID: Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory To: Logan Gunthorpe Cc: Jason Gunthorpe , Benjamin Herrenschmidt , Bjorn Helgaas , Christoph Hellwig , Sagi Grimberg , "James E.J. Bottomley" , "Martin K. Petersen" , Jens Axboe , Steve Wise , Stephen Bates , Max Gurtovoy , Keith Busch , linux-pci@vger.kernel.org, linux-scsi , linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, linux-nvdimm , "linux-kernel@vger.kernel.org" , Jerome Glisse Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1569 Lines: 31 On Tue, Apr 18, 2017 at 3:48 PM, Logan Gunthorpe 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.