Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757580AbdDRWst (ORCPT ); Tue, 18 Apr 2017 18:48:49 -0400 Received: from ale.deltatee.com ([207.54.116.67]:55040 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755946AbdDRWso (ORCPT ); Tue, 18 Apr 2017 18:48:44 -0400 To: Dan Williams 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> 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 From: Logan Gunthorpe Message-ID: <5e68102d-e165-6ef3-8678-9bdb4f78382b@deltatee.com> Date: Tue, 18 Apr 2017 16:48:40 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.111 X-SA-Exim-Rcpt-To: jglisse@redhat.com, linux-kernel@vger.kernel.org, linux-nvdimm@ml01.01.org, linux-rdma@vger.kernel.org, linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, linux-pci@vger.kernel.org, keith.busch@intel.com, maxg@mellanox.com, sbates@raithlin.com, swise@opengridcomputing.com, axboe@kernel.dk, martin.petersen@oracle.com, jejb@linux.vnet.ibm.com, sagi@grimberg.me, hch@lst.de, helgaas@kernel.org, benh@kernel.crashing.org, jgunthorpe@obsidianresearch.com, dan.j.williams@intel.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory X-SA-Exim-Version: 4.2.1 (built Mon, 26 Dec 2011 16:24:06 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1329 Lines: 29 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