Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752265AbdDNM4K (ORCPT <rfc822;w@1wt.eu>);
        Fri, 14 Apr 2017 08:56:10 -0400
Received: from gate.crashing.org ([63.228.1.57]:45038 "EHLO gate.crashing.org"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751235AbdDNM4I (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 14 Apr 2017 08:56:08 -0400
Message-ID: <1492169879.25766.4.camel@kernel.crashing.org>
Subject: Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Logan Gunthorpe <logang@deltatee.com>,
        Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
        Bjorn Helgaas <helgaas@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>,
        "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Jens Axboe <axboe@kernel.dk>, Steve Wise <swise@opengridcomputing.com>,
        Stephen Bates <sbates@raithlin.com>, Max Gurtovoy <maxg@mellanox.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Keith Busch <keith.busch@intel.com>, linux-pci@vger.kernel.org,
        linux-scsi@vger.kernel.org, linux-nvme@lists.infradead.org,
        linux-rdma@vger.kernel.org, linux-nvdimm@ml01.01.org,
        linux-kernel@vger.kernel.org, Jerome Glisse <jglisse@redhat.com>
Date: Fri, 14 Apr 2017 21:37:59 +1000
In-Reply-To: <08c32f0d-6c7c-b65f-6453-dde0d7c173d1@deltatee.com>
References: <1490911959-5146-1-git-send-email-logang@deltatee.com>
         <1491974532.7236.43.camel@kernel.crashing.org>
         <5ac22496-56ec-025d-f153-140001d2a7f9@deltatee.com>
         <1492034124.7236.77.camel@kernel.crashing.org>
         <81888a1e-eb0d-cbbc-dc66-0a09c32e4ea2@deltatee.com>
         <20170413232631.GB24910@bhelgaas-glaptop.roam.corp.google.com>
         <20170414041656.GA30694@obsidianresearch.com>
         <08c32f0d-6c7c-b65f-6453-dde0d7c173d1@deltatee.com>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.22.6 (3.22.6-1.fc25) 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 864
Lines: 27

On Thu, 2017-04-13 at 22:40 -0600, Logan Gunthorpe wrote:
> 
> On 13/04/17 10:16 PM, Jason Gunthorpe wrote:
> > I'd suggest just detecting if there is any translation in bus
> > addresses anywhere and just hard disabling P2P on such systems.
> 
> That's a fantastic suggestion. It simplifies things significantly.
> Unless there are any significant objections I think I will plan on
> doing
> that.

I object.

> > On modern hardware with 64 bit BARs there is very little reason to
> > have translation, so I think this is a legacy feature.
> 
> Yes, p2pmem users are likely to be designing systems around it (ie
> JBOFs) and not trying to shoehorn it onto legacy architectures.
> 
> At the very least, it makes sense to leave it out and if someone
> comes
> along who cares they can put in the effort to support the address
> translation.
> 
> Thanks,
> 
> Logan