From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E357C282D8 for ; Wed, 30 Jan 2019 17:17:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1333F2087F for ; Wed, 30 Jan 2019 17:17:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732459AbfA3RRt (ORCPT ); Wed, 30 Jan 2019 12:17:49 -0500 Received: from ale.deltatee.com ([207.54.116.67]:39494 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726972AbfA3RRt (ORCPT ); Wed, 30 Jan 2019 12:17:49 -0500 Received: from s01061831bf6ec98c.cg.shawcable.net ([68.147.80.180] helo=[192.168.6.205]) by ale.deltatee.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.89) (envelope-from ) id 1gotUV-0006Y7-9V; Wed, 30 Jan 2019 10:17:36 -0700 To: Jason Gunthorpe Cc: Jerome Glisse , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Greg Kroah-Hartman , "Rafael J . Wysocki" , Bjorn Helgaas , Christian Koenig , Felix Kuehling , "linux-pci@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , Christoph Hellwig , Marek Szyprowski , Robin Murphy , Joerg Roedel , "iommu@lists.linux-foundation.org" References: <20190129191120.GE3176@redhat.com> <20190129193250.GK10108@mellanox.com> <99c228c6-ef96-7594-cb43-78931966c75d@deltatee.com> <20190129205749.GN3176@redhat.com> <2b704e96-9c7c-3024-b87f-364b9ba22208@deltatee.com> <20190129215028.GQ3176@redhat.com> <20190129234752.GR3176@redhat.com> <655a335c-ab91-d1fc-1ed3-b5f0d37c6226@deltatee.com> <20190130041841.GB30598@mellanox.com> From: Logan Gunthorpe Message-ID: Date: Wed, 30 Jan 2019 10:17:27 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190130041841.GB30598@mellanox.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 68.147.80.180 X-SA-Exim-Rcpt-To: iommu@lists.linux-foundation.org, jroedel@suse.de, robin.murphy@arm.com, m.szyprowski@samsung.com, hch@lst.de, dri-devel@lists.freedesktop.org, linux-pci@vger.kernel.org, Felix.Kuehling@amd.com, christian.koenig@amd.com, bhelgaas@google.com, rafael@kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, jglisse@redhat.com, jgg@mellanox.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-01-29 9:18 p.m., Jason Gunthorpe wrote: > Every attempt to give BAR memory to struct page has run into major > trouble, IMHO, so I like that this approach avoids that. > > And if you don't have struct page then the only kernel object left to > hang meta data off is the VMA itself. > > It seems very similar to the existing P2P work between in-kernel > consumers, just that VMA is now mediating a general user space driven > discovery process instead of being hard wired into a driver. But the kernel now has P2P bars backed by struct pages and it works well. And that's what we are doing in-kernel. We even have a hacky out-of-tree module which exposes these pages and it also works (but would need Jerome's solution for denying those pages in GUP, etc). So why do something completely different in userspace so they can't share any of the DMA map infrastructure? Logan