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[207.54.116.67]) by mx.google.com with ESMTPS id t4si1566179itj.95.2019.01.30.11.46.03 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 30 Jan 2019 11:46:04 -0800 (PST) Received-SPF: pass (google.com: domain of logang@deltatee.com designates 207.54.116.67 as permitted sender) client-ip=207.54.116.67; Authentication-Results: mx.google.com; spf=pass (google.com: domain of logang@deltatee.com designates 207.54.116.67 as permitted sender) smtp.mailfrom=logang@deltatee.com 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 1govny-0008PD-5M; Wed, 30 Jan 2019 12:45:51 -0700 To: Jason Gunthorpe , Christoph Hellwig 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" , Marek Szyprowski , Robin Murphy , Joerg Roedel , "iommu@lists.linux-foundation.org" References: <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> <20190130080006.GB29665@lst.de> <20190130190651.GC17080@mellanox.com> From: Logan Gunthorpe Message-ID: <840256f8-0714-5d7d-e5f5-c96aec5c2c05@deltatee.com> Date: Wed, 30 Jan 2019 12:45:46 -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: <20190130190651.GC17080@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, 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, hch@lst.de, 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) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2019-01-30 12:06 p.m., Jason Gunthorpe wrote: >> Way less problems than not having struct page for doing anything >> non-trivial. If you map the BAR to userspace with remap_pfn_range >> and friends the mapping is indeed very simple. But any operation >> that expects a page structure, which is at least everything using >> get_user_pages won't work. > > GUP doesn't work anyhow today, and won't work with BAR struct pages in > the forseeable future (Logan has sent attempts on this before). I don't recall ever attempting that... But patching GUP for special pages or VMAS; or working around by not calling it in some cases seems like the thing that's going to need to be done one way or another. > Jerome made the HMM mirror API use this flow, so afer his patch to > switch the ODP MR to use HMM, and to switch GPU drivers, it will work > for those cases. Which is more than the zero cases than we have today > :) But we're getting the same bait and switch here... If you are using HMM you are using struct pages, but we're told we need this special VMA hack for cases that don't use HMM and thus don't have struct pages... Logan