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[213.95.11.211]) by mx.google.com with ESMTPS id g187si3076279wmg.188.2019.01.31.00.02.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Jan 2019 00:02:04 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) client-ip=213.95.11.211; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de Received: by newverein.lst.de (Postfix, from userid 2407) id A164168CEB; Thu, 31 Jan 2019 09:02:03 +0100 (CET) Date: Thu, 31 Jan 2019 09:02:03 +0100 From: Christoph Hellwig To: Jerome Glisse Cc: Logan Gunthorpe , Jason Gunthorpe , Christoph Hellwig , "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" Subject: Re: [RFC PATCH 3/5] mm/vma: add support for peer to peer to device vma Message-ID: <20190131080203.GA26495@lst.de> References: <20190129174728.6430-4-jglisse@redhat.com> <20190129191120.GE3176@redhat.com> <20190129193250.GK10108@mellanox.com> <99c228c6-ef96-7594-cb43-78931966c75d@deltatee.com> <20190129205827.GM10108@mellanox.com> <20190130080208.GC29665@lst.de> <20190130174424.GA17080@mellanox.com> <20190130185027.GC5061@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190130185027.GC5061@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) 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 Wed, Jan 30, 2019 at 01:50:27PM -0500, Jerome Glisse wrote: > I do not see how VMA changes are any different than using struct page > in respect to userspace exposure. Those vma callback do not need to be > set by everyone, in fact expectation is that only handful of driver > will set those. > > How can we do p2p between RDMA and GPU for instance, without exposure > to userspace ? At some point you need to tell userspace hey this kernel > does allow you to do that :) To do RDMA on a memory region you need struct page backіng to start with..