From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 840CE6B026F for ; Fri, 25 May 2018 02:33:19 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id y82-v6so2723521wmb.5 for ; Thu, 24 May 2018 23:33:19 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id e23-v6sor5866819wra.71.2018.05.24.23.33.16 for (Google Transport Security); Thu, 24 May 2018 23:33:16 -0700 (PDT) Date: Fri, 25 May 2018 09:33:11 +0300 From: Ilias Apalodimas Subject: Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces Message-ID: <20180525063311.GA11605@apalos> References: <20180511190641.23008-1-jean-philippe.brucker@arm.com> <20180511190641.23008-4-jean-philippe.brucker@arm.com> <20180516163117.622693ea@jacob-builder> <20180522094334.71f0e36b@jacob-builder> <20180524115039.GA10260@apalos> <19e82a74-429a-3f86-119e-32b12082d0ff@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <19e82a74-429a-3f86-119e-32b12082d0ff@arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Jean-Philippe Brucker Cc: "xieyisheng1@huawei.com" , "kvm@vger.kernel.org" , "linux-pci@vger.kernel.org" , "xuzaibo@huawei.com" , "jonathan.cameron@huawei.com" , Will Deacon , "okaya@codeaurora.org" , "linux-mm@kvack.org" , "yi.l.liu@intel.com" , "ashok.raj@intel.com" , "tn@semihalf.com" , "joro@8bytes.org" , "robdclark@gmail.com" , "bharatku@xilinx.com" , "linux-acpi@vger.kernel.org" , "liudongdong3@huawei.com" , "rfranz@cavium.com" , "devicetree@vger.kernel.org" , "kevin.tian@intel.com" , Jacob Pan , "alex.williamson@redhat.com" , "rgummal@xilinx.com" , "thunder.leizhen@huawei.com" , "linux-arm-kernel@lists.infradead.org" , "shunyong.yang@hxt-semitech.com" , "dwmw2@infradead.org" , "liubo95@huawei.com" , "jcrouse@codeaurora.org" , "iommu@lists.linux-foundation.org" , Robin Murphy , "christian.koenig@amd.com" , "nwatters@codeaurora.org" , "baolu.lu@linux.intel.com" On Thu, May 24, 2018 at 04:04:39PM +0100, Jean-Philippe Brucker wrote: > On 24/05/18 12:50, Ilias Apalodimas wrote: > >> Interesting, I hadn't thought about this use-case before. At first I > >> thought you were talking about mdev devices assigned to VMs, but I think > >> you're referring to mdevs assigned to userspace drivers instead? Out of > >> curiosity, is it only theoretical or does someone actually need this? > > > > There has been some non upstreamed efforts to have mdev and produce userspace > > drivers. Huawei is using it on what they call "wrapdrive" for crypto devices and > > we did a proof of concept for ethernet interfaces. At the time we choose not to > > involve the IOMMU for the reason you mentioned, but having it there would be > > good. > > I'm guessing there were good reasons to do it that way but I wonder, is > it not simpler to just have the kernel driver create a /dev/foo, with a > standard ioctl/mmap/poll interface? Here VFIO adds a layer of > indirection, and since the mediating driver has to implement these > operations already, what is gained? The best reason i can come up with is "common code". You already have one API doing that for you so we replicate it in a /dev file? The mdev approach still needs extentions to support what we tried to do (i.e mdev bus might need yo have access on iommu_ops), but as far as i undestand it's a possible case. > > Thanks, > Jean