From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kenneth Lee Subject: Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces Date: Sat, 26 May 2018 10:24:45 +0800 Message-ID: <24808.9390145198$1527301495@news.gmane.org> 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> <20180525063311.GA11605@apalos> <20180525093959.000040a7@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20180525093959.000040a7@huawei.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Jonathan Cameron Cc: "xieyisheng1@huawei.com" , "liubo95@huawei.com" , "kvm@vger.kernel.org" , "linux-pci@vger.kernel.org" , "xuzaibo@huawei.com" , Will Deacon , "okaya@codeaurora.org" , "linux-mm@kvack.org" , liguozhu@hisilicon.com, "yi.l.liu@intel.com" , "ashok.raj@intel.com" , Jean-Philippe Brucker , "tn@semihalf.com" , "joro@8bytes.org" , "iommu@lists.linux-foundation.org" , "bharatku@xilinx.com" , "linux-acpi@vger.kernel.org" , "liudongdong3@huawei.com" , "rfranz@cavium.com" , devic List-Id: devicetree@vger.kernel.org On Fri, May 25, 2018 at 09:39:59AM +0100, Jonathan Cameron wrote: > Date: Fri, 25 May 2018 09:39:59 +0100 > From: Jonathan Cameron > To: Ilias Apalodimas > CC: Jean-Philippe Brucker , > "xieyisheng1@huawei.com" , "kvm@vger.kernel.org" > , "linux-pci@vger.kernel.org" > , "xuzaibo@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" > , liguozhu@hisilicon.com, > kenneth-lee-2012@foxmail.com > Subject: Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces > Message-ID: <20180525093959.000040a7@huawei.com> > > +CC Kenneth Lee > > On Fri, 25 May 2018 09:33:11 +0300 > Ilias Apalodimas wrote: > > > 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. Hi, Jean, Please allow me to share my understanding here: https://zhuanlan.zhihu.com/p/35489035 The reason we do not use the /dev/foo scheme is that the devices to be shared are programmable accelerators. We cannot fix up the kernel driver for them. > > > > > > Thanks, > > > Jean > > -- -Kenneth Lee (Hisilicon)