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 <jonathan.came...@huawei.com> > To: Ilias Apalodimas <ilias.apalodi...@linaro.org> > CC: Jean-Philippe Brucker <jean-philippe.bruc...@arm.com>, > "xieyishe...@huawei.com" <xieyishe...@huawei.com>, "k...@vger.kernel.org" > <k...@vger.kernel.org>, "linux-...@vger.kernel.org" > <linux-...@vger.kernel.org>, "xuza...@huawei.com" <xuza...@huawei.com>, > Will Deacon <will.dea...@arm.com>, "ok...@codeaurora.org" > <ok...@codeaurora.org>, "linux...@kvack.org" <linux...@kvack.org>, > "yi.l....@intel.com" <yi.l....@intel.com>, "ashok....@intel.com" > <ashok....@intel.com>, "t...@semihalf.com" <t...@semihalf.com>, > "j...@8bytes.org" <j...@8bytes.org>, "robdcl...@gmail.com" > <robdcl...@gmail.com>, "bhara...@xilinx.com" <bhara...@xilinx.com>, > "linux-a...@vger.kernel.org" <linux-a...@vger.kernel.org>, > "liudongdo...@huawei.com" <liudongdo...@huawei.com>, "rfr...@cavium.com" > <rfr...@cavium.com>, "devicet...@vger.kernel.org" > <devicet...@vger.kernel.org>, "kevin.t...@intel.com" > <kevin.t...@intel.com>, Jacob Pan <jacob.jun....@linux.intel.com>, > "alex.william...@redhat.com" <alex.william...@redhat.com>, > "rgum...@xilinx.com" <rgum...@xilinx.com>, "thunder.leiz...@huawei.com" > <thunder.leiz...@huawei.com>, "linux-arm-ker...@lists.infradead.org" > <linux-arm-ker...@lists.infradead.org>, "shunyong.y...@hxt-semitech.com" > <shunyong.y...@hxt-semitech.com>, "dw...@infradead.org" > <dw...@infradead.org>, "liub...@huawei.com" <liub...@huawei.com>, > "jcro...@codeaurora.org" <jcro...@codeaurora.org>, > "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>, > Robin Murphy <robin.mur...@arm.com>, "christian.koe...@amd.com" > <christian.koe...@amd.com>, "nwatt...@codeaurora.org" > <nwatt...@codeaurora.org>, "baolu...@linux.intel.com" > <baolu...@linux.intel.com>, liguo...@hisilicon.com, > kenneth-lee-2...@foxmail.com > Subject: Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces > Message-ID: <20180525093959.00004...@huawei.com> > > +CC Kenneth Lee > > On Fri, 25 May 2018 09:33:11 +0300 > Ilias Apalodimas <ilias.apalodi...@linaro.org> 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) _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
