On Sat, May 26, 2018 at 10:24:45AM +0800, Kenneth Lee wrote:
> Date: Sat, 26 May 2018 10:24:45 +0800
> From: Kenneth Lee <kenneth-lee-2...@foxmail.com>
> To: Jonathan Cameron <jonathan.came...@huawei.com>
> Cc: Ilias Apalodimas <ilias.apalodi...@linaro.org>, Jean-Philippe Brucker
> <jean-philippe.bruc...@arm.com>, "xieyishe...@huawei.com"
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> Subject: Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces
> Message-ID: <20180526022445.GA6069@kllp05>
>
> 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)
I just found this mail was missed in the mailing list. I tried it once
again.
--
-Kenneth Lee (Hisilicon)
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