Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces

[Kenneth Lee <Kenneth-Lee-2012@foxmail.com>]

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-2012@foxmail.com>
> To: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>, Jean-Philippe Brucker
>  <jean-philippe.brucker@arm.com>, "xieyisheng1@huawei.com"
>  <xieyisheng1@huawei.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
>  "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
>  "xuzaibo@huawei.com" <xuzaibo@huawei.com>, Will Deacon
>  <Will.Deacon@arm.com>, "okaya@codeaurora.org" <okaya@codeaurora.org>,
>  "linux-mm@kvack.org" <linux-mm@kvack.org>, "yi.l.liu@intel.com"
>  <yi.l.liu@intel.com>, "ashok.raj@intel.com" <ashok.raj@intel.com>,
>  "tn@semihalf.com" <tn@semihalf.com>, "joro@8bytes.org" <joro@8bytes.org>,
>  "robdclark@gmail.com" <robdclark@gmail.com>, "bharatku@xilinx.com"
>  <bharatku@xilinx.com>, "linux-acpi@vger.kernel.org"
>  <linux-acpi@vger.kernel.org>, "liudongdong3@huawei.com"
>  <liudongdong3@huawei.com>, "rfranz@cavium.com" <rfranz@cavium.com>,
>  "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
>  "kevin.tian@intel.com" <kevin.tian@intel.com>, Jacob Pan
>  <jacob.jun.pan@linux.intel.com>, "alex.williamson@redhat.com"
>  <alex.williamson@redhat.com>, "rgummal@xilinx.com" <rgummal@xilinx.com>,
>  "thunder.leizhen@huawei.com" <thunder.leizhen@huawei.com>,
>  "linux-arm-kernel@lists.infradead.org"
>  <linux-arm-kernel@lists.infradead.org>, "shunyong.yang@hxt-semitech.com"
>  <shunyong.yang@hxt-semitech.com>, "dwmw2@infradead.org"
>  <dwmw2@infradead.org>, "liubo95@huawei.com" <liubo95@huawei.com>,
>  "jcrouse@codeaurora.org" <jcrouse@codeaurora.org>,
>  "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
>  Robin Murphy <Robin.Murphy@arm.com>, "christian.koenig@amd.com"
>  <christian.koenig@amd.com>, "nwatters@codeaurora.org"
>  <nwatters@codeaurora.org>, "baolu.lu@linux.intel.com"
>  <baolu.lu@linux.intel.com>, liguozhu@hisilicon.com
> 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.Cameron@huawei.com>
> > To: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> > CC: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
> >  "xieyisheng1@huawei.com" <xieyisheng1@huawei.com>, "kvm@vger.kernel.org"
> >  <kvm@vger.kernel.org>, "linux-pci@vger.kernel.org"
> >  <linux-pci@vger.kernel.org>, "xuzaibo@huawei.com" <xuzaibo@huawei.com>,
> >  Will Deacon <Will.Deacon@arm.com>, "okaya@codeaurora.org"
> >  <okaya@codeaurora.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>,
> >  "yi.l.liu@intel.com" <yi.l.liu@intel.com>, "ashok.raj@intel.com"
> >  <ashok.raj@intel.com>, "tn@semihalf.com" <tn@semihalf.com>,
> >  "joro@8bytes.org" <joro@8bytes.org>, "robdclark@gmail.com"
> >  <robdclark@gmail.com>, "bharatku@xilinx.com" <bharatku@xilinx.com>,
> >  "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
> >  "liudongdong3@huawei.com" <liudongdong3@huawei.com>, "rfranz@cavium.com"
> >  <rfranz@cavium.com>, "devicetree@vger.kernel.org"
> >  <devicetree@vger.kernel.org>, "kevin.tian@intel.com"
> >  <kevin.tian@intel.com>, Jacob Pan <jacob.jun.pan@linux.intel.com>,
> >  "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
> >  "rgummal@xilinx.com" <rgummal@xilinx.com>, "thunder.leizhen@huawei.com"
> >  <thunder.leizhen@huawei.com>, "linux-arm-kernel@lists.infradead.org"
> >  <linux-arm-kernel@lists.infradead.org>, "shunyong.yang@hxt-semitech.com"
> >  <shunyong.yang@hxt-semitech.com>, "dwmw2@infradead.org"
> >  <dwmw2@infradead.org>, "liubo95@huawei.com" <liubo95@huawei.com>,
> >  "jcrouse@codeaurora.org" <jcrouse@codeaurora.org>,
> >  "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
> >  Robin Murphy <Robin.Murphy@arm.com>, "christian.koenig@amd.com"
> >  <christian.koenig@amd.com>, "nwatters@codeaurora.org"
> >  <nwatters@codeaurora.org>, "baolu.lu@linux.intel.com"
> >  <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 <ilias.apalodimas@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)