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

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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@xxxxxxxxxx>
> To: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>
> CC: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>,
>  "xieyisheng1@xxxxxxxxxx" <xieyisheng1@xxxxxxxxxx>, "kvm@xxxxxxxxxxxxxxx"
>  <kvm@xxxxxxxxxxxxxxx>, "linux-pci@xxxxxxxxxxxxxxx"
>  <linux-pci@xxxxxxxxxxxxxxx>, "xuzaibo@xxxxxxxxxx" <xuzaibo@xxxxxxxxxx>,
>  Will Deacon <Will.Deacon@xxxxxxx>, "okaya@xxxxxxxxxxxxxx"
>  <okaya@xxxxxxxxxxxxxx>, "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx>,
>  "yi.l.liu@xxxxxxxxx" <yi.l.liu@xxxxxxxxx>, "ashok.raj@xxxxxxxxx"
>  <ashok.raj@xxxxxxxxx>, "tn@xxxxxxxxxxxx" <tn@xxxxxxxxxxxx>,
>  "joro@xxxxxxxxxx" <joro@xxxxxxxxxx>, "robdclark@xxxxxxxxx"
>  <robdclark@xxxxxxxxx>, "bharatku@xxxxxxxxxx" <bharatku@xxxxxxxxxx>,
>  "linux-acpi@xxxxxxxxxxxxxxx" <linux-acpi@xxxxxxxxxxxxxxx>,
>  "liudongdong3@xxxxxxxxxx" <liudongdong3@xxxxxxxxxx>, "rfranz@xxxxxxxxxx"
>  <rfranz@xxxxxxxxxx>, "devicetree@xxxxxxxxxxxxxxx"
>  <devicetree@xxxxxxxxxxxxxxx>, "kevin.tian@xxxxxxxxx"
>  <kevin.tian@xxxxxxxxx>, Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>,
>  "alex.williamson@xxxxxxxxxx" <alex.williamson@xxxxxxxxxx>,
>  "rgummal@xxxxxxxxxx" <rgummal@xxxxxxxxxx>, "thunder.leizhen@xxxxxxxxxx"
>  <thunder.leizhen@xxxxxxxxxx>, "linux-arm-kernel@xxxxxxxxxxxxxxxxxxx"
>  <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, "shunyong.yang@xxxxxxxxxxxxxxxx"
>  <shunyong.yang@xxxxxxxxxxxxxxxx>, "dwmw2@xxxxxxxxxxxxx"
>  <dwmw2@xxxxxxxxxxxxx>, "liubo95@xxxxxxxxxx" <liubo95@xxxxxxxxxx>,
>  "jcrouse@xxxxxxxxxxxxxx" <jcrouse@xxxxxxxxxxxxxx>,
>  "iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx" <iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx>,
>  Robin Murphy <Robin.Murphy@xxxxxxx>, "christian.koenig@xxxxxxx"
>  <christian.koenig@xxxxxxx>, "nwatters@xxxxxxxxxxxxxx"
>  <nwatters@xxxxxxxxxxxxxx>, "baolu.lu@xxxxxxxxxxxxxxx"
>  <baolu.lu@xxxxxxxxxxxxxxx>, liguozhu@xxxxxxxxxxxxx,
>  kenneth-lee-2012@xxxxxxxxxxx
> Subject: Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces
> Message-ID: <20180525093959.000040a7@xxxxxxxxxx>
> Organization: Huawei
> X-Mailer: Claws Mail 3.15.0 (GTK+ 2.24.31; x86_64-w64-mingw32)
> 
> +CC Kenneth Lee
> 
> On Fri, 25 May 2018 09:33:11 +0300
> Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> 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  
> 
> 

(p.s. I sent this mail on May 26 from my public email count. But it
seems the email server is blocked. I resent it from my company count until my
colleague told me just now. Sorry for inconvenience)

-- 
			-Kenneth(Hisilicon)



[Index of Archives]     [DMA Engine]     [Linux Coverity]     [Linux USB]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [Greybus]

  Powered by Linux