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 <[email protected]> > To: Ilias Apalodimas <[email protected]> > CC: Jean-Philippe Brucker <[email protected]>, > "[email protected]" <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" <[email protected]>, > Will Deacon <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" <[email protected]>, > "[email protected]" <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" <[email protected]>, > "[email protected]" <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" <[email protected]>, > "[email protected]" <[email protected]>, > "[email protected]" <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" > <[email protected]>, Jacob Pan <[email protected]>, > "[email protected]" <[email protected]>, > "[email protected]" <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" <[email protected]>, > "[email protected]" <[email protected]>, > "[email protected]" <[email protected]>, > Robin Murphy <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" > <[email protected]>, "[email protected]" > <[email protected]>, [email protected], > [email protected] > Subject: Re: [PATCH v2 03/40] iommu/sva: Manage process address spaces > Message-ID: <[email protected]> > 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 <[email protected]> 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) _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
