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. > > Thanks, > Jean
