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

[Jonathan Cameron <Jonathan.Cameron-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

+CC Kenneth Lee

On Fri, 25 May 2018 09:33:11 +0300
Ilias Apalodimas <ilias.apalodimas-QSEj5FYQhm4dnm+yROfE0A@public.gmane.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.
> > 
> > Thanks,
> > Jean