On Thu, Jun 17, 2021 at 02:45:46PM +1000, David Gibson wrote: > On Wed, Jun 09, 2021 at 09:39:19AM -0300, Jason Gunthorpe wrote: > > On Wed, Jun 09, 2021 at 02:24:03PM +0200, Joerg Roedel wrote: > > > On Mon, Jun 07, 2021 at 02:58:18AM +0000, Tian, Kevin wrote: > > > > - Device-centric (Jason) vs. group-centric (David) uAPI. David is not fully > > > > convinced yet. Based on discussion v2 will continue to have ioasid uAPI > > > > being device-centric (but it's fine for vfio to be group-centric). A new > > > > section will be added to elaborate this part; > > > > > > I would vote for group-centric here. Or do the reasons for which VFIO is > > > group-centric not apply to IOASID? If so, why? > > > > VFIO being group centric has made it very ugly/difficult to inject > > device driver specific knowledge into the scheme. > > > > The device driver is the only thing that knows to ask: > > - I need a SW table for this ioasid because I am like a mdev > > - I will issue TLPs with PASID > > - I need a IOASID linked to a PASID > > - I am a devices that uses ENQCMD and vPASID > > - etc in future > > mdev drivers might know these, but shim drivers, like basic vfio-pci > often won't. The generic drivers say 'I will do every kind of DMA possible', which is in-of-itself a special kind of information to convey. There are alot of weird corners to think about here, like what if the guest asks for a PASID on a mdev that doesn't support PASID, but hooked to a RID that does or other quite nonsense combinations. These need to be blocked/handled/whatever properly, which is made much easier if the common code actually knows detail about what is going on. > I still think you're having a tendency to partially conflate several > meanings of "group": > 1. the unavoidable hardware unit of non-isolation > 2. the kernel internal concept and interface to it > 3. the user visible fd and interface I think I have those pretty clearly seperated :) > We can't avoid having (1) somewhere, (3) and to a lesser extent (2) > are what you object to. I don't like (3) either, and am yet to hear a definitive reason why we must have it.. > > The current approach has the group try to guess the device driver > > intention in the vfio type 1 code. > > I agree this has gotten ugly. What I'm not yet convinced of is that > reworking groups to make this not-ugly necessarily requires totally > minimizing the importance of groups. I think it does - we can't have the group in the middle and still put the driver in chrage, it doesn't really work. At least if someone can see an arrangement otherwise lets hear it - start with how to keep groups and remove the mdev hackery from type1.. Jason
