On Thu, Jun 17, 2021 at 08:10:04PM -0300, Jason Gunthorpe wrote: > 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.. I don't know that there's a "definitive" reason. My concern (and I think Alex's as well) is that if there's no (3), it tends to lead to a lack of (2), and lack of (2) tends to make people sloppily forget about (1) and lead to breakage. > > > 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 > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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