On Mon, Jan 08, 2024 at 04:07:12AM +0000, Tian, Kevin wrote: > > > In concept w/o vSVA it's still possible to assign sibling vdev's to > > > a same VM as each vdev is allocated with a unique pasid to mark vRID > > > so can be differentiated from each other in the fault/error path. > > > > I thought the SIOV plan was that each "vdev" ie vpci function would > > get a slice of the pRID's PASID space statically selected at creation? > > > > So SVA/etc doesn't matter, you reliably get a disjoint set of pRID & > > pPASID into each VM. > > > > From that view you can't identify the iommufd dev_id without knowing > > both the pRID and pPASID which will disambiguate the different SIOV > > iommufd dev_id instances sharing a rid. > > true when assigning those instances to different VMs. > > Here I was talking about assigning them to a same VM being a problem. > with rid sharing plus same ENQCMD pPASID potentially used on both > instances there'd be ambiguity in vSVA e.g. iopf to identify dev_id. Oh you imaging sharing the pPASID if things have the same translation? I guess I can see why, but given where things are overall I'd say just don't do that. Indeed we can't do that because it makes the vRID unknowable. (again I continue to think that vt-d cache design is messed up, using the PASID for the cache tag is a *terrible* design, and causes exactly these kinds of problems) > for errors related to descriptor fetch the driver can tell the command > by looking at the head pointer of the invalidation queue. > > command completion is indirectly detected by inserting a wait descriptor > as fence. completion timeout error is reported in an error register. but > this register doesn't record pasid, nor does the command location. if there > are multiple pending devtlb invalidation commands upon timeout > error the spec suggests the driver to treat all of them timeout as the > register can only record one rid. Makes sense, or at least you have to re-issue them one by one > this is kind of moot. If the driver submits only one command (plus wait) > at a time it doesn't need hw's help to identify the timeout command. > If the driver batches invalidation commands it must treat all timeout if > an timeout error is reported. Yes > from this angle whether to record pasid doesn't really matter. At least for error handling.. Jason
