> From: Jean-Philippe Brucker > Sent: Tuesday, February 13, 2018 8:40 PM > > > [...] > >> + > >> +/** > >> + * iommu_sva_device_init() - Initialize Shared Virtual Addressing for a > >> device > >> + * @dev: the device > >> + * @features: bitmask of features that need to be initialized > >> + * @max_pasid: max PASID value supported by the device > >> + * > >> + * Users of the bind()/unbind() API must call this function to initialize all > >> + * features required for SVA. > >> + * > >> + * - If the device should support multiple address spaces (e.g. PCI > PASID), > >> + * IOMMU_SVA_FEAT_PASID must be requested. > > > > I think it is by default assumed when using this API, based on definition of > > SVA. Can you elaborate the situation where this flag can be cleared? > > When passing a device to userspace, you could also share its non-pasid > address space with the process. It requires a new domain type so is left > as a TODO in patch 2/37. I did get requests for this feature, though I > think it was mostly for prototyping. I guess I could remove the flag, and > reintroduce it as IOMMU_SVA_FEAT_NO_PASID later on. sorry I still didn't get the definition of non-pasid address space. Did you mean the GPA/IOVA address space and no_pasid implies actually some default PASID associated? > > [...] > >> + ret = domain->ops->sva_device_init(dev, features, &min_pasid, > >> + &max_pasid); > >> + if (ret) > >> + return ret; > >> + > >> + /* FIXME: racy. Next version should have a mutex (same as fault > >> handler) */ > >> + dev_param->sva_features = features; > >> + dev_param->min_pasid = min_pasid; > >> + dev_param->max_pasid = max_pasid; > > > > what's the point of min_pasid here? > > Arm SMMUv3 uses entry 0 of the PASID table for the default (non-pasid) > context, so it needs to set min_pasid to 1. AMD IOMMU recently added a > similar feature (GIoSup), if I understood correctly. > just for such purpose maybe we should just define a reserved_pasid otherwise there will be some waste if an implementation allows it non-zero. Thanks Kevin
