On Tue, May 04, 2021 at 09:22:55AM -0700, Jacob Pan wrote: > Hi Jason, > > On Wed, 28 Apr 2021 17:46:06 -0300, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > > > > > I think the name IOASID is fine for the uAPI, the kernel version can > > > > be called ioasid_id or something. > > > > > > ioasid is already an id and then ioasid_id just adds confusion. Another > > > point is that ioasid is currently used to represent both PCI PASID and > > > ARM substream ID in the kernel. It implies that if we want to separate > > > ioasid and pasid in the uAPI the 'pasid' also needs to be replaced with > > > another general term usable for substream ID. Are we making the > > > terms too confusing here? > > > > This is why I also am not so sure about exposing the PASID in the API > > because it is ultimately a HW specific item. > > > > As I said to David, one avenue is to have some generic uAPI that is > > very general and keep all this deeply detailed stuff, that really only > > matters for qemu, as part of a more HW specific vIOMMU driver > > interface. > I think it is not just for QEMU. I am assuming you meant PASID is > needed for guest driver to program assigned but not mediated devices. Anything that directly operates the device and tries to instantiate PASIDs for vfio-pci devices will need to understand the PASID. > User space drivers may also need to get the real HW PASID to program it on > to the HW. So this uAPI need to provide some lookup functionality. Perhaps > the kernel generic version can be called ioasid_hw_id? > > So we have the following per my understanding: > - IOASID: a userspace logical number which identifies a page table, this can > be a first level (GVA-GPA), or a second level (GPA->HPA) page table. > - PASID: strictly defined in PCIe term > - Substream ID: strictly defined in ARM SMMUv3 spec. > - IOASID_HW_ID: a generic ID backed by PASID, Substream ID, or any other > HW IDs used to tag DMA > > Is that right? It is reasonable. If a IOASID_HW_ID IOCTL can back with a enum that qualified its exact nature it might be perfectly fine. Jason
