> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Tuesday, September 15, 2020 10:29 PM > > > Do they need a device at all? It's not clear to me why RID based > > IOMMU management fits within vfio's scope, but PASID based does not. > > In RID mode vfio-pci completely owns the PCI function, so it is more > natural that VFIO, as the sole device owner, would own the DMA mapping > machinery. Further, the RID IOMMU mode is rarely used outside of VFIO > so there is not much reason to try and disaggregate the API. It is also used by vDPA. > > PASID on the other hand, is shared. vfio-mdev drivers will share the > device with other kernel drivers. PASID and DMA will be concurrent > with VFIO and other kernel drivers/etc. > Looks you are equating PASID to host-side sharing, while ignoring another valid usage that a PASID-capable device is passed through to the guest through vfio-pci and then PASID is used by the guest for guest-side sharing. In such case, it is an exclusive usage in host side and then what is the problem for VFIO to manage PASID given that vfio-pci completely owns the function? Thanks Kevin
