> From: Nicolin Chen <nicolinc@xxxxxxxxxx> > Sent: Wednesday, September 11, 2024 3:08 PM > > On Wed, Sep 11, 2024 at 06:12:21AM +0000, Tian, Kevin wrote: > > > From: Nicolin Chen <nicolinc@xxxxxxxxxx> > > > Sent: Wednesday, August 28, 2024 1:00 AM > > > > > [...] > > > On a multi-IOMMU system, the VIOMMU object can be instanced to the > > > number > > > of vIOMMUs in a guest VM, while holding the same parent HWPT to > share > > > the > > > > Is there restriction that multiple vIOMMU objects can be only created > > on a multi-IOMMU system? > > I think it should be generally restricted to the number of pIOMMUs, > although likely (not 100% sure) we could do multiple vIOMMUs on a > single-pIOMMU system. Any reason for doing that? No idea. But if you stated so then there will be code to enforce it e.g. failing the attempt to create a vIOMMU object on a pIOMMU to which another vIOMMU object is already linked? > > > > stage-2 IO pagetable. Each VIOMMU then just need to only allocate its > own > > > VMID to attach the shared stage-2 IO pagetable to the physical IOMMU: > > > > this reads like 'VMID' is a virtual ID allocated by vIOMMU. But from the > > entire context it actually means the physical 'VMID' allocated on the > > associated physical IOMMU, correct? > > Quoting Jason's narratives, a VMID is a "Security namespace for > guest owned ID". The allocation, using SMMU as an example, should the VMID alone is not a namespace. It's one ID to tag another namespace. > be a part of vIOMMU instance allocation in the host SMMU driver. > Then, this VMID will be used to mark the cache tags. So, it is > still a software allocated ID, while HW would use it too. > VMIDs are physical resource belonging to the host SMMU driver. but I got your original point that it's each vIOMMU gets an unique VMID from the host SMMU driver, not exactly that each vIOMMU maintains its own VMID namespace. that'd be a different concept.
