On Wed, Sep 11, 2024 at 07:18:10AM +0000, Tian, Kevin wrote: > > 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? Yea, I can do that. > > > > 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. Yes. Just the lifecycle of a VMID is controlled by a vIOMMU, i.e. the guest. > 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. What's a VMID namespace actually? Please educate me :) Thanks Nicolin
