On Fri, May 24, 2024 at 07:21:59AM +0000, Tian, Kevin wrote: > My point was based on Jason's example about 3 VMIDs: > > hwpt_alloc(deva, nesting_parent=true) = shared_s2 > viommu_alloc(deva, shared_s2) = viommu1 > viommu_alloc(devb, shared_s2) = viommu2 > hwpt_alloc(deva, viommu1, vste) = deva_vste > hwpt_alloc(devb, viommu2, vste) = devb_vste > attach(deva, deva_vste) > attach(devb, devb_vste) > attach(devc, shared_s2) > > for devc it could be: > hwpt_alloc(deva, viommu1, vproxy_s1) = devc_proxys1 > attach(devc, devc_proxys1) > > then devc will reuse VMID of viommu1 and we save one VMID. I think that can work, at least I haven't thought of a reason why the non-vIOMMU device's VMID couldn't be shared with one of the vIOMMUs. It is all quite a contrived case, I dont't expect people to want to do anything like this, it is just showing that the API is properly setup that it could be done. Userspace is not restricted to a single VIOMMU. > Does that not work so we need create another viommu to hold the > proxy identity s1 then still need a 3rd VMID? Yes, I think that can be OK. Jason
