On Fri, May 24, 2024 at 05:24:11AM +0000, Tian, Kevin wrote: > > > > > > On Tue, May 14, 2024 at 06:59:07PM -0700, Nicolin Chen wrote: > > > > > > > So, you want a proxy S1 domain for a device to attach, in case > > > > > > > of a stage-2 only setup, because an S2 domain will no longer has > > > > > > > a VMID, since it's shared among viommus. In the SMMU driver case, > > > > > > > an arm_smmu_domain won't have an smmu pointer, so a device > > can't > > > > > > > attach to an S2 domain but always an nested S1 domain, right? > > > > > > > > > > > > That seems like a simple solution to the VMID lifetime, but it means > > > > > > the kernel has to decode more types of vSTE. > > And the narrative at the top was trying to describe the links: > > [ device ] => [ proxy identity S1 ] => [ viommu [ shared S2 ] ] > > v.s. > > [ device ] => [ non-shareable S2 ] > > > > So the first case can take advantage of VIOMMU_INVALIDATE v.s. > > the second case requires a DEV_INVALIDATE. > > and one side-effect in the first case is to save one VMID for > non-shareable S2 hence improves iotlb efficiency. Hmm, how is that? VMID is currently stored in an S2 domain, actually. The viommu is a VMID holder to potentially decouple VMID from S2 domain, because VMID is per SMMU instance while S2 domain is shareable: [ dev0 ] => [ S1 dom0 ] => [ viommu0 (VMID0) [ shared S2 ] ] [ dev1 ] => [ S1 dom1 ] => [ viommu1 (VMID1) [ shared S2 ] ] By the way, we can also have (very likely our initial version): [ dev0 ] => [ S1 dom0 ] => [ viommu0 [ non-sharable S2 dom0 (VMID0) ] ] [ dev1 ] => [ S1 dom1 ] => [ viommu1 [ non-sharable S2 dom1 (VMID1) ] ] Thanks Nicolin
