On Wed, Sep 11, 2024 at 08:13:01AM +0000, Tian, Kevin wrote: > > > > Yes, many more patches, and don't try to do it now.. But we can copy > > > > the vmid from the s2 and place it in the viommu struct during > > > > allocation time. > > > > > > > > > > does it assume that a viommu object cannot span multiple physical > > > IOMMUs so there is only one vmid per viommu? > > > > I think so. One the reasons of introducing vIOMMU is to maintain > > the shareability across physical IOMMUs at the s2 HWPT_PAGING. > > > > I don't quite get it. e.g. for intel-iommu the S2 domain itself can > be shared across physical IOMMUs SMMU does the same, but needs a VMID per pSMMU to tag that S2 domain: vIOMMU0 (VMIDx of pSMMU0) -> shared S2 vIOMMU1 (VMIDy of pSMMU1) -> shared S2 Note: x and y might be different. > then what is the problem > preventing a vIOMMU object using that S2 to span multiple IOMMUs? Jason previously suggested the way of implementing multi-vIOMMU in a VMM to be one vIOMMU object representing a vIOMMU instance (of a physical IOMMU) in the VM. So, it'd be only one VMID per one vIOMMU object. Sharing one vIOMMU object on the other hand needs the vIOMMU to hold a list of VMIDs for all (or attached?) physical IOMMUs. This would change what a vIOMMU object represents. > Probably there is a good reason e.g. for simplification or better > aligned with hw accel stuff. But it's not explained clearly so far. I will try emphasizing that in the next version, likely in the rst file that I am patching for HWPT_PAGING/NESTED at this point. Thanks Nicolin
