On 17/05/18 00:31, Jacob Pan wrote: > On Fri, 11 May 2018 20:06:04 +0100 > I am a little confused about domain vs. pasid relationship. If > each domain represents a address space, should there be a domain for > each pasid? I don't think there is a formal definition, but from previous discussion the consensus seems to be: domains are a collection of devices that have the same virtual address spaces (one or many). Keeping that definition makes things easier, in my opinion. Some time ago, I did try to represent PASIDs using "subdomains" (introducing a hierarchy of struct iommu_domain), but it required invasive changes in the IOMMU subsystem and probably all over the tree. You do need some kind of "root domain" for each device, so that "iommu_get_domain_for_dev()" still makes sense. That root domain doesn't have a single address space but a collection of subdomains. If you need this anyway, representing a PASID with an iommu_domain doesn't seem preferable than using a different structure (io_mm), because they don't have anything in common. Thanks, Jean
