> From: Liu, Yi L <yi.l.liu@xxxxxxxxx> > Sent: Thursday, December 12, 2024 3:13 PM > > On 2024/12/12 13:51, Tian, Kevin wrote: > >> From: Liu, Yi L <yi.l.liu@xxxxxxxxx> > >> Sent: Thursday, December 12, 2024 11:15 AM > >> > >> So maybe we should not stick with the initial purpose of ALLOC_PASID flag. > >> It actually means selecting V2 page table. But the definition of it allows > >> us to consider the nested domains to be pasid-compat as Intel allows it. > >> And, a sane userspace running on ARM/AMD will never attach nested > >> domain > >> to PASIDs. Even it does, the ARM SMMU and AMD iommu driver can fail > such > >> attempts. In this way, we can enforce the ALLOC_PASID flag for any > domains > >> used by PASID-capable devices in iommufd. This suits the existing > >> ALLOC_PASID definition as well. > > > > Isn't it what I was suggesting? IOMMUFD just enforces that flag must > > be set if a domain will be attached to PASID, and drivers will do > > additional restrictions e.g. AMD/ARM allows the flag only on paging > > domain while VT-d allows it for any type. > > A slight difference. :) I think we also need to enforce it for the > non-PASID path. If not, the PASID path cannot work according to the > ALLOC_PASID definition. But we are on the same page about the additional > restrictions in ARM/AMD drivers about the nested domain used on PASIDs. > This is supposed to be done in attach phase instead of domain allocation > time. > Here is my full picture: At domain allocation the driver should decide whether the setting of ALLOC_PASID is compatible to the given domain type. If paging and iommu supports pasid then ALLOC_PASID is allowed. This applies to all drivers. AMD driver will further select V1 vs. V2 according to the flag bit. If nesting, AMR/ARM drivers will reject the bit as a CD/PASID table cannot be attached to a PASID. Intel driver allows it if pasid is supported by iommu. At attach phase, a domain with ALLOC_PASID can be attached to RID of any device no matter the device supports pasid or not. But a domain must have ALLOC_PASID set for attaching to a PASID (if the device has non-zero max_pasids), enforced by iommufd.
