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Would it be reasonable to >>> support page faults for nested domains? >> >> yeah, it's good to discuss it. >> >>> If so, perhaps it's time to open intel_iommu_domain_alloc_nested() to >>> support IOMMU_HWPT_FAULT_ID_VALID when PRI is enabled on the device? >> >> IMHO, the PRQ support for nested domains requires some more facility. PRQ >> can happen at either stage-1 or stage-2, iommu driver may need to tell >> it and forward to the correct domain (nested domain or parent domain). Or >> the stage-2 is always pinned just as the VFIO/iommufd does. Hence, any PRQ >> happens under nested translation should be due to stage-1. > > The parent domain is currently always pinned and does not yet support > page faults. Therefore, when a page fault occurs within a nested domain, > it apparently should be routed to user space... > > If we decide to support page faults on the stage-2 domain in the future, > we will need to figure out the correct destination of each page fault > and route it accordingly, either to the parent domain or the user space > nested domain. Hardware assistance would be beneficial, otherwise the > software may need to traverse the parent domain, which is not > performance friendly. this is my question. Is it still true the parent domain is always pinned after the below series? If yes, then it's fine to enable IOPF for nested domain. https://lore.kernel.org/linux-iommu/20241015-jag-iopfv8-v4-0-b696ca89ba29@kernel.org/ -- Regards, Yi Liu