Messages in this thread | | | From | "Tian, Kevin" <> | Subject | Plan for /dev/ioasid RFC v2 | Date | Mon, 7 Jun 2021 02:58:18 +0000 |
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Hi, all,
We plan to work on v2 now, given many good comments already received and substantial changes envisioned. This is a very complex topic with many sub-threads being discussed. To ensure that I didn't miss valuable suggestions (and also keep everyone on the same page), here I'd like to provide a list of planned changes in my mind. Please let me know if anything important is lost. :)
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(Remaining opens in v1)
- Protocol between kvm/vfio/ioasid for wbinvd/no-snoop. I'll see how much can be refined based on discussion progress when v2 is out;
- Device-centric (Jason) vs. group-centric (David) uAPI. David is not fully convinced yet. Based on discussion v2 will continue to have ioasid uAPI being device-centric (but it's fine for vfio to be group-centric). A new section will be added to elaborate this part;
- PASID virtualization (section 4) has not been thoroughly discussed yet. Jason gave some suggestion on how to categorize intended usages. I will rephrase this section and hope more discussions can be held for it in v2;
(Adopted suggestions)
- (Jason) Rename /dev/ioasid to /dev/iommu (so does uAPI e.g. IOASID _XXX to IOMMU_XXX). One suggestion (Jason) was to also rename RID+PASID to SID+SSID. But given the familiarity of the former, I will still use RID+PASID in v2 to ease the discussoin;
- (Jason) v1 prevents one device from binding to multiple ioasid_fd's. This will be fixed in v2;
- (Jean/Jason) No need to track guest I/O page tables on ARM/AMD. When a pasid table is bound, it becomes a container for all guest I/O page tables;
- (Jean/Jason) Accordingly a device label is required so iotlb invalidation and fault handling can both support per-device operation. Per Jean's suggestion, this label will come from userspace (when VFIO_BIND_ IOASID_FD);
- (Jason) Addition of device label allows per-device capability/format check before IOASIDs are created. This leads to another major uAPI change in v2 - specify format info when creating an IOASID (mapping protocol, nesting, coherent, etc.). User is expected to check per-device format and then set proper format for IOASID upon to-be-attached device;
- (Jason/David) No restriction on map/unmap vs. bind/invalidate. They can be used in either parent or child;
- (David) Change IOASID_GET_INFO to report permitted range instead of reserved IOVA ranges. This works better for PPC;
- (Jason) For helper functions, expect to have explicit bus-type wrappers e.g. ioasid_pci_device_attach;
(Not adopted)
- (Parav) Make page pinning a syscall; - (Jason. W/Enrico) one I/O page table per fd; - (David) Replace IOASID_REGISTER_MEMORY through another ioasid nesting (sort of passthrough mode). Need more thinking. v2 will not change this part;
Thanks Kevin
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