Re: [RFC] /dev/ioasid uAPI proposal

From: Jason Wang
Date: Wed Jun 02 2021 - 04:52:45 EST

在 2021/6/2 上午4:28, Jason Gunthorpe 写道:
I summarized five opens here, about:

1) Finalizing the name to replace /dev/ioasid;
2) Whether one device is allowed to bind to multiple IOASID fd's;
3) Carry device information in invalidation/fault reporting uAPI;
4) What should/could be specified when allocating an IOASID;
5) The protocol between vfio group and kvm;

For 1), two alternative names are mentioned: /dev/iommu and
/dev/ioas. I don't have a strong preference and would like to hear
votes from all stakeholders. /dev/iommu is slightly better imho for
two reasons. First, per AMD's presentation in last KVM forum they
implement vIOMMU in hardware thus need to support user-managed
domains. An iommu uAPI notation might make more sense moving
forward. Second, it makes later uAPI naming easier as 'IOASID' can
be always put as an object, e.g. IOMMU_ALLOC_IOASID instead of
I think two years ago I suggested /dev/iommu and it didn't go very far
at the time.

It looks to me using "/dev/iommu" excludes the possibility of implementing IOASID in a device specific way (e.g through the co-operation with device MMU + platform IOMMU)?

What's more, ATS spec doesn't forbid the device #PF to be reported via a device specific way.


We've also talked about this as /dev/sva for a while and
now /dev/ioasid

I think /dev/iommu is fine, and call the things inside them IOAS

Then we don't have naming aliasing with kernel constructs.