On Wed, Jun 02, 2021 at 04:52:02PM +0800, Jason Wang wrote:

在 2021/6/2 上午4:28, Jason Gunthorpe 写道:

quoted

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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
IOASID_ALLOC_IOASID.:)

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)?

This is intended to be the 'drivers/iommu' subsystem though. I don't
want to see pluggabilit here beyoned what drivers/iommu is providing.

If someone wants to do a something complicated through this interface
then they need to make a drivers/iommu implementation.

Or they need to use the mdev-esque "SW TABLE" mode when their driver
attaches to the interface.

If this is good enough or not for a specific device is an entirely
other question though

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

And if this is done then a kernel function indicating page fault
should be triggered on the ioasid handle that the device has. It is
still drivers/iommu functionality

Jason