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From:   "Tian, Kevin" <kevin.tian@intel.com>
To:     David Gibson <david@gibson.dropbear.id.au>
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Subject: RE: [RFC v2] /dev/iommu uAPI proposal
Thread-Topic: [RFC v2] /dev/iommu uAPI proposal
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Date:   Mon, 9 Aug 2021 08:34:06 +0000
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> From: David Gibson <david@gibson.dropbear.id.au>
> Sent: Friday, August 6, 2021 12:45 PM
> > > > In concept I feel the purpose of DMA endpoint is equivalent to the
> routing
> > > > info in this proposal.
> > >
> > > Maybe?  I'm afraid I never quite managed to understand the role of th=
e
> > > routing info in your proposal.
> > >
> >
> > the IOMMU routes incoming DMA packets to a specific I/O page table,
> > according to RID or RID+PASID carried in the packet. RID or RID+PASID
> > is the routing information (represented by device cookie +PASID in
> > proposed uAPI) and what the iommu driver really cares when activating
> > the I/O page table in the iommu.
>=20
> Ok, so yes, endpoint is roughly equivalent to that.  But my point is
> that the IOMMU layer really only cares about that (device+routing)
> combination, not other aspects of what the device is.  So that's the
> concept we should give a name and put front and center in the API.
>=20

This is how this proposal works, centered around the routing info. the=20
uAPI doesn't care what the device is. It just requires the user to specify=
=20
the user view of routing info (device fd + optional pasid) to tag an IOAS.=
=20
the user view is then converted to the kernel view of routing (rid or=20
rid+pasid) by vfio driver and then passed to iommu fd in the attaching=20
operation. and GET_INFO interface is provided for the user to check=20
whether a device supports multiple IOASes and whether pasid space is=20
delegated to the user. We just need a better name if pasid is considered=20
too pci specific...

But creating an endpoint per ioasid and making it centered in uAPI is not=20
what the IOMMU layer cares about.

Thanks
Kevin