IOASID set token

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

Hi Jean,

Have a question for you on whether we can have a fixed token type for
ioasid_set.

Currently, ioasid_set has an arbitrary token. For VT-d vSVA usage, we
choose mm as ioasid_set token to identify PASIDs within a guest. We have
multiple in-kernel users of PASIDs such as VFIO, KVM, and VDCM. When an
IOASID set is created, there is not a good way to communicate about the
token choices. So we have to let VDCM and KVM *assume* mm is used as
token, then retrieve ioasid_set based on the token.

This assumption of "mm as token" is not a reliable SW architecture. So
we are thinking if we can have an explicit ioasid_set token type where
mm is used. After all, PASID and mm are closely related.

The code change might be the following:
1. add a flag to indicate token type when ioasid_set is allocated, e.g.
IOASID_SET_TYPE_MM
IOASID_SET_TYPE_ANY
2. other users of the ioasid_set can query if an mm token exists based
on the flag IOASID_SET_TYPE_MM, then retrieve the ioasid_set.

Existing ioasid_set user can still use arbitrary token under the flag
IOASID_SET_TYPE_ANY

Would this be an issue for ARM usage?

Thanks,

Jacob
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