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From:   "Liu, Yi L" <yi.l.liu@intel.com>
To:     Stefan Hajnoczi <stefanha@gmail.com>
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Subject: RE: [PATCH v3 02/14] iommu: Report domain nesting info
Thread-Topic: [PATCH v3 02/14] iommu: Report domain nesting info
Thread-Index: AQHWSgRQVmc9Qp+Xi0mQEumzIJrE0qjvWjsAgAAviUA=
Date:   Mon, 29 Jun 2020 12:23:08 +0000
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Hi Stefan,

> From: Stefan Hajnoczi <stefanha@gmail.com>
> Sent: Monday, June 29, 2020 5:25 PM
>=20
> On Wed, Jun 24, 2020 at 01:55:15AM -0700, Liu Yi L wrote:
> > +/*
> > + * struct iommu_nesting_info - Information for nesting-capable IOMMU.
> > + *				user space should check it before using
> > + *				nesting capability.
> > + *
> > + * @size:	size of the whole structure
> > + * @format:	PASID table entry format, the same definition with
> > + *		@format of struct iommu_gpasid_bind_data.
> > + * @features:	supported nesting features.
> > + * @flags:	currently reserved for future extension.
> > + * @data:	vendor specific cap info.
> > + *
> > + * +---------------+--------------------------------------------------=
--+
> > + * | feature       |  Notes                                           =
  |
> > + *
> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> =3D+
> > + * | SYSWIDE_PASID |  Kernel manages PASID in system wide, PASIDs used=
  |
> > + * |               |  in the system should be allocated by host kernel=
  |
> > + * +---------------+--------------------------------------------------=
--+
> > + * | BIND_PGTBL    |  bind page tables to host PASID, the PASID could =
  |
> > + * |               |  either be a host PASID passed in bind request or=
  |
> > + * |               |  default PASIDs (e.g. default PASID of aux-domain=
) |
> > + * +---------------+--------------------------------------------------=
--+
> > + * | CACHE_INVLD   |  mandatory feature for nesting capable IOMMU     =
  |
> > + * +---------------+--------------------------------------------------=
--+
>=20
> This feature description is vague about what CACHE_INVLD does and how to
> use it. If I understand correctly, the presence of this feature means
> that VFIO_IOMMU_NESTING_OP_CACHE_INVLD must be used?
>
> The same kind of clarification could be done for SYSWIDE_PASID and
> BIND_PGTBL too.

For SYSWIDE_PASID and BIND_PGTBL, yes, presence of the feature bit
means must use. So the two are requirements to user space if it wants
to setup nesting. While for CACHE_INVLD, it's kind of availability
here. How about removing CACHE_INVLD as presence of BIND_PGTBL should
indicates support of CACHE_INVLD?

Regards,
Yi Liu

> Stefan