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SubjectRE: [PATCH v3 02/14] iommu: Report domain nesting info
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Hi Stefan,

> From: Stefan Hajnoczi <stefanha@gmail.com>
> Sent: Monday, June 29, 2020 5:25 PM
>
> 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 |
> > + *
> +===============+===================================================
> =+
> > + * | 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 |
> > + * +---------------+----------------------------------------------------+
>
> 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

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