RE: [PATCH v3 02/14] iommu: Report domain nesting info

[Liu, Yi L]

Hi Stefan,

> From: Stefan Hajnoczi <stefanha@xxxxxxxxx>
> 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