linux-kernel - Re: [PATCH v3 02/14] iommu: Report domain nesting info

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Date:   Mon, 29 Jun 2020 10:24:48 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Liu Yi L <yi.l.liu@...el.com>
Cc:     alex.williamson@...hat.com, eric.auger@...hat.com,
        baolu.lu@...ux.intel.com, joro@...tes.org, kevin.tian@...el.com,
        jacob.jun.pan@...ux.intel.com, ashok.raj@...el.com,
        jun.j.tian@...el.com, yi.y.sun@...el.com, jean-philippe@...aro.org,
        peterx@...hat.com, hao.wu@...el.com,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 02/14] iommu: Report domain nesting info

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.

Stefan

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