linux-kernel - Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

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Message-ID: <20210510234500.GI1002214@nvidia.com>
Date:   Mon, 10 May 2021 20:45:00 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Auger Eric <eric.auger@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jonathan Corbet <corbet@....net>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs

On Mon, May 10, 2021 at 03:28:54PM -0700, Jacob Pan wrote:

> To satisfy your "give me a PASID for this RID" proposal, can we just use
> the RID's struct device as the token? Also add a type field to explicitly
> indicate global vs per-set(per-RID). i.e.

You've got it backwards, the main behavior should be to allocate PASID
per RID.

The special behavior is to bundle a bunch of PASIDs into a grouping
and then say the PASID number space is shared between all the group
members. 

/dev/ioasid should create and own this grouping either implicitly or
explicitly. Jumping ahead to in-kernel APIs has missed the critical
step of defining the uAPI and all the behaviors together in a
completed RFC proposal.

Jason