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

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Message-ID: <20210510205632.13ff7308@jacob-builder>
Date:   Mon, 10 May 2021 20:56:32 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.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>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs

Hi Jason,

On Mon, 10 May 2021 20:45:00 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:

> 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.
> 
Sure, we can make the local PASID as default. My point was that the
ioasid_set infrastructure's opaque token can support RID-local allocation
scheme. Anyway, this is a small detail as compared to uAPI.

> 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.
> 
Agreed, the requirements for kernel API should come from uAPI.

> Jason


Thanks,

Jacob