linux-kernel - RE: Plan for /dev/ioasid RFC v2

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Date:   Wed, 9 Jun 2021 09:43:42 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     Jason Gunthorpe <jgg@...dia.com>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Jason Wang <jasowang@...hat.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shenming Lu <lushenming@...wei.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "Kirti Wankhede" <kwankhede@...dia.com>,
        Robin Murphy <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "David Woodhouse" <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: RE: Plan for /dev/ioasid RFC v2

> From: Leon Romanovsky <leon@...nel.org>
> Sent: Wednesday, June 9, 2021 5:02 PM
> 
> On Mon, Jun 07, 2021 at 02:58:18AM +0000, Tian, Kevin wrote:
> > Hi, all,
> 
> <...>
> 
> > (Remaining opens in v1)
> 
> <...>
> 
> > -   Device-centric (Jason) vs. group-centric (David) uAPI. David is not fully
> >     convinced yet. Based on discussion v2 will continue to have ioasid uAPI
> >     being device-centric (but it's fine for vfio to be group-centric). A new
> >     section will be added to elaborate this part;
> 
> <...>
> 
> > (Adopted suggestions)
> 
> <...>
> 
> > -   (Jason) Addition of device label allows per-device capability/format
> >     check before IOASIDs are created. This leads to another major uAPI
> >     change in v2 - specify format info when creating an IOASID (mapping
> >     protocol, nesting, coherent, etc.). User is expected to check per-device
> >     format and then set proper format for IOASID upon to-be-attached
> >     device;
> 
> Sorry for my naive question, I still didn't read all v1 thread and maybe
> the answer is already written, but will ask anyway.
> 
> Doesn't this adopted suggestion to allow device-specific configuration
> actually means that uAPI should be device-centric?
> 
> User already needs to be aware of device, configure it explicitly, maybe
> gracefully clean it later, it looks like not so much left to be group-centric.
> 

Yes, this is what v2 will lean toward. /dev/ioasid reports format info and 
handle IOASID attachment per device. VFIO could still keep its group-
centric uAPI, but in the end it needs bind each device in the group to 
IOASID FD one-by-one. 

Thanks
Kevin