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

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Date:   Wed, 28 Apr 2021 10:49:03 +1000
From:   David Gibson <david@...son.dropbear.id.au>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Auger Eric <eric.auger@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        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>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Alexey Kardashevskiy <aik@...abs.ru>
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs

On Tue, Apr 27, 2021 at 01:39:54PM -0300, Jason Gunthorpe wrote:
> On Tue, Apr 27, 2021 at 03:11:25PM +1000, David Gibson wrote:
> 
> > > So your proposal sort of moves the entire container/group/domain 
> > > managment into /dev/ioasid and then leaves vfio only provide device
> > > specific uAPI. An ioasid represents a page table (address space), thus 
> > > is equivalent to the scope of VFIO container.
> > 
> > Right.  I don't really know how /dev/iosasid is supposed to work, and
> > so far I don't see how it conceptually differs from a container.  What
> > is it adding?
> 
> There are three motivating topics:
>  1) /dev/vfio/vfio is only usable by VFIO and we have many interesting
>     use cases now where we need the same thing usable outside VFIO
>  2) /dev/vfio/vfio does not support modern stuff like PASID and
>     updating to support that is going to be a big change, like adding
>     multiple IOASIDs so they can be modeled as as a tree inside a
>     single FD
>  3) I understand there is some desire to revise the uAPI here a bit,
>     ie Alex mentioned the poor mapping performance.
> 
> I would say it is not conceptually different from what VFIO calls a
> container, it is just a different uAPI with the goal to be cross
> subsystem.

Ok, that makes sense.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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