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

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Date:   Thu, 22 Apr 2021 20:55:05 +0800
From:   Liu Yi L <yi.l.liu@...ux.intel.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     yi.l.liu@...el.com, Jason Gunthorpe <jgg@...dia.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Li Zefan <lizefan@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "Wu, Hao" <hao.wu@...el.com>, David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and
 allocation APIs

On Wed, 21 Apr 2021 13:33:12 -0600, Alex Williamson wrote:

> On Wed, 21 Apr 2021 14:52:03 -0300
> Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > On Wed, Apr 21, 2021 at 10:54:51AM -0600, Alex Williamson wrote:
> >   
> > > That's essentially replacing vfio-core, where I think we're more    
> > 
> > I am only talking about /dev/vfio here which is basically the IOMMU
> > interface part.
> > 
> > I still expect that VFIO_GROUP_SET_CONTAINER will be used to connect
> > /dev/{ioasid,vfio} to the VFIO group and all the group and device
> > logic stays inside VFIO.  
> 
> But that group and device logic is also tied to the container, where
> the IOMMU backend is the interchangeable thing that provides the IOMMU
> manipulation for that container.  If you're using
> VFIO_GROUP_SET_CONTAINER to associate a group to a /dev/ioasid, then
> you're really either taking that group outside of vfio or you're
> re-implementing group management in /dev/ioasid.  I'd expect the
> transition point at VFIO_SET_IOMMU.

per my understanding, transiting at the VFIO_SET_IOMMU point makes more
sense as VFIO can still have the group and device logic, which is the key
concept of group granularity isolation for userspace direct access.

-- 
Regards,
Yi Liu