linux-kernel - RE: [PATCH v1 2/8] iommu: Introduce a new iommu_group_replace

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Date:   Wed, 8 Feb 2023 04:25:58 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Nicolin Chen <nicolinc@...dia.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: RE: [PATCH v1 2/8] iommu: Introduce a new
 iommu_group_replace_domain() API

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Tuesday, February 7, 2023 8:23 PM
> 
> On Tue, Feb 07, 2023 at 12:32:50AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@...dia.com>
> > > Sent: Monday, February 6, 2023 9:25 PM
> > >
> > > On Mon, Feb 06, 2023 at 06:57:35AM +0000, Tian, Kevin wrote:
> > > > > From: Jason Gunthorpe <jgg@...dia.com>
> > > > > Sent: Friday, February 3, 2023 11:03 PM
> > > > >
> > > > > On Fri, Feb 03, 2023 at 08:26:44AM +0000, Tian, Kevin wrote:
> > > > > > > From: Nicolin Chen <nicolinc@...dia.com>
> > > > > > > Sent: Thursday, February 2, 2023 3:05 PM
> > > > > > >
> > > > > > > All drivers are already required to support changing between
> active
> > > > > > > UNMANAGED domains when using their attach_dev ops.
> > > > > >
> > > > > > All drivers which don't have *broken* UNMANAGED domain?
> > > > >
> > > > > No, all drivers.. It has always been used by VFIO.
> > > >
> > > > existing iommu_attach_group() doesn't support changing between
> > > > two UNMANAGED domains. only from default->unmanaged or
> > > > blocking->unmanaged.
> > >
> > > Yes, but before we added the blocking domains VFIO was changing
> > > between unmanaged domains. Blocking domains are so new that no
> driver
> > > could have suddenly started to depend on this.
> >
> > In legacy VFIO unmanaged domain was 1:1 associated with vfio
> > container. I didn't say how a group can switch between two
> > containers w/o going through transition to/from the default
> > domain, i.e. detach from 1st container and then attach to the 2nd.
> 
> Yes, in the past we went through the default domain which is basically
> another unmanaged domain type. So unmanaged -> unmanaged is OK.
> 

it's right in concept but confusing in current context whether DMA
domain still has its own type. That's why I replied earlier the statement
makes more sense after your patch which cleans up the domain type
is merged.