linux-kernel - RE: [RFC 14/20] iommu/iommufd: Add iommufd_device_[de]attach

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Date:   Wed, 22 Sep 2021 14:16:27 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "lkml@...ux.net" <lkml@...ux.net>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "corbet@....net" <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>
Subject: RE: [RFC 14/20] iommu/iommufd: Add iommufd_device_[de]attach_ioasid()

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Wednesday, September 22, 2021 8:57 PM
> 
> On Wed, Sep 22, 2021 at 03:53:52AM +0000, Tian, Kevin wrote:
> 
> > Actually this was one open we closed in previous design proposal, but
> > looks you have a different thought now.
> >
> > vfio maintains one ioas per container. Devices in the container
> > can be attached to different domains (e.g. due to snoop format). Every
> > time when the ioas is updated, every attached domain is updated
> > in accordance.
> >
> > You recommended one-ioas-one-domain model instead, i.e. any device
> > with a format incompatible with the one currently used in ioas has to
> > be attached to a new ioas, even if the two ioas's have the same mapping.
> > This leads to compatibility check at attaching time.
> >
> > Now you want returning back to the vfio model?
> 
> Oh, I thought we circled back again.. If we are all OK with one ioas
> one domain then great.

yes, at least I haven't seen a blocking issue with this assumption. Later
when converting vfio type1 into a shim, it could create multiple ioas's
if container would have a list of domains before the shim.

> 
> > > If think sis taking in the iommfd_device then there isn't a logical
> > > place to signal the PCIness
> >
> > can you elaborate?
> 
> I mean just drop it and document it.
> 

got you