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Date:   Thu, 24 Jun 2021 14:37:31 +1000
From:   David Gibson <david@gibson.dropbear.id.au>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Alex Williamson <alex.williamson@redhat.com>,
        Joerg Roedel <joro@8bytes.org>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Jason Wang <jasowang@redhat.com>,
        "parav@mellanox.com" <parav@mellanox.com>,
        "Enrico Weigelt, metux IT consult" <lkml@metux.net>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Shenming Lu <lushenming@huawei.com>,
        Eric Auger <eric.auger@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
        "Jiang, Dave" <dave.jiang@intel.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Kirti Wankhede <kwankhede@nvidia.com>,
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        David Woodhouse <dwmw2@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Lu Baolu <baolu.lu@linux.intel.com>
Subject: Re: Plan for /dev/ioasid RFC v2
Message-ID: <YNQMC4GcV3gxjerb@yekko>
References: <MWHPR11MB188699D0B9C10EB51686C4138C389@MWHPR11MB1886.namprd11.prod.outlook.com>
 <YMCy48Xnt/aphfh3@8bytes.org>
 <20210609123919.GA1002214@nvidia.com>
 <YMDC8tOMvw4FtSek@8bytes.org>
 <20210609150009.GE1002214@nvidia.com>
 <YMDjfmJKUDSrbZbo@8bytes.org>
 <20210609101532.452851eb.alex.williamson@redhat.com>
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 <20210617230438.GZ1002214@nvidia.com>
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On Thu, Jun 17, 2021 at 08:04:38PM -0300, Jason Gunthorpe wrote:
> On Thu, Jun 17, 2021 at 03:02:33PM +1000, David Gibson wrote:
>=20
> > In other words, do we really have use cases where we need to identify
> > different devices IDs, even though we know they're not isolated.
>=20
> I think when PASID is added in and all the complexity that brings, it
> does become more important, yes.
>=20
> At the minimum we should scope the complexity.
>=20
> I'm not convinced it is so complicated, really it is just a single bit
> of information toward userspace: 'all devices in this group must use
> the same IOASID'

Um.. no?  You could have devA and devB sharing a RID, but then also
sharing a group but not a RID with devC because of different isolation
issues.  So you now have (at least) two levels of group structure to
expose somehow.

>=20
> Something like qemu consumes this bit and creates the pci/pcie bridge
> to model this to the guest and so on.
>=20
> Something like dpdk just doesn't care (same as today).
>=20
> Jason
>=20

--=20
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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