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Date:   Tue, 1 Jun 2021 14:29:56 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Jason Wang <jasowang@redhat.com>
Cc:     "Tian, Kevin" <kevin.tian@intel.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Liu Yi L <yi.l.liu@linux.intel.com>,
        "Alex Williamson (alex.williamson@redhat.com)\"\"" 
        <alex.williamson@redhat.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        LKML <linux-kernel@vger.kernel.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        David Woodhouse <dwmw2@infradead.org>
Subject: Re: [RFC] /dev/ioasid uAPI proposal
Message-ID: <20210601172956.GL1002214@nvidia.com>
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On Tue, Jun 01, 2021 at 02:07:05PM +0800, Jason Wang wrote:

> For the case of 1M, I would like to know what's the use case for a single
> process to handle 1M+ address spaces?

For some scenarios every guest PASID will require a IOASID ID # so
there is a large enough demand that FDs alone are not a good fit.

Further there are global container wide properties that are hard to
carry over to a multi-FD model, like the attachment of devices to the
container at the startup.

> > So this RFC treats fd as a container of address spaces which is each
> > tagged by an IOASID.
> 
> If the container and address space is 1:1 then the container seems useless.

The examples at the bottom of the document show multiple IOASIDs in
the container for a parent/child type relationship

Jason