linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Date:   Tue, 1 Jun 2021 14:29:56 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Liu Yi L <yi.l.liu@...ux.intel.com>,
        "Alex Williamson (alex.williamson@...hat.com)\"\"" 
        <alex.williamson@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

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