linux-kernel - Re: Plan for /dev/ioasid RFC v2

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Date:   Thu, 24 Jun 2021 08:56:31 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     Joerg Roedel <joro@...tes.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Jason Wang <jasowang@...hat.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shenming Lu <lushenming@...wei.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Robin Murphy <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        David Woodhouse <dwmw2@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: Re: Plan for /dev/ioasid RFC v2

On Thu, Jun 24, 2021 at 02:29:29PM +1000, David Gibson wrote:

> But as I keep saying, some forms of grouping (and DMA aliasing as Alex
> mentioned) mean that changing the domain of one device can change the
> domain of another device, unavoidably.  It may be rare with modern
> hardware, but we still can't ignore the case.
> 
> Which means you can't DMA block until everything in the group is
> managed by a vfio-like driver.

We just need the same restriction as today, the group fd will attach a
domain under quite a wide range of conditions, and we can copy that.

IIRC is not a requirement today that every device in the group have a
vfio driver bound to it?

Jason