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Date:   Thu, 3 Jun 2021 09:46:07 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     David Gibson <david@gibson.dropbear.id.au>
Cc:     "Tian, Kevin" <kevin.tian@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        David Woodhouse <dwmw2@infradead.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "Alex Williamson (alex.williamson@redhat.com)" 
        <alex.williamson@redhat.com>, Jason Wang <jasowang@redhat.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>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Kirti Wankhede <kwankhede@nvidia.com>,
        Robin Murphy <robin.murphy@arm.com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal
Message-ID: <20210603124607.GV1002214@nvidia.com>
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On Thu, Jun 03, 2021 at 04:26:08PM +1000, David Gibson wrote:

> > There are global properties in the /dev/iommu FD, like what devices
> > are part of it, that are important for group security operations. This
> > becomes confused if it is split to many FDs.
> 
> I'm still not seeing those.  I'm really not seeing any well-defined
> meaning to devices being attached to the fd, but not to a particular
> IOAS.

Kevin can you add a section on how group security would have to work
to the RFC? This is the idea you can't attach a device to an IOASID
unless all devices in the IOMMU group are joined to the /dev/iommu FD.

The basic statement is that userspace must present the entire group
membership to /dev/iommu to prove that it has the security right to
manipulate their DMA translation.

It is the device centric analog to what the group FD is doing for
security.

Jason