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Subject: Re: [RFC] /dev/ioasid uAPI proposal
To:     Jason Gunthorpe <jgg@nvidia.com>,
        "Tian, Kevin" <kevin.tian@intel.com>
Cc:     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>, 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>,
        David Gibson <david@gibson.dropbear.id.au>,
        Kirti Wankhede <kwankhede@nvidia.com>,
        Robin Murphy <robin.murphy@arm.com>
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <1a3b4cf2-f511-640b-6c8c-a85f94a9536d@redhat.com>
Date:   Wed, 2 Jun 2021 16:52:02 +0800
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?? 2021/6/2 ????4:28, Jason Gunthorpe д??:
>> I summarized five opens here, about:
>>
>> 1)  Finalizing the name to replace /dev/ioasid;
>> 2)  Whether one device is allowed to bind to multiple IOASID fd's;
>> 3)  Carry device information in invalidation/fault reporting uAPI;
>> 4)  What should/could be specified when allocating an IOASID;
>> 5)  The protocol between vfio group and kvm;
>>
>> For 1), two alternative names are mentioned: /dev/iommu and
>> /dev/ioas. I don't have a strong preference and would like to hear
>> votes from all stakeholders. /dev/iommu is slightly better imho for
>> two reasons. First, per AMD's presentation in last KVM forum they
>> implement vIOMMU in hardware thus need to support user-managed
>> domains. An iommu uAPI notation might make more sense moving
>> forward. Second, it makes later uAPI naming easier as 'IOASID' can
>> be always put as an object, e.g. IOMMU_ALLOC_IOASID instead of
>> IOASID_ALLOC_IOASID.:)
> I think two years ago I suggested /dev/iommu and it didn't go very far
> at the time.


It looks to me using "/dev/iommu" excludes the possibility of 
implementing IOASID in a device specific way (e.g through the 
co-operation with device MMU + platform IOMMU)?

What's more, ATS spec doesn't forbid the device #PF to be reported via a 
device specific way.

Thanks


> We've also talked about this as /dev/sva for a while and
> now /dev/ioasid
>
> I think /dev/iommu is fine, and call the things inside them IOAS
> objects.
>
> Then we don't have naming aliasing with kernel constructs.
>