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Subject: Re: [RFC] /dev/ioasid uAPI proposal
To:     Lu Baolu <baolu.lu@linux.intel.com>,
        Liu Yi L <yi.l.liu@linux.intel.com>
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        Jason Gunthorpe <jgg@nvidia.com>,
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        "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>
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <429d9c2f-3597-eb29-7764-fad3ec9a934f@redhat.com>
Date:   Tue, 1 Jun 2021 13:29:39 +0800
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在 2021/6/1 下午1:23, Lu Baolu 写道:
> Hi Jason W,
>
> On 6/1/21 1:08 PM, Jason Wang wrote:
>>>> 2) If yes, what's the reason for not simply use the fd opened from
>>>> /dev/ioas. (This is the question that is not answered) and what 
>>>> happens
>>>> if we call GET_INFO for the ioasid_fd?
>>>> 3) If not, how GET_INFO work?
>>> oh, missed this question in prior reply. Personally, no special reason
>>> yet. But using ID may give us opportunity to customize the management
>>> of the handle. For one, better lookup efficiency by using xarray to
>>> store the allocated IDs. For two, could categorize the allocated IDs
>>> (parent or nested). GET_INFO just works with an input FD and an ID.
>>
>>
>> I'm not sure I get this, for nesting cases you can still make the 
>> child an fd.
>>
>> And a question still, under what case we need to create multiple 
>> ioasids on a single ioasid fd?
>
> One possible situation where multiple IOASIDs per FD could be used is
> that devices with different underlying IOMMU capabilities are sharing a
> single FD. In this case, only devices with consistent underlying IOMMU
> capabilities could be put in an IOASID and multiple IOASIDs per FD could
> be applied.
>
> Though, I still not sure about "multiple IOASID per-FD" vs "multiple
> IOASID FDs" for such case.


Right, that's exactly my question. The latter seems much more easier to 
be understood and implemented.

Thanks


>
> Best regards,
> baolu
>