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Subject: Re: [RFC] /dev/ioasid uAPI proposal
To:     Shenming Lu <lushenming@huawei.com>,
        Liu Yi L <yi.l.liu@linux.intel.com>
Cc:     yi.l.liu@intel.com, "Tian, Kevin" <kevin.tian@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Jason Gunthorpe <jgg@nvidia.com>,
        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>,
        Zenghui Yu <yuzenghui@huawei.com>,
        "wanghaibin.wang@huawei.com" <wanghaibin.wang@huawei.com>
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <e95add68-7556-f8a3-695b-40389742a682@redhat.com>
Date:   Tue, 1 Jun 2021 13:10:30 +0800
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在 2021/6/1 下午12:27, Shenming Lu 写道:
> On 2021/6/1 10:36, Jason Wang wrote:
>> åœ¨ 2021/5/31 ä¸‹å�ˆ4:41, Liu Yi L å†™é�“:
>>>> I guess VFIO_ATTACH_IOASID will fail if the underlayer doesn't support
>>>> hardware nesting. Or is there way to detect the capability before?
>>> I think it could fail in the IOASID_CREATE_NESTING. If the gpa_ioasid
>>> is not able to support nesting, then should fail it.
>>>
>>>> I think GET_INFO only works after the ATTACH.
>>> yes. After attaching to gpa_ioasid, userspace could GET_INFO on the
>>> gpa_ioasid and check if nesting is supported or not. right?
>>
>> Some more questions:
>>
>> 1) Is the handle returned by IOASID_ALLOC an fd?
>> 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?
> It seems that the return value from IOASID_ALLOC is an IOASID number in the
> ioasid_data struct, then when calling GET_INFO, we should convey this IOASID
> number to get the associated I/O address space attributes (depend on the
> physical IOMMU, which could be discovered when attaching a device to the
> IOASID fd or number), right?


Right, but the question is why need such indirection? Unless there's a 
case that you need to create multiple IOASIDs per ioasid fd. It's more 
simpler to attach the metadata into the ioasid fd itself.

Thanks


>
> Thanks,
> Shenming
>