linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Date:   Tue, 1 Jun 2021 12:27:51 +0800
From:   Shenming Lu <lushenming@...wei.com>
To:     Jason Wang <jasowang@...hat.com>,
        Liu Yi L <yi.l.liu@...ux.intel.com>
CC:     <yi.l.liu@...el.com>, "Tian, Kevin" <kevin.tian@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        "Jason Gunthorpe" <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        "David Woodhouse" <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Alex Williamson (alex.williamson@...hat.com)\"" 
        <alex.williamson@...hat.com>, Eric Auger <eric.auger@...hat.com>,
        "Jonathan Corbet" <corbet@....net>,
        Zenghui Yu <yuzenghui@...wei.com>,
        "wanghaibin.wang@...wei.com" <wanghaibin.wang@...wei.com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

On 2021/6/1 10:36, Jason Wang wrote:
> 
> 在 2021/5/31 下午4:41, Liu Yi L 写道:
>>> 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?

Thanks,
Shenming