Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in
 Userspace
To:     Yongji Xie <xieyongji@bytedance.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Stefano Garzarella <sgarzare@redhat.com>,
        Parav Pandit <parav@nvidia.com>,
        Christoph Hellwig <hch@infradead.org>,
        Christian Brauner <christian.brauner@canonical.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Matthew Wilcox <willy@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jens Axboe <axboe@kernel.dk>, bcrl@kvack.org,
        Jonathan Corbet <corbet@lwn.net>,
        =?UTF-8?Q?Mika_Penttil=c3=a4?= <mika.penttila@nextfour.com>,
        Dan Carpenter <dan.carpenter@oracle.com>, joro@8bytes.org,
        Greg KH <gregkh@linuxfoundation.org>, songmuchun@bytedance.com,
        virtualization <virtualization@lists.linux-foundation.org>,
        netdev@vger.kernel.org, kvm <kvm@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org, iommu@lists.linux-foundation.org,
        linux-kernel <linux-kernel@vger.kernel.org>
References: <20210615141331.407-1-xieyongji@bytedance.com>
 <20210615141331.407-10-xieyongji@bytedance.com>
 <adfb2be9-9ed9-ca37-ac37-4cd00bdff349@redhat.com>
 <CACycT3tAON+-qZev+9EqyL2XbgH5HDspOqNt3ohQLQ8GqVK=EA@mail.gmail.com>
 <1bba439f-ffc8-c20e-e8a4-ac73e890c592@redhat.com>
 <CACycT3uzMJS7vw6MVMOgY4rb=SPfT2srV+8DPdwUVeELEiJgbA@mail.gmail.com>
 <0aeb7cb7-58e5-1a95-d830-68edd7e8ec2e@redhat.com>
 <CACycT3uuooKLNnpPHewGZ=q46Fap2P4XCFirdxxn=FxK+X1ECg@mail.gmail.com>
 <e4cdee72-b6b4-d055-9aac-3beae0e5e3e1@redhat.com>
 <CACycT3u8=_D3hCtJR+d5BgeUQMce6S7c_6P3CVfvWfYhCQeXFA@mail.gmail.com>
 <d2334f66-907c-2e9c-ea4f-f912008e9be8@redhat.com>
 <CACycT3uCSLUDVpQHdrmuxSuoBDg-4n22t+N-Jm2GoNNp9JYB2w@mail.gmail.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <48cab125-093b-2299-ff9c-3de8c7c5ed3d@redhat.com>
Date:   Thu, 24 Jun 2021 16:13:56 +0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0)
 Gecko/20100101 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <CACycT3uCSLUDVpQHdrmuxSuoBDg-4n22t+N-Jm2GoNNp9JYB2w@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Precedence: bulk


在 2021/6/24 下午12:46, Yongji Xie 写道:
>> So we need to deal with both FEATURES_OK and reset, but probably not
>> DRIVER_OK.
>>
> OK, I see. Thanks for the explanation. One more question is how about
> clearing the corresponding status bit in get_status() rather than
> making set_status() fail. Since the spec recommends this way for
> validation which is done in virtio_dev_remove() and
> virtio_finalize_features().
>
> Thanks,
> Yongji
>

I think you can. Or it would be even better that we just don't set the 
bit during set_status().

I just realize that in vdpa_reset() we had:

static inline void vdpa_reset(struct vdpa_device *vdev)
{
         const struct vdpa_config_ops *ops = vdev->config;

         vdev->features_valid = false;
         ops->set_status(vdev, 0);
}

We probably need to add the synchronization here. E.g re-read with a 
timeout.

Thanks