Re: [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace

From: Jason Wang <jasowang@redhat.com>
To: Yongji Xie <xieyongji@bytedance.com>
Cc: kvm <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>,
	virtualization <virtualization@lists.linux-foundation.org>,
	"Christian Brauner" <christian.brauner@canonical.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	joro@8bytes.org, "Matthew Wilcox" <willy@infradead.org>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Dan Carpenter" <dan.carpenter@oracle.com>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	songmuchun@bytedance.com, "Jens Axboe" <axboe@kernel.dk>,
	"Greg KH" <gregkh@linuxfoundation.org>,
	"Randy Dunlap" <rdunlap@infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	iommu@lists.linux-foundation.org, bcrl@kvack.org,
	netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	"Mika Penttilä" <mika.penttila@nextfour.com>
Subject: Re: [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace
Date: Thu, 24 Jun 2021 16:13:56 +0800	[thread overview]
Message-ID: <48cab125-093b-2299-ff9c-3de8c7c5ed3d@redhat.com> (raw)
In-Reply-To: <CACycT3uCSLUDVpQHdrmuxSuoBDg-4n22t+N-Jm2GoNNp9JYB2w@mail.gmail.com>

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

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