linux-kernel - Re: Re: [PATCH v8 09/10] vduse: Introduce VDUSE

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Message-ID: <CACycT3tS=10kcUCNGYm=dUZsK+vrHzDvB3FSwAzuJCu3t+QuUQ@mail.gmail.com>
Date:   Thu, 24 Jun 2021 17:16:39 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Dan Carpenter <dan.carpenter@...cle.com>, joro@...tes.org,
        Greg KH <gregkh@...uxfoundation.org>, songmuchun@...edance.com,
        virtualization <virtualization@...ts.linux-foundation.org>,
        netdev@...r.kernel.org, kvm <kvm@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace

On Thu, Jun 24, 2021 at 4:14 PM Jason Wang <jasowang@...hat.com> wrote:
>
>
> 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().
>

Yes, that's what I mean.

> 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.
>

Looks like the timeout is already in set_status(). Do we really need a
duplicated one here? And how to handle failure? Adding a return value
to virtio_config_ops->reset() and passing the error to the upper
layer?

Thanks,
Yongji