linux-kernel - Re: [RFC PATCH] virtio: do not reset stateful devices on resume

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Date:   Thu, 16 Dec 2021 10:55:25 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Mikhail Golubev <mgo@...nsynergy.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Mikhail Golubev <Mikhail.Golubev@...nsynergy.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Anton Yakovlev <Anton.Yakovlev@...nsynergy.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [RFC PATCH] virtio: do not reset stateful devices on resume

On Thu, Dec 16, 2021 at 1:27 AM Mikhail Golubev <mgo@...nsynergy.com> wrote:
>
> The 12/14/2021 18:26, Michael S. Tsirkin wrote:
> > On Tue, Dec 14, 2021 at 05:33:05PM +0100, Mikhail Golubev wrote:
> > > From: Anton Yakovlev <Anton.Yakovlev@...nsynergy.com>
> > >
> > > We assume that stateful devices can maintain their state while
> > > suspended. And for this reason they don't have a freeze callback. If
> > > such a device is reset during resume, the device state/context will be
> > > lost on the device side. And the virtual device will stop working.
> > >
> > > Signed-off-by: Anton Yakovlev <Anton.Yakovlev@...nsynergy.com>
> > > Signed-off-by: Mikhail Golubev <mikhail.golubev@...nsynergy.com>
> >
> > A bit more specific? Which configs does this patch fix?
>
> We had encountered an issue related to 'stateful' GPU 3d (virglrenderer) and
> video (gstreamer) devices.

Adding Gerd and Stefan.

I wonder if we suffer from a similar issue with virtio-fs.

Thanks

>
> BR,
> Mikhail
>
> >
> > > ---
> > >  drivers/virtio/virtio.c | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > >
> > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> > > index 236081afe9a2..defa15b56eb8 100644
> > > --- a/drivers/virtio/virtio.c
> > > +++ b/drivers/virtio/virtio.c
> > > @@ -472,6 +472,13 @@ int virtio_device_restore(struct virtio_device *dev)
> > >     struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
> > >     int ret;
> > >
> > > +   /* Short path for stateful devices. Here we assume that if the device
> > > +    * does not have a freeze callback, its state was not changed when
> > > +    * suspended.
> > > +    */
> > > +   if (drv && !drv->freeze)
> > > +           goto on_config_enable;
> > > +
> > >     /* We always start by resetting the device, in case a previous
> > >      * driver messed it up. */
> > >     dev->config->reset(dev);
> > > @@ -503,6 +510,7 @@ int virtio_device_restore(struct virtio_device *dev)
> > >     /* Finally, tell the device we're all set */
> > >     virtio_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
> > >
> > > +on_config_enable:
> > >     virtio_config_enable(dev);
> > >
> > >     return 0;
> > > --
> > > 2.34.1
> > >
> > >
> > > --
> >
>
> --
>