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

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Message-ID: <20211214182611-mutt-send-email-mst@kernel.org>
Date:   Tue, 14 Dec 2021 18:26:39 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Mikhail Golubev <Mikhail.Golubev@...nsynergy.com>
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Anton Yakovlev <Anton.Yakovlev@...nsynergy.com>
Subject: Re: [RFC PATCH] virtio: do not reset stateful devices on resume

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?

> ---
>  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
> 
> 
> --