Re: [PATCH RESEND] virtio_console: read size from config space during device init

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Feb 23, 2026 at 06:37:02PM +0100, Filip Hejsek wrote:
> Previously, the size was only read upon receiving the config interrupt.
> This interrupt is sent when the size changes. However, we also need to
> read the initial size.
> 
> Also make sure to only read the size from config if F_SIZE is enabled.
> 
> Fixes: 9778829cffd4 ("virtio: console: Store each console's size in the console structure")
> Signed-off-by: Filip Hejsek <filip.hejsek@gmail.com>
> ---
> This is a resend of [1], which hasn't received any response.
> 
> I found this bug while developing patches for QEMU that add virtio
> console resize support. If you want to test this, you can get my QEMU
> patches from [2]. You will need to disable multiport
> using `-device virtio-serial,max_ports=1`.
> 
> [1]: https://lore.kernel.org/all/20251224-virtio-console-fix-v1-1-69d0349692dc@gmail.com/
> [2]: https://lore.kernel.org/all/20250921-console-resize-v5-0-89e3c6727060@gmail.com/
> 
> I'll also repeat my questions from the previous submission here. These are
> things that confused me when I was trying to understand the surrounding code,
> but should in no way prevent merging this patch.
> 
>   - Why does use_multiport use __virtio_test_bit instead of
>     virtio_has_feature?
> 
>   - The VIRTIO_CONSOLE_RESIZE handler sets irq_requested to 1, which I
>     think makes no sense?
> ---
>  drivers/char/virtio_console.c | 52 ++++++++++++++++++++++++++-----------------
>  1 file changed, 31 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 088182e54d..c355f6d392 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -1771,32 +1771,40 @@ static void config_intr(struct virtio_device *vdev)
>  		schedule_work(&portdev->config_work);
>  }
>  
> -static void config_work_handler(struct work_struct *work)
> +static void update_size_from_config(struct ports_device *portdev)
>  {
> -	struct ports_device *portdev;
> +	struct virtio_device *vdev;
> +	struct port *port;
> +	u16 rows, cols;
>  
> -	portdev = container_of(work, struct ports_device, config_work);
> -	if (!use_multiport(portdev)) {
> -		struct virtio_device *vdev;
> -		struct port *port;
> -		u16 rows, cols;
> +	vdev = portdev->vdev;
>  
> -		vdev = portdev->vdev;
> -		virtio_cread(vdev, struct virtio_console_config, cols, &cols);
> -		virtio_cread(vdev, struct virtio_console_config, rows, &rows);
> +	/*
> +	 * We'll use this way of resizing only for legacy support.
> +	 * For multiport devices, use control messages to indicate
> +	 * console size changes so that it can be done per-port.
> +	 *
> +	 * Don't test F_SIZE at all if we're rproc: not a valid feature.
> +	 */
> +	if (is_rproc_serial(vdev) ||

Wait a second. Why is there this rproc test here?
Was not in the original code and commit log says nothing about it.


> +	    use_multiport(portdev) ||
> +	    !virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE))
> +		return;
>  
> -		port = find_port_by_id(portdev, 0);
> -		set_console_size(port, rows, cols);
> +	virtio_cread(vdev, struct virtio_console_config, cols, &cols);
> +	virtio_cread(vdev, struct virtio_console_config, rows, &rows);
>  
> -		/*
> -		 * We'll use this way of resizing only for legacy
> -		 * support.  For newer userspace
> -		 * (VIRTIO_CONSOLE_F_MULTPORT+), use control messages
> -		 * to indicate console size changes so that it can be
> -		 * done per-port.
> -		 */
> -		resize_console(port);
> -	}
> +	port = find_port_by_id(portdev, 0);
> +	set_console_size(port, rows, cols);
> +	resize_console(port);
> +}
> +
> +static void config_work_handler(struct work_struct *work)
> +{
> +	struct ports_device *portdev;
> +
> +	portdev = container_of(work, struct ports_device, config_work);
> +	update_size_from_config(portdev);
>  }
>  
>  static int init_vqs(struct ports_device *portdev)
> @@ -2054,6 +2062,8 @@ static int virtcons_probe(struct virtio_device *vdev)
>  	__send_control_msg(portdev, VIRTIO_CONSOLE_BAD_ID,
>  			   VIRTIO_CONSOLE_DEVICE_READY, 1);
>  
> +	update_size_from_config(portdev);
> +
>  	return 0;
>  
>  free_chrdev:
> 
> ---
> base-commit: b927546677c876e26eba308550207c2ddf812a43
> change-id: 20251224-virtio-console-fix-3d46980ef569
> 
> Best regards,
> -- 
> Filip Hejsek <filip.hejsek@gmail.com>