Re: [PATCH v1 1/1] virtio: Restore semantics of vq->broken in virtqueues

[Michael S. Tsirkin]

On Thu, Jun 30, 2022 at 09:36:46AM +0000, Alexander Atanasov wrote:
> virtio: harden vring IRQ (8b4ec69d7e09) changed the use
> of vq->broken. As result vring_interrupt handles IRQs for
> broken drivers as IRQ_NONE and not IRQ_HANDLED and made impossible
> to initiallize vqs before the driver is ready, i.e. in probe method.
> Balloon driver does this and it can not load because it fails in
> vqs_init with -EIO.
> 
> So instead of changing the original intent ot the flag introduce
> a new flag vq->ready which servers the purpose to check of early IRQs
> and restore the behaviour of the vq->broken flag.
> 
> Signed-off-by: Alexander Atanasov <alexander.atanasov@xxxxxxxxxxxxx>


Does

commit c346dae4f3fbce51bbd4f2ec5e8c6f9b91e93163
Author: Jason Wang <jasowang@xxxxxxxxxx>
Date:   Wed Jun 22 09:29:40 2022 +0800

    virtio: disable notification hardening by default


solve the problem for you?

> ---
>  drivers/virtio/virtio_ring.c  | 20 ++++++++++++++------
>  include/linux/virtio.h        |  2 +-
>  include/linux/virtio_config.h | 10 +++++-----
>  3 files changed, 20 insertions(+), 12 deletions(-)
> 
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> Cc: Halil Pasic <pasic@xxxxxxxxxxxxx>
> Cc: Cornelia Huck <cohuck@xxxxxxxxxx>
> Cc: Vineeth Vijayan <vneethv@xxxxxxxxxxxxx>
> Cc: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx>
> Cc: linux-s390@xxxxxxxxxxxxxxx
> Cc: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> 
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 13a7348cedff..dca3cc774584 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -100,6 +100,9 @@ struct vring_virtqueue {
>  	/* Other side has made a mess, don't try any more. */
>  	bool broken;
>  
> +	/* the queue is ready to handle interrupts  */
> +	bool ready;
> +
>  	/* Host supports indirect buffers */
>  	bool indirect;
>  
> @@ -1688,7 +1691,8 @@ static struct virtqueue *vring_create_virtqueue_packed(
>  	vq->we_own_ring = true;
>  	vq->notify = notify;
>  	vq->weak_barriers = weak_barriers;
> -	vq->broken = true;
> +	vq->broken = false;
> +	vq->ready = false;
>  	vq->last_used_idx = 0;
>  	vq->event_triggered = false;
>  	vq->num_added = 0;
> @@ -2134,7 +2138,10 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
>  		return IRQ_NONE;
>  	}
>  
> -	if (unlikely(vq->broken)) {
> +	if (unlikely(vq->broken))
> +		return IRQ_HANDLED;
> +
> +	if (unlikely(!vq->ready)) {
>  		dev_warn_once(&vq->vq.vdev->dev,
>  			      "virtio vring IRQ raised before DRIVER_OK");
>  		return IRQ_NONE;
> @@ -2180,7 +2187,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
>  	vq->we_own_ring = false;
>  	vq->notify = notify;
>  	vq->weak_barriers = weak_barriers;
> -	vq->broken = true;
> +	vq->broken = false;
> +	vq->ready = false;
>  	vq->last_used_idx = 0;
>  	vq->event_triggered = false;
>  	vq->num_added = 0;
> @@ -2405,7 +2413,7 @@ EXPORT_SYMBOL_GPL(virtio_break_device);
>   * (probing and restoring). This function should only be called by the
>   * core, not directly by the driver.
>   */
> -void __virtio_unbreak_device(struct virtio_device *dev)
> +void __virtio_device_ready(struct virtio_device *dev)
>  {
>  	struct virtqueue *_vq;
>  
> @@ -2414,11 +2422,11 @@ void __virtio_unbreak_device(struct virtio_device *dev)
>  		struct vring_virtqueue *vq = to_vvq(_vq);
>  
>  		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */
> -		WRITE_ONCE(vq->broken, false);
> +		WRITE_ONCE(vq->ready, true);
>  	}
>  	spin_unlock(&dev->vqs_list_lock);
>  }
> -EXPORT_SYMBOL_GPL(__virtio_unbreak_device);
> +EXPORT_SYMBOL_GPL(__virtio_device_ready);
>  
>  dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
>  {
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index d8fdf170637c..538c5959949a 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -131,7 +131,7 @@ void unregister_virtio_device(struct virtio_device *dev);
>  bool is_virtio_device(struct device *dev);
>  
>  void virtio_break_device(struct virtio_device *dev);
> -void __virtio_unbreak_device(struct virtio_device *dev);
> +void __virtio_device_ready(struct virtio_device *dev);
>  
>  void virtio_config_changed(struct virtio_device *dev);
>  #ifdef CONFIG_PM_SLEEP
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 49c7c32815f1..35cf1b26e05a 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -259,21 +259,21 @@ void virtio_device_ready(struct virtio_device *dev)
>  
>  	/*
>  	 * The virtio_synchronize_cbs() makes sure vring_interrupt()
> -	 * will see the driver specific setup if it sees vq->broken
> +	 * will see the driver specific setup if it sees vq->ready
>  	 * as false (even if the notifications come before DRIVER_OK).
>  	 */
>  	virtio_synchronize_cbs(dev);
> -	__virtio_unbreak_device(dev);
> +	__virtio_device_ready(dev);
>  	/*
> -	 * The transport should ensure the visibility of vq->broken
> +	 * The transport should ensure the visibility of vq->ready
>  	 * before setting DRIVER_OK. See the comments for the transport
>  	 * specific set_status() method.
>  	 *
>  	 * A well behaved device will only notify a virtqueue after
>  	 * DRIVER_OK, this means the device should "see" the coherenct
> -	 * memory write that set vq->broken as false which is done by
> +	 * memory write that set vq->ready as true which is done by
>  	 * the driver when it sees DRIVER_OK, then the following
> -	 * driver's vring_interrupt() will see vq->broken as false so
> +	 * driver's vring_interrupt() will see vq->true as true so
>  	 * we won't lose any notification.
>  	 */
>  	dev->config->set_status(dev, status | VIRTIO_CONFIG_S_DRIVER_OK);
> -- 
> 2.25.1