Re: [PATCH 3/4] virtio: Protect vqs list access

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

On Sat, Jul 17, 2021 at 10:42:57AM +0300, Parav Pandit wrote:
> VQs may be accessed to mark the device broken while they are
> created/destroyed. Hence protect the access to the vqs list.
> 
> Fixes: e2dcdfe95c0b ("virtio: virtio_break_device() to mark all virtqueues broken.")
> Signed-off-by: Parav Pandit <parav@nvidia.com>
> ---
>  drivers/virtio/virtio.c      | 1 +
>  drivers/virtio/virtio_ring.c | 8 ++++++++
>  include/linux/virtio.h       | 1 +
>  3 files changed, 10 insertions(+)
> 
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index 4b15c00c0a0a..a0d81e35ec4b 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -355,6 +355,7 @@ int register_virtio_device(struct virtio_device *dev)
>  	virtio_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE);
>  
>  	INIT_LIST_HEAD(&dev->vqs);
> +	rwlock_init(&dev->vqs_list_lock);
>  
>  	/*
>  	 * device_add() causes the bus infrastructure to look for a matching

Let's just use a simple spinlock. I don't think we are worried about
scaling the breaking of devices to multiple CPUs.

> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index d2e1a7a21171..66a91dec39d9 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1755,7 +1755,9 @@ static struct virtqueue *vring_create_virtqueue_packed(
>  			cpu_to_le16(vq->packed.event_flags_shadow);
>  	}
>  
> +	write_lock(&vdev->vqs_list_lock);
>  	list_add_tail(&vq->vq.list, &vdev->vqs);
> +	write_unlock(&vdev->vqs_list_lock);
>  	return &vq->vq;
>  
>  err_desc_extra:
> @@ -2229,7 +2231,9 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
>  	memset(vq->split.desc_state, 0, vring.num *
>  			sizeof(struct vring_desc_state_split));
>  
> +	write_lock(&vdev->vqs_list_lock);
>  	list_add_tail(&vq->vq.list, &vdev->vqs);
> +	write_unlock(&vdev->vqs_list_lock);
>  	return &vq->vq;
>  
>  err_extra:
> @@ -2291,7 +2295,9 @@ void vring_del_virtqueue(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
> +	write_lock(&vq->vq.vdev->vqs_list_lock);
>  	list_del(&_vq->list);
> +	write_unlock(&vq->vq.vdev->vqs_list_lock);
>  
>  	if (vq->we_own_ring) {
>  		if (vq->packed_ring) {
> @@ -2386,12 +2392,14 @@ void virtio_break_device(struct virtio_device *dev)
>  {
>  	struct virtqueue *_vq;
>  
> +	read_lock(&dev->vqs_list_lock);
>  	list_for_each_entry(_vq, &dev->vqs, list) {
>  		struct vring_virtqueue *vq = to_vvq(_vq);
>  
>  		/* Pairs with READ_ONCE() in virtqueue_is_broken(). */
>  		smp_store_release(&vq->broken, true);
>  	}
> +	read_unlock(&dev->vqs_list_lock);
>  }
>  EXPORT_SYMBOL_GPL(virtio_break_device);
>  
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index b1894e0323fa..1cf77d480ef3 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -115,6 +115,7 @@ struct virtio_device {
>  	const struct virtio_config_ops *config;
>  	const struct vringh_config_ops *vringh_config;
>  	struct list_head vqs;
> +	rwlock_t vqs_list_lock;
>  	u64 features;
>  	void *priv;
>  };
> -- 
> 2.27.0

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