Virtualization - Apr 2022 - [PATCH v9 02/32] virtio: struct virtio_config_ops add callbacks for queue_reset

Performing reset on a queue is divided into four steps:

 1. transport: notify the device to reset the queue
 2. vring:     recycle the buffer submitted
 3. vring:     reset/resize the vring (may re-alloc)
 4. transport: mmap vring to device, and enable the queue

In order to support queue reset, add two callbacks(reset_vq,
enable_reset_vq) in struct virtio_config_ops to implement steps 1 and 4.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 include/linux/virtio_config.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
index 4d107ad31149..d4adcd0e1c57 100644
--- a/include/linux/virtio_config.h
+++ b/include/linux/virtio_config.h
@@ -74,6 +74,16 @@ struct virtio_shm_region {
  * @set_vq_affinity: set the affinity for a virtqueue (optional).
  * @get_vq_affinity: get the affinity for a virtqueue (optional).
  * @get_shm_region: get a shared memory region based on the index.
+ * @reset_vq: reset a queue individually (optional).
+ *	vq: the virtqueue
+ *	Returns 0 on success or error status
+ *	reset_vq will guarantee that the callbacks are disabled and synchronized.
+ *	Except for the callback, the caller should guarantee that the vring is
+ *	not accessed by any functions of virtqueue.
+ * @enable_reset_vq: enable a reset queue
+ *	vq: the virtqueue
+ *	Returns 0 on success or error status
+ *	If reset_vq is set, then enable_reset_vq must also be set.
  */
 typedef void vq_callback_t(struct virtqueue *);
 struct virtio_config_ops {
@@ -100,6 +110,8 @@ struct virtio_config_ops {
 			int index);
 	bool (*get_shm_region)(struct virtio_device *vdev,
 			       struct virtio_shm_region *region, u8 id);
+	int (*reset_vq)(struct virtqueue *vq);
+	int (*enable_reset_vq)(struct virtqueue *vq);
 };
 
 /* If driver didn't advertise the feature, it will never appear. */
-- 
2.31.0

? 2022/4/6 ??11:43, Xuan Zhuo ??:
> Performing reset on a queue is divided into four steps:
>
>   1. transport: notify the device to reset the queue
>   2. vring:     recycle the buffer submitted
>   3. vring:     reset/resize the vring (may re-alloc)
>   4. transport: mmap vring to device, and enable the queue

Nit: it looks to me we'd better say it's an example (since step 3 or 
even 2 is not a must).

>
> In order to support queue reset, add two callbacks(reset_vq,
> enable_reset_vq) in struct virtio_config_ops to implement steps 1 and 4.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> ---
>   include/linux/virtio_config.h | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 4d107ad31149..d4adcd0e1c57 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -74,6 +74,16 @@ struct virtio_shm_region {
>    * @set_vq_affinity: set the affinity for a virtqueue (optional).
>    * @get_vq_affinity: get the affinity for a virtqueue (optional).
>    * @get_shm_region: get a shared memory region based on the index.
> + * @reset_vq: reset a queue individually (optional).
> + *	vq: the virtqueue
> + *	Returns 0 on success or error status
> + *	reset_vq will guarantee that the callbacks are disabled and
synchronized.
> + *	Except for the callback, the caller should guarantee that the vring is

I wonder what's the implications for virtio hardening[1]. In that 
series, we agree to have a synchronize_vqs() config ops to make sure 
callbacks are synchronized.

It uses a global flag and a device wise synchronization mechanism. It 
looks to me we need to switch to

1) per virtqueue flag
2) per virtqueue synchronization

Thanks

> + *	not accessed by any functions of virtqueue.
> + * @enable_reset_vq: enable a reset queue
> + *	vq: the virtqueue
> + *	Returns 0 on success or error status
> + *	If reset_vq is set, then enable_reset_vq must also be set.
>    */
>   typedef void vq_callback_t(struct virtqueue *);
>   struct virtio_config_ops {
> @@ -100,6 +110,8 @@ struct virtio_config_ops {
>   			int index);
>   	bool (*get_shm_region)(struct virtio_device *vdev,
>   			       struct virtio_shm_region *region, u8 id);
> +	int (*reset_vq)(struct virtqueue *vq);
> +	int (*enable_reset_vq)(struct virtqueue *vq);
>   };
>   
>   /* If driver didn't advertise the feature, it will never appear. */