RE: [PATCH v4] vhost: add new `rte_vhost_vring_call_nonblock` API

["Xia, Chenbo" <chenbo.xia@intel.com>]

> -----Original Message-----
> From: Liu, Changpeng <changpeng.liu@intel.com>
> Sent: Monday, October 17, 2022 3:48 PM
> To: dev@dpdk.org
> Cc: Liu, Changpeng <changpeng.liu@intel.com>; Maxime Coquelin
> <maxime.coquelin@redhat.com>; Xia, Chenbo <chenbo.xia@intel.com>; David
> Marchand <david.marchand@redhat.com>
> Subject: [PATCH v4] vhost: add new `rte_vhost_vring_call_nonblock` API
> 
> Vhost-user library locks all VQ's access lock when processing
> vring based messages, such as SET_VRING_KICK and SET_VRING_CALL,
> and the data processing thread may already be started, e.g: SPDK
> vhost-blk and vhost-scsi will start the data processing thread
> when one vring is ready, then deadlock may happen when SPDK is
> posting interrupts to VM.  Here, we add a new API which allows
> caller to try again later for this case.
> 
> Bugzilla ID: 1015
> Fixes: c5736998305d ("vhost: fix missing virtqueue lock protection")
> 
> Signed-off-by: Changpeng Liu <changpeng.liu@intel.com>
> ---
>  doc/guides/prog_guide/vhost_lib.rst    |  6 ++++++
>  doc/guides/rel_notes/release_22_11.rst |  6 ++++++
>  lib/vhost/rte_vhost.h                  | 15 +++++++++++++
>  lib/vhost/version.map                  |  3 +++
>  lib/vhost/vhost.c                      | 30 ++++++++++++++++++++++++++
>  5 files changed, 60 insertions(+)
> 
> diff --git a/doc/guides/prog_guide/vhost_lib.rst
> b/doc/guides/prog_guide/vhost_lib.rst
> index bad4d819e1..52f0589f51 100644
> --- a/doc/guides/prog_guide/vhost_lib.rst
> +++ b/doc/guides/prog_guide/vhost_lib.rst
> @@ -297,6 +297,12 @@ The following is an overview of some key Vhost API
> functions:
>    Clear in-flight packets which are submitted to async channel in vhost
> async data
>    path. Completed packets are returned to applications through ``pkts``.
> 
> +* ``rte_vhost_vring_call_nonblock(int vid, uint16_t vring_idx)``
> +
> +  Notify the guest that used descriptors have been added to the vring.
> This function
> +  will return -EAGAIN when vq's access lock is held by other thread, user
> should try
> +  again later.
> +
>  * ``rte_vhost_vring_stats_get_names(int vid, uint16_t queue_id, struct
> rte_vhost_stat_name *names, unsigned int size)``
> 
>    This function returns the names of the queue statistics. It requires
> diff --git a/doc/guides/rel_notes/release_22_11.rst
> b/doc/guides/rel_notes/release_22_11.rst
> index 2da8bc9661..b3d1ba043c 100644
> --- a/doc/guides/rel_notes/release_22_11.rst
> +++ b/doc/guides/rel_notes/release_22_11.rst
> @@ -225,6 +225,12 @@ New Features
>    sysfs entries to adjust the minimum and maximum uncore frequency values,
>    which works on Linux with Intel hardware only.
> 
> +* **Added non-blocking notify API to the vhost library.**
> +
> +  Added ``rte_vhost_vring_call_nonblock`` API to notify the guest that
> +  used descriptors have been added to the vring in non-blocking way. User
> +  should check the return value of this API and try again if needed.
> +
>  * **Rewritten pmdinfo script.**
> 
>    The ``dpdk-pmdinfo.py`` script was rewritten to produce valid JSON only.
> diff --git a/lib/vhost/rte_vhost.h b/lib/vhost/rte_vhost.h
> index bb7d86a432..d22b25cd4e 100644
> --- a/lib/vhost/rte_vhost.h
> +++ b/lib/vhost/rte_vhost.h
> @@ -909,6 +909,21 @@ rte_vhost_clr_inflight_desc_packed(int vid, uint16_t
> vring_idx,
>   */
>  int rte_vhost_vring_call(int vid, uint16_t vring_idx);
> 
> +/**
> + * Notify the guest that used descriptors have been added to the vring.
> This
> + * function acts as a memory barrier.  This function will return -EAGAIN
> when
> + * vq's access lock is held by other thread, user should try again later.
> + *
> + * @param vid
> + *  vhost device ID
> + * @param vring_idx
> + *  vring index
> + * @return
> + *  0 on success, -1 on failure, -EAGAIN for another retry
> + */
> +__rte_experimental
> +int rte_vhost_vring_call_nonblock(int vid, uint16_t vring_idx);
> +
>  /**
>   * Get vhost RX queue avail count.
>   *
> diff --git a/lib/vhost/version.map b/lib/vhost/version.map
> index 7a00b65740..c8c44b8326 100644
> --- a/lib/vhost/version.map
> +++ b/lib/vhost/version.map
> @@ -94,6 +94,9 @@ EXPERIMENTAL {
>  	rte_vhost_async_try_dequeue_burst;
>  	rte_vhost_driver_get_vdpa_dev_type;
>  	rte_vhost_clear_queue;
> +
> +	# added in 22.11
> +	rte_vhost_vring_call_nonblock;
>  };
> 
>  INTERNAL {
> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
> index 8740aa2788..ed6efb003f 100644
> --- a/lib/vhost/vhost.c
> +++ b/lib/vhost/vhost.c
> @@ -1317,6 +1317,36 @@ rte_vhost_vring_call(int vid, uint16_t vring_idx)
>  	return 0;
>  }
> 
> +int
> +rte_vhost_vring_call_nonblock(int vid, uint16_t vring_idx)
> +{
> +	struct virtio_net *dev;
> +	struct vhost_virtqueue *vq;
> +
> +	dev = get_device(vid);
> +	if (!dev)
> +		return -1;
> +
> +	if (vring_idx >= VHOST_MAX_VRING)
> +		return -1;
> +
> +	vq = dev->virtqueue[vring_idx];
> +	if (!vq)
> +		return -1;
> +
> +	if (!rte_spinlock_trylock(&vq->access_lock))
> +		return -EAGAIN;
> +
> +	if (vq_is_packed(dev))
> +		vhost_vring_call_packed(dev, vq);
> +	else
> +		vhost_vring_call_split(dev, vq);
> +
> +	rte_spinlock_unlock(&vq->access_lock);
> +
> +	return 0;
> +}
> +
>  uint16_t
>  rte_vhost_avail_entries(int vid, uint16_t queue_id)
>  {
> --
> 2.21.3

Change title to 'vhost: add non-blocking API for posting interrupt'

Applied to next-virtio/main. thanks