Re: [PATCH V6 3/9] virtio: introduce config op to synchronize vring callbacks

Xuan Zhuo
2022-05-27T07:31:00Z

On Fri, 27 May 2022 14:01:14 +0800, Jason Wang <jasowang@redhat.com> wrote:
> This patch introduces new virtio config op to vring
> callbacks. Transport specific method is required to make sure the
> write before this function is visible to the vring_interrupt() that is
> called after the return of this function. For the transport that
> doesn't provide synchronize_vqs(), use synchornize_rcu() which
> synchronize with IRQ implicitly as a fallback.
>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Halil Pasic <pasic@linux.ibm.com>
> Cc: Cornelia Huck <cohuck@redhat.com>
> Cc: Vineeth Vijayan <vneethv@linux.ibm.com>
> Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
> Cc: linux-s390@vger.kernel.org
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

> ---
> include/linux/virtio_config.h | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index b341dd62aa4d..25be018810a7 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -57,6 +57,11 @@ struct virtio_shm_region {
> * include a NULL entry for vqs unused by driver
> * Returns 0 on success or error status
> * @del_vqs: free virtqueues found by find_vqs().
> + * @synchronize_cbs: synchronize with the virtqueue callbacks (optional)
> + * The function guarantees that all memory operations on the
> + * queue before it are visible to the vring_interrupt() that is
> + * called after it.
> + * vdev: the virtio_device
> * @get_features: get the array of feature bits for this device.
> * vdev: the virtio_device
> * Returns the first 64 feature bits (all we currently need).
> @@ -89,6 +94,7 @@ struct virtio_config_ops {
> const char * const names[], const bool *ctx,
> struct irq_affinity *desc);
> void (*del_vqs)(struct virtio_device *);
> + void (*synchronize_cbs)(struct virtio_device *);
> u64 (*get_features)(struct virtio_device *vdev);
> int (*finalize_features)(struct virtio_device *vdev);
> const char *(*bus_name)(struct virtio_device *vdev);
> @@ -217,6 +223,25 @@ int virtio_find_vqs_ctx(struct virtio_device *vdev, unsigned nvqs,
> desc);
> }
>
> +/**
> + * virtio_synchronize_cbs - synchronize with virtqueue callbacks
> + * @vdev: the device
> + */
> +static inline
> +void virtio_synchronize_cbs(struct virtio_device *dev)
> +{
> + if (dev->config->synchronize_cbs) {
> + dev->config->synchronize_cbs(dev);
> + } else {
> + /*
> + * A best effort fallback to synchronize with
> + * interrupts, preemption and softirq disabled
> + * regions. See comment above synchronize_rcu().
> + */
> + synchronize_rcu();
> + }
> +}
> +
> /**
> * virtio_device_ready - enable vq use in probe function
> * @vdev: the device
> --
> 2.25.1
>