linux-kernel - Re: [PATCH V3 3/9] virtio: introduce config op to synchronize vring callbacks

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Date:   Thu, 28 Apr 2022 11:13:22 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Jason Wang <jasowang@...hat.com>, jasowang@...hat.com,
        mst@...hat.com, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Cc:     sgarzare@...hat.com, eperezma@...hat.com, lulu@...hat.com,
        tglx@...utronix.de, peterz@...radead.org, paulmck@...nel.org,
        maz@...nel.org, pasic@...ux.ibm.com
Subject: Re: [PATCH V3 3/9] virtio: introduce config op to synchronize vring
 callbacks

On Mon, Apr 25 2022, Jason Wang <jasowang@...hat.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

Which kind of writes? I.e., what is the scope?

> called after the return of this function. For the transport that
> doesn't provide synchronize_vqs(), use synchornize_rcu() which

Typo: synchronize_rcu()

> synchronize with IRQ implicitly as a fallback.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: "Paul E. McKenney" <paulmck@...nel.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Halil Pasic <pasic@...ux.ibm.com>
> Cc: Cornelia Huck <cohuck@...hat.com>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  include/linux/virtio_config.h | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index b341dd62aa4d..14fe89ff99c7 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -57,6 +57,10 @@ 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)
> + *      Make sure the writes commited before this method is visible to
> + *      vring_interrupt() which is called after this method.

Same here, I think the description needs to be a bit more explicit about
which writes we care about here.

> + *      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 +93,7 @@ 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);