linux-kernel - Re: [PATCH V5 7/9] virtio: allow to unbreak virtqueue

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Message-ID: <87r14rf983.fsf@redhat.com>
Date:   Wed, 18 May 2022 12:03:56 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Jason Wang <jasowang@...hat.com>, mst@...hat.com,
        jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, peterz@...radead.org, paulmck@...nel.org,
        maz@...nel.org, pasic@...ux.ibm.com, eperezma@...hat.com,
        lulu@...hat.com, sgarzare@...hat.com, xuanzhuo@...ux.alibaba.com,
        Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH V5 7/9] virtio: allow to unbreak virtqueue

On Wed, May 18 2022, Jason Wang <jasowang@...hat.com> wrote:

> This patch allows the new introduced __virtio_break_device() to
> unbreak the virtqueue.
>
> 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>
> Cc: Vineeth Vijayan <vneethv@...ux.ibm.com>
> Cc: Peter Oberparleiter <oberpar@...ux.ibm.com>
> Cc: linux-s390@...r.kernel.org
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/virtio/virtio_ring.c | 21 +++++++++++++++++++++
>  include/linux/virtio.h       |  1 +
>  2 files changed, 22 insertions(+)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index cfb028ca238e..5b7df7c455f0 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2397,6 +2397,27 @@ void virtio_break_device(struct virtio_device *dev)
>  }
>  EXPORT_SYMBOL_GPL(virtio_break_device);
>  
> +/*
> + * This should allow the device to be used by the driver. You may
> + * need to grab appropriate locks to flush. This should only be used

Hm, to flush what?

> + * in some specific case e.g (probing and restoring). Driver should
> + * not call this directly.

Maybe "This function should only be called by the core, not directly by
the driver."?

> + */
> +void __virtio_unbreak_device(struct virtio_device *dev)
> +{
> +	struct virtqueue *_vq;
> +
> +	spin_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(). */
> +		WRITE_ONCE(vq->broken, false);
> +	}
> +	spin_unlock(&dev->vqs_list_lock);
> +}
> +EXPORT_SYMBOL_GPL(__virtio_unbreak_device);
> +
>  dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);