netdev - Re: [PATCH vhost v4 10/10] virtio_ring: virtqueue_set_dma

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Date: Thu, 21 Mar 2024 14:02:14 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: virtualization@...ts.linux.dev, "Michael S. Tsirkin" <mst@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH vhost v4 10/10] virtio_ring: virtqueue_set_dma_premapped
 support disable

On Tue, Mar 12, 2024 at 11:36 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> Now, the API virtqueue_set_dma_premapped just support to
> enable premapped mode.
>
> If we allow enabling the premapped dynamically, we should
> make this API to support disable the premapped mode.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/virtio/virtio_ring.c | 34 ++++++++++++++++++++++++++--------
>  include/linux/virtio.h       |  2 +-
>  2 files changed, 27 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 34f4b2c0c31e..3bf69cae4965 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -2801,6 +2801,7 @@ EXPORT_SYMBOL_GPL(virtqueue_resize);
>  /**
>   * virtqueue_set_dma_premapped - set the vring premapped mode
>   * @_vq: the struct virtqueue we're talking about.
> + * @premapped: enable/disable the premapped mode.
>   *
>   * Enable the premapped mode of the vq.
>   *
> @@ -2819,9 +2820,10 @@ EXPORT_SYMBOL_GPL(virtqueue_resize);
>   * 0: success.
>   * -EINVAL: vring does not use the dma api, so we can not enable premapped mode.
>   */
> -int virtqueue_set_dma_premapped(struct virtqueue *_vq)
> +int virtqueue_set_dma_premapped(struct virtqueue *_vq, bool premapped)

I think we need to document the requirement for calling this.

Looking at the code, it seems it requires to stop the datapath and
detach all the used buffers?

Thanks