Re: [dpdk-dev] [PATCH v5 3/5] vhost: handle memory hotplug for async vhost

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

Hi Cheng & Jiayu,

> -----Original Message-----
> From: Jiang, Cheng1 <cheng1.jiang@intel.com>
> Sent: Friday, July 16, 2021 3:25 PM
> To: maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>
> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Yang, YvonneX
> <yvonnex.yang@intel.com>
> Subject: [PATCH v5 3/5] vhost: handle memory hotplug for async vhost
> 
> From: Jiayu Hu <jiayu.hu@intel.com>
> 
> When the guest memory is hotplugged, the vhost application which
> enables DMA acceleration must stop DMA transfers before the vhost
> re-maps the guest memory.
> 
> This patch is to notify the vhost application of stopping DMA
> transfers.
> 
> Signed-off-by: Jiayu Hu <jiayu.hu@intel.com>
> ---
>  lib/vhost/vhost_user.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> index 031c578e54..39e8432d1c 100644
> --- a/lib/vhost/vhost_user.c
> +++ b/lib/vhost/vhost_user.c
> @@ -1275,6 +1275,15 @@ vhost_user_set_mem_table(struct virtio_net **pdev,
> struct VhostUserMsg *msg,
>  				vdpa_dev->ops->dev_close(dev->vid);
>  			dev->flags &= ~VIRTIO_DEV_VDPA_CONFIGURED;
>  		}
> +
> +		/* notify the backend application to stop DMA transfers */

Backend application -> vhost application

> +		if (dev->async_copy && dev->notify_ops->vring_state_changed) {
> +			for (i = 0; i < dev->nr_vring; i++) {
> +				dev->notify_ops->vring_state_changed(dev->vid,
> +						i, 0);
> +			}
> +		}
> +

In this case, I think app will never know the vring is enabled again with memory
table updated.

Thanks,
Chenbo  

>  		free_mem_region(dev);
>  		rte_free(dev->mem);
>  		dev->mem = NULL;
> --
> 2.29.2