linux-kernel - Re: [PATCH v4 3/4] vhost-vdpa: uAPI to stop the device

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Date:   Wed, 1 Jun 2022 07:03:44 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Eugenio Pérez <eperezma@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
        netdev@...r.kernel.org, martinh@...inx.com,
        Stefano Garzarella <sgarzare@...hat.com>, martinpo@...inx.com,
        lvivier@...hat.com, pabloc@...inx.com,
        Parav Pandit <parav@...dia.com>, Eli Cohen <elic@...dia.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Xie Yongji <xieyongji@...edance.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Zhang Min <zhang.min9@....com.cn>,
        Wu Zongyong <wuzongyong@...ux.alibaba.com>, lulu@...hat.com,
        Zhu Lingshan <lingshan.zhu@...el.com>, Piotr.Uminski@...el.com,
        Si-Wei Liu <si-wei.liu@...cle.com>, ecree.xilinx@...il.com,
        gautam.dawar@....com, habetsm.xilinx@...il.com,
        tanuj.kamde@....com, hanand@...inx.com, dinang@...inx.com,
        Longpeng <longpeng2@...wei.com>
Subject: Re: [PATCH v4 3/4] vhost-vdpa: uAPI to stop the device

On Thu, May 26, 2022 at 02:43:37PM +0200, Eugenio Pérez wrote:
> The ioctl adds support for stop the device from userspace.
> 
> Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> ---
>  drivers/vhost/vdpa.c       | 18 ++++++++++++++++++
>  include/uapi/linux/vhost.h | 14 ++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 32713db5831d..d1d19555c4b7 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -478,6 +478,21 @@ static long vhost_vdpa_get_vqs_count(struct vhost_vdpa *v, u32 __user *argp)
>  	return 0;
>  }
>  
> +static long vhost_vdpa_stop(struct vhost_vdpa *v, u32 __user *argp)
> +{
> +	struct vdpa_device *vdpa = v->vdpa;
> +	const struct vdpa_config_ops *ops = vdpa->config;
> +	int stop;
> +
> +	if (!ops->stop)
> +		return -EOPNOTSUPP;
> +
> +	if (copy_from_user(&stop, argp, sizeof(stop)))
> +		return -EFAULT;
> +
> +	return ops->stop(vdpa, stop);
> +}
> +
>  static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>  				   void __user *argp)
>  {
> @@ -650,6 +665,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>  	case VHOST_VDPA_GET_VQS_COUNT:
>  		r = vhost_vdpa_get_vqs_count(v, argp);
>  		break;
> +	case VHOST_VDPA_STOP:
> +		r = vhost_vdpa_stop(v, argp);
> +		break;
>  	default:
>  		r = vhost_dev_ioctl(&v->vdev, cmd, argp);
>  		if (r == -ENOIOCTLCMD)
> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> index cab645d4a645..c7e47b29bf61 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -171,4 +171,18 @@
>  #define VHOST_VDPA_SET_GROUP_ASID	_IOW(VHOST_VIRTIO, 0x7C, \
>  					     struct vhost_vring_state)
>  
> +/* Stop or resume a device so it does not process virtqueue requests anymore
> + *
> + * After the return of ioctl with stop != 0, the device must finish any
> + * pending operations like in flight requests. It must also preserve all
> + * the necessary state (the virtqueue vring base plus the possible device
> + * specific states) that is required for restoring in the future. The
> + * device must not change its configuration after that point.
> + *
> + * After the return of ioctl with stop == 0, the device can continue
> + * processing buffers as long as typical conditions are met (vq is enabled,
> + * DRIVER_OK status bit is enabled, etc).
> + */
> +#define VHOST_VDPA_STOP			_IOW(VHOST_VIRTIO, 0x7D, int)
> +
>  #endif

I wonder how does this interact with the admin vq idea.
I.e. if we stop all VQs then apparently admin vq can't
work either ...
Thoughts?

> -- 
> 2.31.1