linux-kernel - Re: [PATCH v7 3/4] vhost-vdpa: uAPI to suspend the device

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Date:   Thu, 11 Aug 2022 04:29:06 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Eugenio Pérez <eperezma@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        dinang@...inx.com, martinpo@...inx.com,
        Wu Zongyong <wuzongyong@...ux.alibaba.com>,
        Piotr.Uminski@...el.com, gautam.dawar@....com,
        ecree.xilinx@...il.com, martinh@...inx.com,
        Stefano Garzarella <sgarzare@...hat.com>, pabloc@...inx.com,
        habetsm.xilinx@...il.com, lvivier@...hat.com,
        Zhu Lingshan <lingshan.zhu@...el.com>, tanuj.kamde@....com,
        Longpeng <longpeng2@...wei.com>, lulu@...hat.com,
        hanand@...inx.com, Parav Pandit <parav@...dia.com>,
        Si-Wei Liu <si-wei.liu@...cle.com>,
        Eli Cohen <elic@...dia.com>,
        Xie Yongji <xieyongji@...edance.com>,
        Zhang Min <zhang.min9@....com.cn>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: Re: [PATCH v7 3/4] vhost-vdpa: uAPI to suspend the device

On Wed, Aug 10, 2022 at 07:15:11PM +0200, Eugenio Pérez wrote:
> The ioctl adds support for suspending the device from userspace.
> 
> This is a must before getting virtqueue indexes (base) for live migration,
> since the device could modify them after userland gets them. There are
> individual ways to perform that action for some devices
> (VHOST_NET_SET_BACKEND, VHOST_VSOCK_SET_RUNNING, ...) but there was no
> way to perform it for any vhost device (and, in particular, vhost-vdpa).
> 
> After a successful return of the ioctl call the device must not process
> more virtqueue descriptors. The device can answer to read or writes of
> config fields as if it were not suspended. In particular, writing to
> "queue_enable" with a value of 1 will not make the device start
> processing buffers of the virtqueue.
> 
> Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> Message-Id: <20220623160738.632852-4-eperezma@...hat.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

You are not supposed to include upstream maintainer's signoff
like this.

> ---
> v7: Delete argument to ioctl, unused
> ---
>  drivers/vhost/vdpa.c       | 19 +++++++++++++++++++
>  include/uapi/linux/vhost.h |  9 +++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 3d636e192061..7fa671ac4bdf 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -478,6 +478,22 @@ static long vhost_vdpa_get_vqs_count(struct vhost_vdpa *v, u32 __user *argp)
>  	return 0;
>  }
>  
> +/* After a successful return of ioctl the device must not process more
> + * virtqueue descriptors. The device can answer to read or writes of config
> + * fields as if it were not suspended. In particular, writing to "queue_enable"
> + * with a value of 1 will not make the device start processing buffers.
> + */
> +static long vhost_vdpa_suspend(struct vhost_vdpa *v)
> +{
> +	struct vdpa_device *vdpa = v->vdpa;
> +	const struct vdpa_config_ops *ops = vdpa->config;
> +
> +	if (!ops->suspend)
> +		return -EOPNOTSUPP;
> +
> +	return ops->suspend(vdpa);
> +}
> +
>  static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>  				   void __user *argp)
>  {
> @@ -654,6 +670,9 @@ 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_SUSPEND:
> +		r = vhost_vdpa_suspend(v);
> +		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..f9f115a7c75b 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -171,4 +171,13 @@
>  #define VHOST_VDPA_SET_GROUP_ASID	_IOW(VHOST_VIRTIO, 0x7C, \
>  					     struct vhost_vring_state)
>  
> +/* Suspend a device so it does not process virtqueue requests anymore
> + *
> + * After the return of ioctl the device must 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.
> + */
> +#define VHOST_VDPA_SUSPEND		_IO(VHOST_VIRTIO, 0x7D)
> +
>  #endif
> -- 
> 2.31.1