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Date:   Sat, 21 May 2022 03:24:50 -0700
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Subject: Re: [PATCH 2/4] vhost-vdpa: introduce STOP backend feature bit
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To:     =?UTF-8?Q?Eugenio_P=c3=a9rez?= <eperezma@redhat.com>,
        virtualization@lists.linux-foundation.org,
        Jason Wang <jasowang@redhat.com>, kvm@vger.kernel.org,
        "Michael S. Tsirkin" <mst@redhat.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Stefano Garzarella <sgarzare@redhat.com>,
        Longpeng <longpeng2@huawei.com>,
        Zhu Lingshan <lingshan.zhu@intel.com>, martinh@xilinx.com,
        hanand@xilinx.com, dinang@xilinx.com, Eli Cohen <elic@nvidia.com>,
        lvivier@redhat.com, pabloc@xilinx.com, gautam.dawar@amd.com,
        Xie Yongji <xieyongji@bytedance.com>, habetsm.xilinx@gmail.com,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        tanuj.kamde@amd.com, Wu Zongyong <wuzongyong@linux.alibaba.com>,
        martinpo@xilinx.com, lulu@redhat.com, ecree.xilinx@gmail.com,
        Parav Pandit <parav@nvidia.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Zhang Min <zhang.min9@zte.com.cn>
References: <20220520172325.980884-1-eperezma@redhat.com>
 <20220520172325.980884-3-eperezma@redhat.com>
From:   Si-Wei Liu <si-wei.liu@oracle.com>
Organization: Oracle Corporation
In-Reply-To: <20220520172325.980884-3-eperezma@redhat.com>
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On 5/20/2022 10:23 AM, Eugenio Pérez wrote:
> Userland knows if it can stop the device or not by checking this feature
> bit.
>
> It's only offered if the vdpa driver backend implements the stop()
> operation callback, and try to set it if the backend does not offer that
> callback is an error.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   drivers/vhost/vdpa.c             | 13 +++++++++++++
>   include/uapi/linux/vhost_types.h |  2 ++
>   2 files changed, 15 insertions(+)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 1f1d1c425573..a325bc259afb 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -347,6 +347,14 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
>   	return 0;
>   }
>   
> +static bool vhost_vdpa_can_stop(const struct vhost_vdpa *v)
> +{
> +	struct vdpa_device *vdpa = v->vdpa;
> +	const struct vdpa_config_ops *ops = vdpa->config;
> +
> +	return ops->stop;
> +}
> +
>   static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
>   {
>   	struct vdpa_device *vdpa = v->vdpa;
> @@ -577,6 +585,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>   			return -EFAULT;
>   		if (features & ~VHOST_VDPA_BACKEND_FEATURES)
>   			return -EOPNOTSUPP;
> +		if ((features & VHOST_BACKEND_F_STOP) &&
VHOST_BACKEND_F_STOP is not part of VHOST_VDPA_BACKEND_FEATURES. There's 
no chance for VHOST_BACKEND_F_STOP to get here.

-Siwei
> +		     !vhost_vdpa_can_stop(v))
> +			return -EOPNOTSUPP;
>   		vhost_set_backend_features(&v->vdev, features);
>   		return 0;
>   	}
> @@ -624,6 +635,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>   		break;
>   	case VHOST_GET_BACKEND_FEATURES:
>   		features = VHOST_VDPA_BACKEND_FEATURES;
> +		if (vhost_vdpa_can_stop(v))
> +			features |= VHOST_BACKEND_F_STOP;
>   		if (copy_to_user(featurep, &features, sizeof(features)))
>   			r = -EFAULT;
>   		break;
> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> index 634cee485abb..2758e665791b 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -161,5 +161,7 @@ struct vhost_vdpa_iova_range {
>    * message
>    */
>   #define VHOST_BACKEND_F_IOTLB_ASID  0x3
> +/* Stop device from processing virtqueue buffers */
> +#define VHOST_BACKEND_F_STOP  0x4
>   
>   #endif