Re: [RFC PATCH 5/8] vhost: allow userspace to bind vqs to CPUs

[Jason Wang <jasowang@redhat.com>]

On 2020/12/4 下午3:56, Mike Christie wrote:
> +static long vhost_vring_set_cpu(struct vhost_dev *d, struct vhost_virtqueue *vq,
> +				void __user *argp)
> +{
> +	struct vhost_vring_state s;
> +	int ret = 0;
> +
> +	if (vq->private_data)
> +		return -EBUSY;
> +
> +	if (copy_from_user(&s, argp, sizeof s))
> +		return -EFAULT;
> +
> +	if (s.num == -1) {
> +		vq->cpu = s.num;
> +		return 0;
> +	}
> +
> +	if (s.num >= nr_cpu_ids)
> +		return -EINVAL;
> +
> +	if (!d->ops || !d->ops->get_workqueue)
> +		return -EINVAL;
> +
> +	if (!d->wq)
> +		d->wq = d->ops->get_workqueue();
> +	if (!d->wq)
> +		return -EINVAL;
> +
> +	vq->cpu = s.num;
> +	return ret;
> +}


So one question here. Who is in charge of doing this set_cpu? Note 
that sched_setaffinity(2) requires CAP_SYS_NICE to work, so I wonder 
whether or not it's legal for unprivileged Qemu to do this.

Thanks