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

[Mike Christie <michael.christie@oracle.com>]

On 12/4/20 2:09 AM, Jason Wang wrote:
> 
> 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.


I was having qemu do it when it's setting up the vqs since it had the 
info there already.

Is it normally the tool that makes calls into qemu that does the 
operations that require CAP_SYS_NICE? If so, then I see the interface 
needs to be changed.