On 2020/12/5 上午12:32, Mike Christie wrote:
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?
My understanding is that it only matter scheduling. And this patch wants
to change the affinity which should check that capability.
If so, then I see the interface needs to be changed.
Actually, if I read this patch correctly it requires e.g qemu to make
the decision instead of the management layer. This may bring some
troubles to for e.g the libvirt emulatorpin[1] implementation.
Thanks
[1]
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/virtualization_tuning_and_optimization_guide/sect-virtualization_tuning_optimization_guide-numa-numa_and_libvirt
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