On 28 Oct 2025, at 00:42, Jason Wang [off-list ref] wrote:

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On Mon, Oct 27, 2025 at 6:27 PM Nick Hudson [off-list ref] wrote:

quoted

The vhost_net (and vhost_sock) drivers create worker tasks to handle
the virtual queues. Provide a new ioctl VHOST_GET_VRING_WORKER_INFO that
can be used to determine the PID of these tasks so that, for example,
they can be pinned to specific CPU(s).

Signed-off-by: Nick Hudson <redacted>
Reviewed-by: Max Tottenham <redacted>
---
drivers/vhost/net.c              |  5 +++++
drivers/vhost/vhost.c            | 16 ++++++++++++++++
include/uapi/linux/vhost.h       |  3 +++
include/uapi/linux/vhost_types.h | 13 +++++++++++++
kernel/vhost_task.c              | 12 ++++++++++++
5 files changed, 49 insertions(+)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 35ded4330431..e86bd5d7d202 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c

@@ -1804,6 +1804,11 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
               return vhost_net_reset_owner(n);
       case VHOST_SET_OWNER:
               return vhost_net_set_owner(n);
+       case VHOST_GET_VRING_WORKER_INFO:
+               mutex_lock(&n->dev.mutex);
+               r = vhost_worker_ioctl(&n->dev, ioctl, argp);
+               mutex_unlock(&n->dev.mutex);
+               return r;
       default:
               mutex_lock(&n->dev.mutex);
               r = vhost_dev_ioctl(&n->dev, ioctl, argp);

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 8570fdf2e14a..8b52fd5723c3 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -2399,6 +2399,22 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
               if (ctx)
                       eventfd_ctx_put(ctx);
               break;
+       case VHOST_GET_VRING_WORKER_INFO:
+               worker = rcu_dereference_check(vq->worker,
+                                              lockdep_is_held(&dev->mutex));
+               if (!worker) {
+                       ret = -EINVAL;
+                       break;
+               }
+
+               memset(&ring_worker_info, 0, sizeof(ring_worker_info));
+               ring_worker_info.index = idx;
+               ring_worker_info.worker_id = worker->id;
+               ring_worker_info.worker_pid = task_pid_vnr(vhost_get_task(worker->vtsk));
+
+               if (copy_to_user(argp, &ring_worker_info, sizeof(ring_worker_info)))
+                       ret = -EFAULT;
+               break;
       default:
               r = -ENOIOCTLCMD;
               break;

diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index c57674a6aa0d..c32aa8c71952 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h

@@ -101,6 +101,9 @@

/* Return the vring worker's ID */
#define VHOST_GET_VRING_WORKER _IOWR(VHOST_VIRTIO, 0x16,               \
                                    struct vhost_vring_worker)
+/* Return the vring worker's ID and PID */
+#define VHOST_GET_VRING_WORKER_INFO _IOWR(VHOST_VIRTIO, 0x17,  \
+                                    struct vhost_vring_worker_info)

/* The following ioctls use eventfd file descriptors to signal and poll
 * for events. */

diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
index 1c39cc5f5a31..28e00f8ade85 100644
--- a/include/uapi/linux/vhost_types.h
+++ b/include/uapi/linux/vhost_types.h

@@ -63,6 +63,19 @@ struct vhost_vring_worker {
       unsigned int worker_id;

};

+/* Per-virtqueue worker mapping entry */
+struct vhost_vring_worker_info {
+       /* vring index */
+       unsigned int index;
+       /*
+        * The id of the vhost_worker returned from VHOST_NEW_WORKER or
+        * allocated as part of vhost_dev_set_owner.
+        */
+       unsigned int worker_id;

I'm not sure the above two are a must and exposing internal workd_id
seems not like a good idea.

It’s already exposed by VHOST_NEW_WORKER, but happy to drop it if you prefer.

quoted

+
+       __kernel_pid_t worker_pid;  /* PID/TID of worker thread, -1 if none */

Instead of exposing the worker PID, I wonder if it's simple to just
having a better naming of the worker instead of a simple:

       snprintf(name, sizeof(name), "vhost-%d", current->pid);

This is currently the case

drivers/vhost/vhost.c:  snprintf(name, sizeof(name), "vhost-%d", current->pid);

I was hoping to add the IOCTL, use in qemu, and expose it via QMP/HMP. I have changes to qemu that do this.

Thanks,
Nick