netdev - [PATCH] vhost: add a new ioctl VHOST_GET_VRING_WORKER

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Message-Id: <20251027102644.622305-1-nhudson@akamai.com>
Date: Mon, 27 Oct 2025 10:26:44 +0000
From: Nick Hudson <nhudson@...mai.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
        Eugenio Pérez <eperezma@...hat.com>
Cc: Nick Hudson <nhudson@...mai.com>, Max Tottenham <mtottenh@...mai.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux.dev,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] vhost: add a new ioctl VHOST_GET_VRING_WORKER_INFO and use in net.c

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 <nhudson@...mai.com>
Reviewed-by: Max Tottenham <mtottenh@...mai.com>
---
 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;
+
+	__kernel_pid_t worker_pid;  /* PID/TID of worker thread, -1 if none */
+};
+
 /* no alignment requirement */
 struct vhost_iotlb_msg {
 	__u64 iova;
diff --git a/kernel/vhost_task.c b/kernel/vhost_task.c
index 27107dcc1cbf..aa87a7f0c98a 100644
--- a/kernel/vhost_task.c
+++ b/kernel/vhost_task.c
@@ -67,6 +67,18 @@ static int vhost_task_fn(void *data)
 	do_exit(0);
 }
 
+/**
+ * vhost_get_task - get a pointer to the vhost_task's task_struct
+ * @vtsk: vhost_task to return the task for
+ *
+ * return the vhost_task's task.
+ */
+struct task_struct *vhost_get_task(struct vhost_task *vtsk)
+{
+	return vtsk->task;
+}
+EXPORT_SYMBOL_GPL(vhost_get_task);
+
 /**
  * vhost_task_wake - wakeup the vhost_task
  * @vtsk: vhost_task to wake
-- 
2.34.1