On Mon, Apr 21, 2025 at 10:44:09AM +0800, Cindy Lu wrote:
Add a new UAPI to configure the vhost device to use the kthread mode.
The userspace application can use IOCTL VHOST_FORK_FROM_OWNER
to choose between owner and kthread mode if necessary.
This setting must be applied before VHOST_SET_OWNER, as the worker
will be created in the VHOST_SET_OWNER function.
In addition, the VHOST_NEW_WORKER requires the inherit_owner
setting to be true. So we need to add a check for this.
Signed-off-by: Cindy Lu <l...@redhat.com>
---
drivers/vhost/vhost.c | 29 +++++++++++++++++++++++++++--
include/uapi/linux/vhost.h | 16 ++++++++++++++++
2 files changed, 43 insertions(+), 2 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index be97028a8baf..fb0c7fb43f78 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1018,6 +1018,13 @@ long vhost_worker_ioctl(struct vhost_dev *dev, unsigned
int ioctl,
switch (ioctl) {
/* dev worker ioctls */
case VHOST_NEW_WORKER:
+ /*
+ * vhost_tasks will account for worker threads under the
parent's
+ * NPROC value but kthreads do not. To avoid userspace
overflowing
+ * the system with worker threads inherit_owner must be true.
+ */
+ if (!dev->inherit_owner)
+ return -EFAULT;
ret = vhost_new_worker(dev, &state);
if (!ret && copy_to_user(argp, &state, sizeof(state)))
ret = -EFAULT;
@@ -1134,7 +1141,7 @@ void vhost_dev_reset_owner(struct vhost_dev *dev, struct
vhost_iotlb *umem)
int i;
vhost_dev_cleanup(dev);
-
nit: I'd avoid removing this empty line, it helps while reading code.
+ dev->inherit_owner = true;
dev->umem = umem;
/* We don't need VQ locks below since vhost_dev_cleanup makes sure
* VQs aren't running.
@@ -2287,7 +2294,25 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int
ioctl, void __user *argp)
r = vhost_dev_set_owner(d);
goto done;
}
-
+ if (ioctl == VHOST_FORK_FROM_OWNER) {
+ u8 inherit_owner;
+ /*inherit_owner can only be modified before owner is set*/
+ if (vhost_dev_has_owner(d)) {
+ r = -EBUSY;
+ goto done;
+ }
+ if (copy_from_user(&inherit_owner, argp, sizeof(u8))) {
+ r = -EFAULT;
+ goto done;
+ }
+ if (inherit_owner > 1) {
+ r = -EINVAL;
+ goto done;
+ }
+ d->inherit_owner = (bool)inherit_owner;
+ r = 0;
+ goto done;
+ }
Ditto, an empty like should help to separate to the next step.
/* You must be the owner to do anything else */
r = vhost_dev_check_owner(d);
if (r)
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index b95dd84eef2d..1ae0917bfeca 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -235,4 +235,20 @@
*/
#define VHOST_VDPA_GET_VRING_SIZE _IOWR(VHOST_VIRTIO, 0x82, \
struct vhost_vring_state)
+
+/**
+ * VHOST_FORK_FROM_OWNER - Set the inherit_owner flag for the vhost device,
+ * This ioctl must called before VHOST_SET_OWNER.
Shoud we mention that this IOCTL is only supported if
CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is y?
+ *
+ * @param inherit_owner: An 8-bit value that determines the vhost thread mode
+ *
+ * When inherit_owner is set to 1(default value):
+ * - Vhost will create tasks similar to processes forked from the owner,
+ * inheriting all of the owner's attributes.
+ *
+ * When inherit_owner is set to 0:
+ * - Vhost will create tasks as kernel thread.
+ */
+#define VHOST_FORK_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, __u8)
+
#endif
--
2.45.0
