Ping for review, Hi MST and Jason, do you have any comments on this?
Thanks
Cindy
On Mon, Jan 13, 2025 at 11:09 AM Jason Wang [off-list ref] wrote:

On Mon, Jan 13, 2025 at 10:36 AM Cindy Lu [off-list ref] wrote:

quoted

On Wed, Jan 8, 2025 at 8:13 PM Michael S. Tsirkin [off-list ref] wrote:

quoted

On Wed, Dec 11, 2024 at 12:41:46AM +0800, Cindy Lu wrote:

quoted

Add a new UAPI to enable setting the vhost device to task mode.
The userspace application can use VHOST_SET_INHERIT_FROM_OWNER
to configure the mode if necessary.
This setting must be applied before VHOST_SET_OWNER, as the worker
will be created in the VHOST_SET_OWNER function

Signed-off-by: Cindy Lu <redacted>

Good.  I would like to see an option to allow/block this ioctl,
to prevent exceeding nproc limits.

VHOST_SET_INHERIT_FROM_OWNER is for fork() alike behaviour. Without
this ioctl we will go for kthread.

quoted

A Kconfig option is probably

quoted

sufficient.  "allow legacy threading mode" and default to yes?

How could we block legacy threading mode in this case?

quoted

quoted

sure I will add this in the new version, the legacy thread mode here
is  kthread mode
I will change these commit comments and make it more clear
Thanks
Cindy

Thanks

quoted

quoted

quoted

---
 drivers/vhost/vhost.c      | 22 +++++++++++++++++++++-
 include/uapi/linux/vhost.h | 18 ++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3e9cb99da1b5..12c3bf3d1ed4 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -2257,15 +2257,35 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 {
      struct eventfd_ctx *ctx;
      u64 p;
-     long r;
+     long r = 0;
      int i, fd;
+     u8 inherit_owner;

      /* If you are not the owner, you can become one */
      if (ioctl == VHOST_SET_OWNER) {
              r = vhost_dev_set_owner(d);
              goto done;
      }
+     if (ioctl == VHOST_SET_INHERIT_FROM_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;
+             }
+             /* Validate the inherit_owner value, ensuring it is either 0 or 1 */
+             if (inherit_owner > 1) {
+                     r = -EINVAL;
+                     goto done;
+             }
+
+             d->inherit_owner = (bool)inherit_owner;

+             goto done;
+     }
      /* 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..d7564d62b76d 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h

@@ -235,4 +235,22 @@
  */
 #define VHOST_VDPA_GET_VRING_SIZE    _IOWR(VHOST_VIRTIO, 0x82,       \
                                            struct vhost_vring_state)
+
+/**
+ * VHOST_SET_INHERIT_FROM_OWNER - Set the inherit_owner flag for the vhost device
+ *
+ * @param inherit_owner: An 8-bit value that determines the vhost thread mode
+ *
+ * When inherit_owner is set to 1:
+ *   - The VHOST worker threads inherit its values/checks from
+ *     the thread that owns the VHOST device, The vhost threads will
+ *     be counted in the nproc rlimits.
+ *
+ * When inherit_owner is set to 0:
+ *   - The VHOST worker threads will use the traditional kernel thread (kthread)
+ *     implementation, which may be preferred by older userspace applications that
+ *     do not utilize the newer vhost_task concept.
+ */
+#define VHOST_SET_INHERIT_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, __u8)
+
 #endif
--

2.45.0