On Wed, Feb 26, 2025 at 5:05 PM Stefano Garzarella [off-list ref] wrote:

On Sun, Feb 23, 2025 at 11:36:20PM +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>
---
drivers/vhost/vhost.c      | 24 ++++++++++++++++++++++--
include/uapi/linux/vhost.h | 18 ++++++++++++++++++
2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index d8c0ea118bb1..45d8f5c5bca9 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -1133,7 +1133,7 @@ void vhost_dev_reset_owner(struct vhost_dev *dev, struct vhost_iotlb *umem)
      int i;

      vhost_dev_cleanup(dev);
-
+      dev->inherit_owner = true;
      dev->umem = umem;
      /* We don't need VQ locks below since vhost_dev_cleanup makes sure
       * VQs aren't running.

@@ -2278,15 +2278,35 @@ 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_FORK_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..8f558b433536 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_FORK_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.

Should we document that this (inherit_owner = 1) is the default, so if
the user doesn't call VHOST_FORK_FROM_OWNER, this mode will be
automatically selected?

Thanks,
Stefano

sure, I will add this
thanks
cindy

quoted

+ *
+ * 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_FORK_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, __u8)
+
#endif
--
2.45.0