[PATCH v8 6/8] vhost: uapi to control task mode (owner vs kthread)

Cindy Lu
2025-03-28T10:05:07Z

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

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
drivers/vhost/vhost.c | 22 ++++++++++++++++++++--
include/uapi/linux/vhost.h | 16 ++++++++++++++++
2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index be97028a8baf..ff930c2e5b78 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1134,7 +1134,7 @@ 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.
@@ -2287,7 +2287,25 @@ 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;
+ }
/* 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.
+ *
+ * @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