[PATCH v4 7/8] vhost: Add new UAPI to support change to task mode

Cindy Lu
2024-12-10T16:46:06Z

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 <lulu@redhat.com>
---
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