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

Michael S. Tsirkin
2025-01-08T12:13:35Z

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

Good. I would like to see an option to allow/block this ioctl,
to prevent exceeding nproc limits. A Kconfig option is probably
sufficient. "allow legacy threading mode" and default to yes?

> ---
> 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