better subject:
vhost: uapi to control task mode (owner vs kthread)
On Sun, Feb 23, 2025 at 11:36:20PM +0800, Cindy Lu wrote:
> Add a new UAPI to enable setting the vhost device to task mode.
better:
Add a new UAPI to configure the vhost device to use the kthread mode
> The userspace application can use VHOST_SET_INHERIT_FROM_OWNER
> to configure the mode
... to either owner or kthread.
> 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 <l...@redhat.com>
> ---
> 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.
> + *
> + * 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
