linux-kernel - Re: [RFC 7/7] vhost: Add new UAPI to support changing Kthread mode

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Message-ID: <CACGkMEt2O2r7BDLYq0Yus7KP17N_DMUP9OoRMbvqC5V0N6rs7w@mail.gmail.com>
Date: Tue, 27 Aug 2024 10:36:43 +0800
From: Jason Wang <jasowang@...hat.com>
To: Cindy Lu <lulu@...hat.com>
Cc: mst@...hat.com, linux-kernel@...r.kernel.org, 
	virtualization@...ts.linux-foundation.org
Subject: Re: [RFC 7/7] vhost: Add new UAPI to support changing Kthread mode

On Mon, Aug 19, 2024 at 5:29 PM Cindy Lu <lulu@...hat.com> wrote:
>
> Add a new UAPI to support setting the vhost device to
> use kthread mode. The user space application needs to use
> VHOST_SET_USE_KTHREAD to set the mode. This setting must
> be set before VHOST_SET_OWNER is set.
>
> Signed-off-by: Cindy Lu <lulu@...hat.com>
> ---
>  drivers/vhost/vhost.c      | 11 ++++++++++-
>  include/uapi/linux/vhost.h |  2 ++
>  2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 0a7b2999100f..d6b71bddc272 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2340,14 +2340,23 @@ 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;
> +       bool kthread;
>
>         /* 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_USE_KTHREAD) {

Btw, should we enforce this to be called when there's no owner?

> +               if (copy_from_user(&kthread, argp, sizeof(kthread))) {
> +                       r = -EFAULT;
> +                       goto done;
> +               }
> +               use_kthread = kthread;
> +               goto done;
> +       }
>
>         /* You must be the owner to do anything else */
>         r = vhost_dev_check_owner(d);
> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> index b95dd84eef2d..386fe735da63 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -235,4 +235,6 @@
>   */
>  #define VHOST_VDPA_GET_VRING_SIZE      _IOWR(VHOST_VIRTIO, 0x82,       \
>                                               struct vhost_vring_state)
> +
> +#define VHOST_SET_USE_KTHREAD _IOW(VHOST_VIRTIO, 0x83, bool)
>  #endif
> --
> 2.45.0
>

Thanks