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

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Message-ID: <CACLfguUffb-kTZgUoBnJAJxhpxh-xq8xBM-Hv5CZeWzDoha6tA@mail.gmail.com>
Date: Mon, 13 Jan 2025 10:36:12 +0800
From: Cindy Lu <lulu@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: jasowang@...hat.com, michael.christie@...cle.com, sgarzare@...hat.com, 
	linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH v4 7/8] vhost: Add new UAPI to support change to task mode

On Wed, Jan 8, 2025 at 8:13 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> 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@...hat.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?
>
sure I will add this in the new version, the legacy thread mode here
is  kthread mode
I will change these commit comments and make it more clear
Thanks
Cindy

>
> > ---
> >  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
>