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

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Message-ID: <CACGkMEsDjFgyFFxz9Gdi2dFbk+JHP6cr7e1xGnLYuPBce-aLHw@mail.gmail.com>
Date: Mon, 13 Jan 2025 11:09:13 +0800
From: Jason Wang <jasowang@...hat.com>
To: Cindy Lu <lulu@...hat.com>
Cc: "Michael S. Tsirkin" <mst@...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 Mon, Jan 13, 2025 at 10:36 AM Cindy Lu <lulu@...hat.com> wrote:
>
> 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.

VHOST_SET_INHERIT_FROM_OWNER is for fork() alike behaviour. Without
this ioctl we will go for kthread.

> A Kconfig option is probably
> > sufficient.  "allow legacy threading mode" and default to yes?

How could we block legacy threading mode in this case?

> >
> 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

Thanks

>
> >
> > > ---
> > >  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
> >
>