linux-kernel - Re: [PATCH v6 5/6] vhost: Add new UAPI to support change to task mode

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Message-ID: <CACLfguWpj=-Ad3o731xbRdGRr3NT6oEQ67Z-FPBmd93gYEhAXw@mail.gmail.com>
Date: Wed, 26 Feb 2025 14:16:09 +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 v6 5/6] vhost: Add new UAPI to support change to task mode

On Tue, Feb 25, 2025 at 5:46 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> 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
>
Thanks MST, will change this
>
> > The userspace application can use VHOST_SET_INHERIT_FROM_OWNER
> > to configure the mode
>
> ... to either owner or kthread.
>
sure, will change this
thanks
cindy
>
> > 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>
> > ---
> >  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
>