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

Cindy Lu
2025-01-22T02:08:02Z

Ping for review, Hi MST and Jason, do you have any comments on this?
Thanks
Cindy
On Mon, Jan 13, 2025 at 11:09 AM Jason Wang <jasowang@redhat.com> wrote:
>
> On Mon, Jan 13, 2025 at 10:36 AM Cindy Lu <lulu@redhat.com> wrote:
> >
> > On Wed, Jan 8, 2025 at 8:13 PM Michael S. Tsirkin <mst@redhat.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@redhat.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
> > >
> >
>