Re: [PATCH v4 3/4] vhost-vdpa: uAPI to stop the device

[Eugenio Perez Martin]

On Wed, Jun 1, 2022 at 1:03 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Thu, May 26, 2022 at 02:43:37PM +0200, Eugenio Pérez wrote:
> > The ioctl adds support for stop the device from userspace.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
> > ---
> >  drivers/vhost/vdpa.c       | 18 ++++++++++++++++++
> >  include/uapi/linux/vhost.h | 14 ++++++++++++++
> >  2 files changed, 32 insertions(+)
> >
> > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > index 32713db5831d..d1d19555c4b7 100644
> > --- a/drivers/vhost/vdpa.c
> > +++ b/drivers/vhost/vdpa.c
> > @@ -478,6 +478,21 @@ static long vhost_vdpa_get_vqs_count(struct vhost_vdpa *v, u32 __user *argp)
> >       return 0;
> >  }
> >
> > +static long vhost_vdpa_stop(struct vhost_vdpa *v, u32 __user *argp)
> > +{
> > +     struct vdpa_device *vdpa = v->vdpa;
> > +     const struct vdpa_config_ops *ops = vdpa->config;
> > +     int stop;
> > +
> > +     if (!ops->stop)
> > +             return -EOPNOTSUPP;
> > +
> > +     if (copy_from_user(&stop, argp, sizeof(stop)))
> > +             return -EFAULT;
> > +
> > +     return ops->stop(vdpa, stop);
> > +}
> > +
> >  static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
> >                                  void __user *argp)
> >  {
> > @@ -650,6 +665,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> >       case VHOST_VDPA_GET_VQS_COUNT:
> >               r = vhost_vdpa_get_vqs_count(v, argp);
> >               break;
> > +     case VHOST_VDPA_STOP:
> > +             r = vhost_vdpa_stop(v, argp);
> > +             break;
> >       default:
> >               r = vhost_dev_ioctl(&v->vdev, cmd, argp);
> >               if (r == -ENOIOCTLCMD)
> > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> > index cab645d4a645..c7e47b29bf61 100644
> > --- a/include/uapi/linux/vhost.h
> > +++ b/include/uapi/linux/vhost.h
> > @@ -171,4 +171,18 @@
> >  #define VHOST_VDPA_SET_GROUP_ASID    _IOW(VHOST_VIRTIO, 0x7C, \
> >                                            struct vhost_vring_state)
> >
> > +/* Stop or resume a device so it does not process virtqueue requests anymore
> > + *
> > + * After the return of ioctl with stop != 0, the device must finish any
> > + * pending operations like in flight requests. It must also preserve all
> > + * the necessary state (the virtqueue vring base plus the possible device
> > + * specific states) that is required for restoring in the future. The
> > + * device must not change its configuration after that point.
> > + *
> > + * After the return of ioctl with stop == 0, the device can continue
> > + * processing buffers as long as typical conditions are met (vq is enabled,
> > + * DRIVER_OK status bit is enabled, etc).
> > + */
> > +#define VHOST_VDPA_STOP                      _IOW(VHOST_VIRTIO, 0x7D, int)
> > +
> >  #endif
>
> I wonder how does this interact with the admin vq idea.
> I.e. if we stop all VQs then apparently admin vq can't
> work either ...
> Thoughts?
>

Copying here the answer to Parav, feel free to answer to any thread or
highlight if I missed something :). Using the admin vq proposal
terminology of "device group".

--
This would stop a device of a device
group, but not the whole virtqueue group. If the admin VQ is offered
by the PF (since it's not exposed to the guest), it will continue
accepting requests as normal. If it's exposed in the VF, I think the
best bet is to shadow it, since guest and host requests could
conflict.

Since this is offered through vdpa, the device backend driver can
route it to whatever method works better for the hardware. For
example, to send an admin vq command to the PF. That's why it's
important to keep the feature as self-contained and orthogonal to
others as possible.
--

> > --
> > 2.31.1
>