Re: [PATCH 2/4] vhost-vdpa: introduce STOP backend feature bit

[Eugenio Perez Martin]

On Sat, May 21, 2022 at 12:25 PM Si-Wei Liu <si-wei.liu@xxxxxxxxxx> wrote:
>
>
>
> On 5/20/2022 10:23 AM, Eugenio Pérez wrote:
> > Userland knows if it can stop the device or not by checking this feature
> > bit.
> >
> > It's only offered if the vdpa driver backend implements the stop()
> > operation callback, and try to set it if the backend does not offer that
> > callback is an error.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
> > ---
> >   drivers/vhost/vdpa.c             | 13 +++++++++++++
> >   include/uapi/linux/vhost_types.h |  2 ++
> >   2 files changed, 15 insertions(+)
> >
> > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > index 1f1d1c425573..a325bc259afb 100644
> > --- a/drivers/vhost/vdpa.c
> > +++ b/drivers/vhost/vdpa.c
> > @@ -347,6 +347,14 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
> >       return 0;
> >   }
> >
> > +static bool vhost_vdpa_can_stop(const struct vhost_vdpa *v)
> > +{
> > +     struct vdpa_device *vdpa = v->vdpa;
> > +     const struct vdpa_config_ops *ops = vdpa->config;
> > +
> > +     return ops->stop;
> > +}
> > +
> >   static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
> >   {
> >       struct vdpa_device *vdpa = v->vdpa;
> > @@ -577,6 +585,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> >                       return -EFAULT;
> >               if (features & ~VHOST_VDPA_BACKEND_FEATURES)
> >                       return -EOPNOTSUPP;
> > +             if ((features & VHOST_BACKEND_F_STOP) &&
> VHOST_BACKEND_F_STOP is not part of VHOST_VDPA_BACKEND_FEATURES. There's
> no chance for VHOST_BACKEND_F_STOP to get here.
>

That's right. I think I missed to backport your patches about set
backend_features only once in my testing.

I will re-test with the latest qemu master, thanks!

> -Siwei
> > +                  !vhost_vdpa_can_stop(v))
> > +                     return -EOPNOTSUPP;
> >               vhost_set_backend_features(&v->vdev, features);
> >               return 0;
> >       }
> > @@ -624,6 +635,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> >               break;
> >       case VHOST_GET_BACKEND_FEATURES:
> >               features = VHOST_VDPA_BACKEND_FEATURES;
> > +             if (vhost_vdpa_can_stop(v))
> > +                     features |= VHOST_BACKEND_F_STOP;
> >               if (copy_to_user(featurep, &features, sizeof(features)))
> >                       r = -EFAULT;
> >               break;
> > diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> > index 634cee485abb..2758e665791b 100644
> > --- a/include/uapi/linux/vhost_types.h
> > +++ b/include/uapi/linux/vhost_types.h
> > @@ -161,5 +161,7 @@ struct vhost_vdpa_iova_range {
> >    * message
> >    */
> >   #define VHOST_BACKEND_F_IOTLB_ASID  0x3
> > +/* Stop device from processing virtqueue buffers */
> > +#define VHOST_BACKEND_F_STOP  0x4
> >
> >   #endif
>