Re: [PATCH 2/4] vhost-vdpa: Introduce RESUME backend feature bit

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Oct 14, 2022 at 01:58:38PM +0800, Jason Wang wrote:
> On Thu, Oct 13, 2022 at 11:35 PM <sebastien.boeuf@intel.com> wrote:
> >
> > From: Sebastien Boeuf <sebastien.boeuf@intel.com>
> >
> > Userspace knows if the device can be resumed or not by checking this
> > feature bit.
> >
> > It's only exposed if the vdpa driver backend implements the resume()
> > operation callback. Userspace trying to negotiate this feature when it
> > hasn't been exposed will result in an error.
> >
> > Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
> > ---
> >  drivers/vhost/vdpa.c             | 19 ++++++++++++++++++-
> >  include/uapi/linux/vhost_types.h |  2 ++
> >  2 files changed, 20 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > index 166044642fd5..161727e1a9a5 100644
> > --- a/drivers/vhost/vdpa.c
> > +++ b/drivers/vhost/vdpa.c
> > @@ -355,6 +355,14 @@ static bool vhost_vdpa_can_suspend(const struct vhost_vdpa *v)
> >         return ops->suspend;
> >  }
> >
> > +static bool vhost_vdpa_can_resume(const struct vhost_vdpa *v)
> > +{
> > +       struct vdpa_device *vdpa = v->vdpa;
> > +       const struct vdpa_config_ops *ops = vdpa->config;
> > +
> > +       return ops->resume;
> > +}
> > +
> >  static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
> >  {
> >         struct vdpa_device *vdpa = v->vdpa;
> > @@ -602,11 +610,18 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> >                 if (copy_from_user(&features, featurep, sizeof(features)))
> >                         return -EFAULT;
> >                 if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
> > -                                BIT_ULL(VHOST_BACKEND_F_SUSPEND)))
> > +                                BIT_ULL(VHOST_BACKEND_F_SUSPEND) |
> > +                                BIT_ULL(VHOST_BACKEND_F_RESUME)))
> >                         return -EOPNOTSUPP;
> >                 if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
> >                      !vhost_vdpa_can_suspend(v))
> >                         return -EOPNOTSUPP;
> > +               if ((features & BIT_ULL(VHOST_BACKEND_F_RESUME)) &&
> > +                    !vhost_vdpa_can_resume(v))
> > +                       return -EOPNOTSUPP;
> > +               if (!(features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
> > +                    (features & BIT_ULL(VHOST_BACKEND_F_RESUME)))
> > +                       return -EINVAL;
> 
> Is it better to do the check during the probe? It should be a bug that
> we're having a parent that can only do resume but not suspend.
> 
> Thanks

well we separated them in the spec ...
suspend could have other uses, I won't say it's an invalid
config.

> >                 vhost_set_backend_features(&v->vdev, features);
> >                 return 0;
> >         }
> > @@ -658,6 +673,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
> >                 features = VHOST_VDPA_BACKEND_FEATURES;
> >                 if (vhost_vdpa_can_suspend(v))
> >                         features |= BIT_ULL(VHOST_BACKEND_F_SUSPEND);
> > +               if (vhost_vdpa_can_resume(v))
> > +                       features |= BIT_ULL(VHOST_BACKEND_F_RESUME);
> >                 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 53601ce2c20a..c5690a8992d8 100644
> > --- a/include/uapi/linux/vhost_types.h
> > +++ b/include/uapi/linux/vhost_types.h
> > @@ -163,5 +163,7 @@ struct vhost_vdpa_iova_range {
> >  #define VHOST_BACKEND_F_IOTLB_ASID  0x3
> >  /* Device can be suspended */
> >  #define VHOST_BACKEND_F_SUSPEND  0x4
> > +/* Device can be resumed */
> > +#define VHOST_BACKEND_F_RESUME  0x5
> >
> >  #endif
> > --
> > 2.34.1
> >
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