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From:   Eugenio Perez Martin <eperezma@redhat.com>
Date:   Fri, 8 Jul 2022 13:44:57 +0200
Message-ID: <CAJaqyWdciXkbtpBmGugDsr+0Nh3X50r2Fa5i9Yk2NyQaXBLKtg@mail.gmail.com>
Subject: Re: [PATCH v6 2/4] vhost-vdpa: introduce SUSPEND backend feature bit
To:     Jason Wang <jasowang@redhat.com>
Cc:     netdev <netdev@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        virtualization <virtualization@lists.linux-foundation.org>,
        kvm <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>,
        Parav Pandit <parav@nvidia.com>,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Cindy Lu <lulu@redhat.com>,
        "Kamde, Tanuj" <tanuj.kamde@amd.com>,
        Si-Wei Liu <si-wei.liu@oracle.com>,
        "Uminski, Piotr" <Piotr.Uminski@intel.com>,
        habetsm.xilinx@gmail.com, "Dawar, Gautam" <gautam.dawar@amd.com>,
        Pablo Cascon Katchadourian <pabloc@xilinx.com>,
        Zhu Lingshan <lingshan.zhu@intel.com>,
        Laurent Vivier <lvivier@redhat.com>,
        Longpeng <longpeng2@huawei.com>,
        Dinan Gunawardena <dinang@xilinx.com>,
        Martin Petrus Hubertus Habets <martinh@xilinx.com>,
        Martin Porter <martinpo@xilinx.com>,
        Eli Cohen <elic@nvidia.com>, ecree.xilinx@gmail.com,
        Wu Zongyong <wuzongyong@linux.alibaba.com>,
        Stefano Garzarella <sgarzare@redhat.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Harpreet Singh Anand <hanand@xilinx.com>,
        Xie Yongji <xieyongji@bytedance.com>,
        Zhang Min <zhang.min9@zte.com.cn>
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On Wed, Jun 29, 2022 at 6:12 AM Jason Wang <jasowang@redhat.com> wrote:
>
> On Fri, Jun 24, 2022 at 12:08 AM Eugenio P=C3=A9rez <eperezma@redhat.com>=
 wrote:
> >
> > Userland knows if it can suspend the device or not by checking this fea=
ture
> > bit.
> >
> > It's only offered if the vdpa driver backend implements the suspend()
> > operation callback, and to offer it or userland to ack it if the backen=
d
> > does not offer that callback is an error.
> >
> > Signed-off-by: Eugenio P=C3=A9rez <eperezma@redhat.com>
> > ---
> >  drivers/vhost/vdpa.c             | 16 +++++++++++++++-
> >  include/uapi/linux/vhost_types.h |  2 ++
> >  2 files changed, 17 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > index 23dcbfdfa13b..3d636e192061 100644
> > --- a/drivers/vhost/vdpa.c
> > +++ b/drivers/vhost/vdpa.c
> > @@ -347,6 +347,14 @@ static long vhost_vdpa_set_config(struct vhost_vdp=
a *v,
> >         return 0;
> >  }
> >
> > +static bool vhost_vdpa_can_suspend(const struct vhost_vdpa *v)
> > +{
> > +       struct vdpa_device *vdpa =3D v->vdpa;
> > +       const struct vdpa_config_ops *ops =3D vdpa->config;
> > +
> > +       return ops->suspend;
> > +}
> > +
> >  static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *=
featurep)
> >  {
> >         struct vdpa_device *vdpa =3D v->vdpa;
> > @@ -577,7 +585,11 @@ static long vhost_vdpa_unlocked_ioctl(struct file =
*filep,
> >         if (cmd =3D=3D VHOST_SET_BACKEND_FEATURES) {
> >                 if (copy_from_user(&features, featurep, sizeof(features=
)))
> >                         return -EFAULT;
> > -               if (features & ~VHOST_VDPA_BACKEND_FEATURES)
> > +               if (features & ~(VHOST_VDPA_BACKEND_FEATURES |
> > +                                BIT_ULL(VHOST_BACKEND_F_SUSPEND)))
> > +                       return -EOPNOTSUPP;
> > +               if ((features & BIT_ULL(VHOST_BACKEND_F_SUSPEND)) &&
> > +                    !vhost_vdpa_can_suspend(v))
>
> Do we need to advertise this to the management?
>

Not sure if I follow, the feature bit is not exposed if the backend
cannot suspend.

Thanks!

> Thanks
>
> >                         return -EOPNOTSUPP;
> >                 vhost_set_backend_features(&v->vdev, features);
> >                 return 0;
> > @@ -628,6 +640,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *=
filep,
> >                 break;
> >         case VHOST_GET_BACKEND_FEATURES:
> >                 features =3D VHOST_VDPA_BACKEND_FEATURES;
> > +               if (vhost_vdpa_can_suspend(v))
> > +                       features |=3D BIT_ULL(VHOST_BACKEND_F_SUSPEND);
> >                 if (copy_to_user(featurep, &features, sizeof(features))=
)
> >                         r =3D -EFAULT;
> >                 break;
> > diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhos=
t_types.h
> > index 634cee485abb..1bdd6e363f4c 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
> > +/* Device can be suspended */
> > +#define VHOST_BACKEND_F_SUSPEND  0x4
> >
> >  #endif
> > --
> > 2.31.1
> >
>