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From:   Eugenio Perez Martin <eperezma@redhat.com>
Date:   Thu, 26 May 2022 10:57:03 +0200
Message-ID: <CAJaqyWc9_ErCg4whLKrjNyP5z2DZno-LJm7PN=-9uk7PUT4fJw@mail.gmail.com>
Subject: Re: [PATCH v3 2/4] vhost-vdpa: introduce STOP backend feature bit
To:     "Dawar, Gautam" <gautam.dawar@amd.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "virtualization@lists.linux-foundation.org" 
        <virtualization@lists.linux-foundation.org>,
        Jason Wang <jasowang@redhat.com>,
        Zhu Lingshan <lingshan.zhu@intel.com>,
        "martinh@xilinx.com" <martinh@xilinx.com>,
        Stefano Garzarella <sgarzare@redhat.com>,
        "ecree.xilinx@gmail.com" <ecree.xilinx@gmail.com>,
        Eli Cohen <elic@nvidia.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Parav Pandit <parav@nvidia.com>,
        Wu Zongyong <wuzongyong@linux.alibaba.com>,
        "dinang@xilinx.com" <dinang@xilinx.com>,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Xie Yongji <xieyongji@bytedance.com>,
        "lulu@redhat.com" <lulu@redhat.com>,
        "martinpo@xilinx.com" <martinpo@xilinx.com>,
        "pabloc@xilinx.com" <pabloc@xilinx.com>,
        Longpeng <longpeng2@huawei.com>,
        "Piotr.Uminski@intel.com" <Piotr.Uminski@intel.com>,
        "Kamde, Tanuj" <tanuj.kamde@amd.com>,
        Si-Wei Liu <si-wei.liu@oracle.com>,
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        "lvivier@redhat.com" <lvivier@redhat.com>,
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On Wed, May 25, 2022 at 1:23 PM Dawar, Gautam <gautam.dawar@amd.com> wrote:
>
> [AMD Official Use Only - General]
>
> -----Original Message-----
> From: Eugenio P=C3=A9rez <eperezma@redhat.com>
> Sent: Wednesday, May 25, 2022 4:29 PM
> To: Michael S. Tsirkin <mst@redhat.com>; netdev@vger.kernel.org; linux-ke=
rnel@vger.kernel.org; kvm@vger.kernel.org; virtualization@lists.linux-found=
ation.org; Jason Wang <jasowang@redhat.com>
> Cc: Zhu Lingshan <lingshan.zhu@intel.com>; martinh@xilinx.com; Stefano Ga=
rzarella <sgarzare@redhat.com>; ecree.xilinx@gmail.com; Eli Cohen <elic@nvi=
dia.com>; Dan Carpenter <dan.carpenter@oracle.com>; Parav Pandit <parav@nvi=
dia.com>; Wu Zongyong <wuzongyong@linux.alibaba.com>; dinang@xilinx.com; Ch=
ristophe JAILLET <christophe.jaillet@wanadoo.fr>; Xie Yongji <xieyongji@byt=
edance.com>; Dawar, Gautam <gautam.dawar@amd.com>; lulu@redhat.com; martinp=
o@xilinx.com; pabloc@xilinx.com; Longpeng <longpeng2@huawei.com>; Piotr.Umi=
nski@intel.com; Kamde, Tanuj <tanuj.kamde@amd.com>; Si-Wei Liu <si-wei.liu@=
oracle.com>; habetsm.xilinx@gmail.com; lvivier@redhat.com; Zhang Min <zhang=
.min9@zte.com.cn>; hanand@xilinx.com
> Subject: [PATCH v3 2/4] vhost-vdpa: introduce STOP backend feature bit
>
> [CAUTION: External Email]
>
> 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() operat=
ion callback, and try to set it if the backend 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 1f1d1c4255=
73..32713db5831d 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 =3D v->vdpa;
> +       const struct vdpa_config_ops *ops =3D vdpa->config;
> +
> +       return ops->stop;
> [GD>>] Would it be better to explicitly return a bool to match the return=
 type?

I'm not sure about the kernel code style regarding that casting. Maybe
it's better to return !!ops->stop here. The macros likely and unlikely
do that.

Thanks!

> +}
> +
>  static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *fe=
aturep)  {
>         struct vdpa_device *vdpa =3D v->vdpa; @@ -575,7 +583,11 @@ 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_STOP)))
> +                       return -EOPNOTSUPP;
> +               if ((features & BIT_ULL(VHOST_BACKEND_F_STOP)) &&
> +                    !vhost_vdpa_can_stop(v))
>                         return -EOPNOTSUPP;
>                 vhost_set_backend_features(&v->vdev, features);
>                 return 0;
> @@ -624,6 +636,8 @@ static long vhost_vdpa_unlocked_ioctl(struct file *fi=
lep,
>                 break;
>         case VHOST_GET_BACKEND_FEATURES:
>                 features =3D VHOST_VDPA_BACKEND_FEATURES;
> +               if (vhost_vdpa_can_stop(v))
> +                       features |=3D BIT_ULL(VHOST_BACKEND_F_STOP);
>                 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/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
> --
> 2.27.0
>