RE: [PATCH v3 2/4] vhost-vdpa: introduce STOP backend feature bit

["Dawar, Gautam" <gautam.dawar@amd.com>]

[AMD Official Use Only - General]

-----Original Message-----
From: Eugenio Pérez <eperezma@redhat.com>
Sent: Wednesday, May 25, 2022 4:29 PM
To: Michael S. Tsirkin <mst@redhat.com>; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; kvm@vger.kernel.org; virtualization@lists.linux-foundation.org; Jason Wang <jasowang@redhat.com>
Cc: Zhu Lingshan <lingshan.zhu@intel.com>; martinh@xilinx.com; Stefano Garzarella <sgarzare@redhat.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; Christophe JAILLET <christophe.jaillet@wanadoo.fr>; Xie Yongji <xieyongji@bytedance.com>; Dawar, Gautam <gautam.dawar@amd.com>; lulu@redhat.com; martinpo@xilinx.com; pabloc@xilinx.com; Longpeng <longpeng2@huawei.com>; Piotr.Uminski@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() operation callback, and try to set it if the backend does not offer that callback is an error.

Signed-off-by: Eugenio Pérez <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 1f1d1c425573..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 = v->vdpa;
+       const struct vdpa_config_ops *ops = vdpa->config;
+
+       return ops->stop;
[GD>>] Would it be better to explicitly return a bool to match the return type?
+}
+
 static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)  {
        struct vdpa_device *vdpa = v->vdpa; @@ -575,7 +583,11 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
        if (cmd == 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 *filep,
                break;
        case VHOST_GET_BACKEND_FEATURES:
                features = VHOST_VDPA_BACKEND_FEATURES;
+               if (vhost_vdpa_can_stop(v))
+                       features |= BIT_ULL(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
--
2.27.0