vhost-vdpa: support get/set backend features

This patch makes userspace can get and set backend features to
vhost-vdpa.
Signed-off-by: Cindy Lu <lulu@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20200804162048.22587-4-eli@mellanox.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vdpa.c

@@ -26,6 +26,10 @@
 
 #include "vhost.h"
 
+enum {
+	VHOST_VDPA_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
+};
+
 /* Currently, only network backend w/o multiqueue is supported. */
 #define VHOST_VDPA_VQ_MAX	2
 
@@ -347,6 +351,8 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 	struct vdpa_callback cb;
 	struct vhost_virtqueue *vq;
 	struct vhost_vring_state s;
+	u64 __user *featurep = argp;
+	u64 features;
 	u32 idx;
 	long r;
 
@@ -369,6 +375,18 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 	case VHOST_GET_VRING_BASE:
 		vq->last_avail_idx = ops->get_vq_state(v->vdpa, idx);
 		break;
+	case VHOST_GET_BACKEND_FEATURES:
+		features = VHOST_VDPA_BACKEND_FEATURES;
+		if (copy_to_user(featurep, &features, sizeof(features)))
+			return -EFAULT;
+		return 0;
+	case VHOST_SET_BACKEND_FEATURES:
+		if (copy_from_user(&features, featurep, sizeof(features)))
+			return -EFAULT;
+		if (features & ~VHOST_VDPA_BACKEND_FEATURES)
+			return -EOPNOTSUPP;
+		vhost_set_backend_features(&v->vdev, features);
+		return 0;
 	}
 
 	r = vhost_vring_ioctl(&v->vdev, cmd, argp);