vdpa: Allow to configure max data virtqueues

Add netlink support to configure the max virtqueue pairs for a device.
At least one pair is required. The maximum is dictated by the device.

Example:
$ vdpa dev add name vdpa-a mgmtdev auxiliary/mlx5_core.sf.1 max_vqp 4
Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20220105114646.577224-6-elic@nvidia.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vdpa/vdpa.c

@@ -404,7 +404,7 @@ static void vdpa_get_config_unlocked(struct vdpa_device *vdev,
 	 * If it does happen we assume a legacy guest.
 	 */
 	if (!vdev->features_valid)
-		vdpa_set_features(vdev, 0);
+		vdpa_set_features(vdev, 0, true);
 	ops->get_config(vdev, offset, buf, len);
 }
 
@@ -581,7 +581,8 @@ vdpa_nl_cmd_mgmtdev_get_dumpit(struct sk_buff *msg, struct netlink_callback *cb)
 }
 
 #define VDPA_DEV_NET_ATTRS_MASK ((1 << VDPA_ATTR_DEV_NET_CFG_MACADDR) | \
-				 (1 << VDPA_ATTR_DEV_NET_CFG_MTU))
+				 (1 << VDPA_ATTR_DEV_NET_CFG_MTU) | \
+				 (1 << VDPA_ATTR_DEV_NET_CFG_MAX_VQP))
 
 static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff *skb, struct genl_info *info)
 {
@@ -607,6 +608,16 @@ static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff *skb, struct genl_info *i
 			nla_get_u16(nl_attrs[VDPA_ATTR_DEV_NET_CFG_MTU]);
 		config.mask |= (1 << VDPA_ATTR_DEV_NET_CFG_MTU);
 	}
+	if (nl_attrs[VDPA_ATTR_DEV_NET_CFG_MAX_VQP]) {
+		config.net.max_vq_pairs =
+			nla_get_u16(nl_attrs[VDPA_ATTR_DEV_NET_CFG_MAX_VQP]);
+		if (!config.net.max_vq_pairs) {
+			NL_SET_ERR_MSG_MOD(info->extack,
+					   "At least one pair of VQs is required");
+			return -EINVAL;
+		}
+		config.mask |= BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MAX_VQP);
+	}
 
 	/* Skip checking capability if user didn't prefer to configure any
 	 * device networking attributes. It is likely that user might have used

drivers/vhost/vdpa.c

@@ -285,7 +285,7 @@ static long vhost_vdpa_set_features(struct vhost_vdpa *v, u64 __user *featurep)
 	if (copy_from_user(&features, featurep, sizeof(features)))
 		return -EFAULT;
 
-	if (vdpa_set_features(vdpa, features))
+	if (vdpa_set_features(vdpa, features, false))
 		return -EINVAL;
 
 	return 0;

drivers/virtio/virtio_vdpa.c

@@ -317,7 +317,7 @@ static int virtio_vdpa_finalize_features(struct virtio_device *vdev)
 	/* Give virtio_ring a chance to accept features. */
 	vring_transport_features(vdev);
 
-	return vdpa_set_features(vdpa, vdev->features);
+	return vdpa_set_features(vdpa, vdev->features, false);
 }
 
 static const char *virtio_vdpa_bus_name(struct virtio_device *vdev)

include/linux/vdpa.h

@@ -101,6 +101,7 @@ struct vdpa_dev_set_config {
 	struct {
 		u8 mac[ETH_ALEN];
 		u16 mtu;
+		u16 max_vq_pairs;
 	} net;
 	u64 mask;
 };
@@ -391,17 +392,29 @@ static inline struct device *vdpa_get_dma_dev(struct vdpa_device *vdev)
 static inline int vdpa_reset(struct vdpa_device *vdev)
 {
 	const struct vdpa_config_ops *ops = vdev->config;
+	int ret;
 
+	mutex_lock(&vdev->cf_mutex);
 	vdev->features_valid = false;
-	return ops->reset(vdev);
+	ret = ops->reset(vdev);
+	mutex_unlock(&vdev->cf_mutex);
+	return ret;
 }
 
-static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features)
+static inline int vdpa_set_features(struct vdpa_device *vdev, u64 features, bool locked)
 {
 	const struct vdpa_config_ops *ops = vdev->config;
+	int ret;
+
+	if (!locked)
+		mutex_lock(&vdev->cf_mutex);
 
 	vdev->features_valid = true;
-	return ops->set_driver_features(vdev, features);
+	ret = ops->set_driver_features(vdev, features);
+	if (!locked)
+		mutex_unlock(&vdev->cf_mutex);
+
+	return ret;
 }
 
 void vdpa_get_config(struct vdpa_device *vdev, unsigned int offset,