net: move mp dev config validation to __net_mp_open_rxq()

devmem code performs a number of safety checks to avoid having
to reimplement all of them in the drivers. Move those to
__net_mp_open_rxq() and reuse that function for binding to make
sure that io_uring ZC also benefits from them.

While at it rename the queue ID variable to rxq_idx in
__net_mp_open_rxq(), we touch most of the relevant lines.

The XArray insertion is reordered after the netdev_rx_queue_restart()
call, otherwise we'd need to duplicate the queue index check
or risk inserting an invalid pointer. The XArray allocation
failures should be extremely rare.

Reviewed-by: Mina Almasry <almasrymina@google.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Fixes: 6e18ed9 ("net: add helpers for setting a memory provider on an rx queue")
Link: https://patch.msgid.link/20250403013405.2827250-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

include/net/page_pool/memory_provider.h

@@ -6,6 +6,7 @@
 #include <net/page_pool/types.h>
 
 struct netdev_rx_queue;
+struct netlink_ext_ack;
 struct sk_buff;
 
 struct memory_provider_ops {
@@ -24,8 +25,13 @@ void net_mp_niov_clear_page_pool(struct net_iov *niov);
 
 int net_mp_open_rxq(struct net_device *dev, unsigned ifq_idx,
 		    struct pp_memory_provider_params *p);
+int __net_mp_open_rxq(struct net_device *dev, unsigned int rxq_idx,
+		      const struct pp_memory_provider_params *p,
+		      struct netlink_ext_ack *extack);
 void net_mp_close_rxq(struct net_device *dev, unsigned ifq_idx,
 		      struct pp_memory_provider_params *old_p);
+void __net_mp_close_rxq(struct net_device *dev, unsigned int rxq_idx,
+			const struct pp_memory_provider_params *old_p);
 
 /**
   * net_mp_netmem_place_in_cache() - give a netmem to a page pool

net/core/devmem.c

@@ -8,7 +8,6 @@
  */
 
 #include <linux/dma-buf.h>
-#include <linux/ethtool_netlink.h>
 #include <linux/genalloc.h>
 #include <linux/mm.h>
 #include <linux/netdevice.h>
@@ -143,57 +142,28 @@ int net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
 				    struct net_devmem_dmabuf_binding *binding,
 				    struct netlink_ext_ack *extack)
 {
+	struct pp_memory_provider_params mp_params = {
+		.mp_priv	= binding,
+		.mp_ops		= &dmabuf_devmem_ops,
+	};
 	struct netdev_rx_queue *rxq;
 	u32 xa_idx;
 	int err;
 
-	if (rxq_idx >= dev->real_num_rx_queues) {
-		NL_SET_ERR_MSG(extack, "rx queue index out of range");
-		return -ERANGE;
-	}
-
-	if (dev->cfg->hds_config != ETHTOOL_TCP_DATA_SPLIT_ENABLED) {
-		NL_SET_ERR_MSG(extack, "tcp-data-split is disabled");
-		return -EINVAL;
-	}
-
-	if (dev->cfg->hds_thresh) {
-		NL_SET_ERR_MSG(extack, "hds-thresh is not zero");
-		return -EINVAL;
-	}
+	err = __net_mp_open_rxq(dev, rxq_idx, &mp_params, extack);
+	if (err)
+		return err;
 
 	rxq = __netif_get_rx_queue(dev, rxq_idx);
-	if (rxq->mp_params.mp_ops) {
-		NL_SET_ERR_MSG(extack, "designated queue already memory provider bound");
-		return -EEXIST;
-	}
-
-#ifdef CONFIG_XDP_SOCKETS
-	if (rxq->pool) {
-		NL_SET_ERR_MSG(extack, "designated queue already in use by AF_XDP");
-		return -EBUSY;
-	}
-#endif
-
 	err = xa_alloc(&binding->bound_rxqs, &xa_idx, rxq, xa_limit_32b,
 		       GFP_KERNEL);
 	if (err)
-		return err;
-
-	rxq->mp_params.mp_priv = binding;
-	rxq->mp_params.mp_ops = &dmabuf_devmem_ops;
-
-	err = netdev_rx_queue_restart(dev, rxq_idx);
-	if (err)
-		goto err_xa_erase;
+		goto err_close_rxq;
 
 	return 0;
 
-err_xa_erase:
-	rxq->mp_params.mp_priv = NULL;
-	rxq->mp_params.mp_ops = NULL;
-	xa_erase(&binding->bound_rxqs, xa_idx);
-
+err_close_rxq:
+	__net_mp_close_rxq(dev, rxq_idx, &mp_params);
 	return err;
 }
 

net/core/netdev-genl.c

@@ -874,12 +874,6 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
 		goto err_unlock;
 	}
 
-	if (dev_xdp_prog_count(netdev)) {
-		NL_SET_ERR_MSG(info->extack, "unable to bind dmabuf to device with XDP program attached");
-		err = -EEXIST;
-		goto err_unlock;
-	}
-
 	binding = net_devmem_bind_dmabuf(netdev, dmabuf_fd, info->extack);
 	if (IS_ERR(binding)) {
 		err = PTR_ERR(binding);

net/core/netdev_rx_queue.c

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#include <linux/ethtool_netlink.h>
 #include <linux/netdevice.h>
 #include <net/netdev_lock.h>
 #include <net/netdev_queues.h>
@@ -86,45 +87,71 @@ int netdev_rx_queue_restart(struct net_device *dev, unsigned int rxq_idx)
 }
 EXPORT_SYMBOL_NS_GPL(netdev_rx_queue_restart, "NETDEV_INTERNAL");
 
-static int __net_mp_open_rxq(struct net_device *dev, unsigned ifq_idx,
-			     struct pp_memory_provider_params *p)
+int __net_mp_open_rxq(struct net_device *dev, unsigned int rxq_idx,
+		      const struct pp_memory_provider_params *p,
+		      struct netlink_ext_ack *extack)
 {
 	struct netdev_rx_queue *rxq;
 	int ret;
 
 	if (!netdev_need_ops_lock(dev))
 		return -EOPNOTSUPP;
 
-	if (ifq_idx >= dev->real_num_rx_queues)
+	if (rxq_idx >= dev->real_num_rx_queues)
 		return -EINVAL;
-	ifq_idx = array_index_nospec(ifq_idx, dev->real_num_rx_queues);
+	rxq_idx = array_index_nospec(rxq_idx, dev->real_num_rx_queues);
 
-	rxq = __netif_get_rx_queue(dev, ifq_idx);
-	if (rxq->mp_params.mp_ops)
+	if (rxq_idx >= dev->real_num_rx_queues) {
+		NL_SET_ERR_MSG(extack, "rx queue index out of range");
+		return -ERANGE;
+	}
+	if (dev->cfg->hds_config != ETHTOOL_TCP_DATA_SPLIT_ENABLED) {
+		NL_SET_ERR_MSG(extack, "tcp-data-split is disabled");
+		return -EINVAL;
+	}
+	if (dev->cfg->hds_thresh) {
+		NL_SET_ERR_MSG(extack, "hds-thresh is not zero");
+		return -EINVAL;
+	}
+	if (dev_xdp_prog_count(dev)) {
+		NL_SET_ERR_MSG(extack, "unable to custom memory provider to device with XDP program attached");
 		return -EEXIST;
+	}
+
+	rxq = __netif_get_rx_queue(dev, rxq_idx);
+	if (rxq->mp_params.mp_ops) {
+		NL_SET_ERR_MSG(extack, "designated queue already memory provider bound");
+		return -EEXIST;
+	}
+#ifdef CONFIG_XDP_SOCKETS
+	if (rxq->pool) {
+		NL_SET_ERR_MSG(extack, "designated queue already in use by AF_XDP");
+		return -EBUSY;
+	}
+#endif
 
 	rxq->mp_params = *p;
-	ret = netdev_rx_queue_restart(dev, ifq_idx);
+	ret = netdev_rx_queue_restart(dev, rxq_idx);
 	if (ret) {
 		rxq->mp_params.mp_ops = NULL;
 		rxq->mp_params.mp_priv = NULL;
 	}
 	return ret;
 }
 
-int net_mp_open_rxq(struct net_device *dev, unsigned ifq_idx,
+int net_mp_open_rxq(struct net_device *dev, unsigned int rxq_idx,
 		    struct pp_memory_provider_params *p)
 {
 	int ret;
 
 	netdev_lock(dev);
-	ret = __net_mp_open_rxq(dev, ifq_idx, p);
+	ret = __net_mp_open_rxq(dev, rxq_idx, p, NULL);
 	netdev_unlock(dev);
 	return ret;
 }
 
-static void __net_mp_close_rxq(struct net_device *dev, unsigned ifq_idx,
-			      struct pp_memory_provider_params *old_p)
+void __net_mp_close_rxq(struct net_device *dev, unsigned int ifq_idx,
+			const struct pp_memory_provider_params *old_p)
 {
 	struct netdev_rx_queue *rxq;