net: add queue config validation callback

I imagine (tm) that as the number of per-queue configuration
options grows some of them may conflict for certain drivers.
While the drivers can obviously do all the validation locally
doing so is fairly inconvenient as the config is fed to drivers
piecemeal via different ops (for different params and NIC-wide
vs per-queue).

Add a centralized callback for validating the queue config
in queue ops. The callback gets invoked before memory provider
is installed, and in the future should also be called when ring
params are modified.

The validation is done after each layer of configuration.
Since we can't fail MP un-binding we must make sure that
the config is valid both before and after MP overrides are
applied. This is moot for now since the set of MP and device
configs are disjoint. It will matter significantly in the future,
so adding it now so that we don't forget..

Link: https://patch.msgid.link/20260122005113.2476634-6-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 66 insertions, 14 deletions

diff --git a/net/core/dev.h b/net/core/dev.h
index da18536cbd35..98793a738f43 100644
--- a/net/core/dev.h
+++ b/net/core/dev.h
@@ -10,6 +10,7 @@
 
 struct net;
 struct netlink_ext_ack;
+struct netdev_queue_config;
 struct cpumask;
 
 /* Random bits of netdevice that don't need to be exposed */
@@ -91,6 +92,10 @@ extern struct rw_semaphore dev_addr_sem;
 extern struct list_head net_todo_list;
 void netdev_run_todo(void);
 
+int netdev_queue_config_validate(struct net_device *dev, int rxq_idx,
+				 struct netdev_queue_config *qcfg,
+				 struct netlink_ext_ack *extack);
+
 /* netdev management, shared between various uAPI entry points */
 struct netdev_name_node {
 	struct hlist_node hlist;
diff --git a/net/core/netdev_config.c b/net/core/netdev_config.c
index 48f763446506..f14af365d5cd 100644
--- a/net/core/netdev_config.c
+++ b/net/core/netdev_config.c
@@ -4,6 +4,50 @@
 #include <net/netdev_queues.h>
 #include <net/netdev_rx_queue.h>
 
+#include "dev.h"
+
+static int netdev_nop_validate_qcfg(struct net_device *dev,
+				    struct netdev_queue_config *qcfg,
+				    struct netlink_ext_ack *extack)
+{
+	return 0;
+}
+
+static int __netdev_queue_config(struct net_device *dev, int rxq_idx,
+				 struct netdev_queue_config *qcfg,
+				 struct netlink_ext_ack *extack,
+				 bool validate)
+{
+	int (*validate_cb)(struct net_device *dev,
+			   struct netdev_queue_config *qcfg,
+			   struct netlink_ext_ack *extack);
+	struct pp_memory_provider_params *mpp;
+	int err;
+
+	validate_cb = netdev_nop_validate_qcfg;
+	if (validate && dev->queue_mgmt_ops->ndo_validate_qcfg)
+		validate_cb = dev->queue_mgmt_ops->ndo_validate_qcfg;
+
+	memset(qcfg, 0, sizeof(*qcfg));
+
+	/* Get defaults from the driver, in case user config not set */
+	if (dev->queue_mgmt_ops->ndo_default_qcfg)
+		dev->queue_mgmt_ops->ndo_default_qcfg(dev, qcfg);
+	err = validate_cb(dev, qcfg, extack);
+	if (err)
+		return err;
+
+	/* Apply MP overrides */
+	mpp = &__netif_get_rx_queue(dev, rxq_idx)->mp_params;
+	if (mpp->rx_page_size)
+		qcfg->rx_page_size = mpp->rx_page_size;
+	err = validate_cb(dev, qcfg, extack);
+	if (err)
+		return err;
+
+	return 0;
+}
+
 /**
  * netdev_queue_config() - get configuration for a given queue
  * @dev:      net_device instance
@@ -22,17 +66,13 @@
 void netdev_queue_config(struct net_device *dev, int rxq_idx,
 			 struct netdev_queue_config *qcfg)
 {
-	struct pp_memory_provider_params *mpp;
-
-	memset(qcfg, 0, sizeof(*qcfg));
-
-	/* Get defaults from the driver, in case user config not set */
-	if (dev->queue_mgmt_ops->ndo_default_qcfg)
-		dev->queue_mgmt_ops->ndo_default_qcfg(dev, qcfg);
-
-	/* Apply MP overrides */
-	mpp = &__netif_get_rx_queue(dev, rxq_idx)->mp_params;
-	if (mpp->rx_page_size)
-		qcfg->rx_page_size = mpp->rx_page_size;
+	__netdev_queue_config(dev, rxq_idx, qcfg, NULL, false);
 }
 EXPORT_SYMBOL(netdev_queue_config);
+
+int netdev_queue_config_validate(struct net_device *dev, int rxq_idx,
+				 struct netdev_queue_config *qcfg,
+				 struct netlink_ext_ack *extack)
+{
+	return __netdev_queue_config(dev, rxq_idx, qcfg, extack, true);
+}
diff --git a/net/core/netdev_rx_queue.c b/net/core/netdev_rx_queue.c
index 72374930699a..668a90658f25 100644
--- a/net/core/netdev_rx_queue.c
+++ b/net/core/netdev_rx_queue.c
@@ -7,6 +7,7 @@
 #include <net/netdev_rx_queue.h>
 #include <net/page_pool/memory_provider.h>
 
+#include "dev.h"
 #include "page_pool_priv.h"
 
 /* See also page_pool_is_unreadable() */
@@ -156,12 +157,18 @@ int __net_mp_open_rxq(struct net_device *dev, unsigned int rxq_idx,
 
 	netdev_queue_config(dev, rxq_idx, &qcfg[0]);
 	rxq->mp_params = *p;
-	netdev_queue_config(dev, rxq_idx, &qcfg[1]);
+	ret = netdev_queue_config_validate(dev, rxq_idx, &qcfg[1], extack);
+	if (ret)
+		goto err_clear_mp;
 
 	ret = netdev_rx_queue_reconfig(dev, rxq_idx, &qcfg[0], &qcfg[1]);
 	if (ret)
-		memset(&rxq->mp_params, 0, sizeof(rxq->mp_params));
+		goto err_clear_mp;
+
+	return 0;
 
+err_clear_mp:
+	memset(&rxq->mp_params, 0, sizeof(rxq->mp_params));
 	return ret;
 }