Merge branch 'net-introduce-rps_default_mask'

Paolo Abeni says:

====================
net: introduce rps_default_mask

Real-time setups try hard to ensure proper isolation between time
critical applications and e.g. network processing performed by the
network stack in softirq and RPS is used to move the softirq
activity away from the isolated core.

If the network configuration is dynamic, with netns and devices
routinely created at run-time, enforcing the correct RPS setting
on each newly created device allowing to transient bad configuration
became complex.

Additionally, when multi-queue devices are involved, configuring rps
in user-space on each queue easily becomes very expensive, e.g.
some setups use veths with per cpu queues.

These series try to address the above, introducing a new
sysctl knob: rps_default_mask. The new sysctl entry allows
configuring a netns-wide RPS mask, to be enforced since receive
queue creation time without any fourther per device configuration
required.

Additionally, a simple self-test is introduced to check the
rps_default_mask behavior.
====================

Link: https://lore.kernel.org/r/cover.1675789134.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 114 insertions, 48 deletions

diff --git a/net/core/dev.h b/net/core/dev.h
index a065b7571441..e075e198092c 100644
--- a/net/core/dev.h
+++ b/net/core/dev.h
@@ -9,6 +9,7 @@ struct net_device;
 struct netdev_bpf;
 struct netdev_phys_item_id;
 struct netlink_ext_ack;
+struct cpumask;
 
 /* Random bits of netdevice that don't need to be exposed */
 #define FLOW_LIMIT_HISTORY	(1 << 7)  /* must be ^2 and !overflow buckets */
@@ -134,4 +135,5 @@ static inline void netif_set_gro_ipv4_max_size(struct net_device *dev,
 	WRITE_ONCE(dev->gro_ipv4_max_size, size);
 }
 
+int rps_cpumask_housekeeping(struct cpumask *mask);
 #endif
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index ca55dd747d6c..4b361ac6a252 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -831,42 +831,18 @@ static ssize_t show_rps_map(struct netdev_rx_queue *queue, char *buf)
 	return len < PAGE_SIZE ? len : -EINVAL;
 }
 
-static ssize_t store_rps_map(struct netdev_rx_queue *queue,
-			     const char *buf, size_t len)
+static int netdev_rx_queue_set_rps_mask(struct netdev_rx_queue *queue,
+					cpumask_var_t mask)
 {
-	struct rps_map *old_map, *map;
-	cpumask_var_t mask;
-	int err, cpu, i;
 	static DEFINE_MUTEX(rps_map_mutex);
-
-	if (!capable(CAP_NET_ADMIN))
-		return -EPERM;
-
-	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
-		return -ENOMEM;
-
-	err = bitmap_parse(buf, len, cpumask_bits(mask), nr_cpumask_bits);
-	if (err) {
-		free_cpumask_var(mask);
-		return err;
-	}
-
-	if (!cpumask_empty(mask)) {
-		cpumask_and(mask, mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
-		cpumask_and(mask, mask, housekeeping_cpumask(HK_TYPE_WQ));
-		if (cpumask_empty(mask)) {
-			free_cpumask_var(mask);
-			return -EINVAL;
-		}
-	}
+	struct rps_map *old_map, *map;
+	int cpu, i;
 
 	map = kzalloc(max_t(unsigned int,
 			    RPS_MAP_SIZE(cpumask_weight(mask)), L1_CACHE_BYTES),
 		      GFP_KERNEL);
-	if (!map) {
-		free_cpumask_var(mask);
+	if (!map)
 		return -ENOMEM;
-	}
 
 	i = 0;
 	for_each_cpu_and(cpu, mask, cpu_online_mask)
@@ -893,9 +869,45 @@ static ssize_t store_rps_map(struct netdev_rx_queue *queue,
 
 	if (old_map)
 		kfree_rcu(old_map, rcu);
+	return 0;
+}
 
+int rps_cpumask_housekeeping(struct cpumask *mask)
+{
+	if (!cpumask_empty(mask)) {
+		cpumask_and(mask, mask, housekeeping_cpumask(HK_TYPE_DOMAIN));
+		cpumask_and(mask, mask, housekeeping_cpumask(HK_TYPE_WQ));
+		if (cpumask_empty(mask))
+			return -EINVAL;
+	}
+	return 0;
+}
+
+static ssize_t store_rps_map(struct netdev_rx_queue *queue,
+			     const char *buf, size_t len)
+{
+	cpumask_var_t mask;
+	int err;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
+		return -ENOMEM;
+
+	err = bitmap_parse(buf, len, cpumask_bits(mask), nr_cpumask_bits);
+	if (err)
+		goto out;
+
+	err = rps_cpumask_housekeeping(mask);
+	if (err)
+		goto out;
+
+	err = netdev_rx_queue_set_rps_mask(queue, mask);
+
+out:
 	free_cpumask_var(mask);
-	return len;
+	return err ? : len;
 }
 
 static ssize_t show_rps_dev_flow_table_cnt(struct netdev_rx_queue *queue,
@@ -1071,6 +1083,13 @@ static int rx_queue_add_kobject(struct net_device *dev, int index)
 			goto err;
 	}
 
+#if IS_ENABLED(CONFIG_RPS) && IS_ENABLED(CONFIG_SYSCTL)
+	if (!cpumask_empty(&rps_default_mask)) {
+		error = netdev_rx_queue_set_rps_mask(queue, &rps_default_mask);
+		if (error)
+			goto err;
+	}
+#endif
 	kobject_uevent(kobj, KOBJ_ADD);
 
 	return error;
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index e7b98162c632..7130e6d9e263 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -16,6 +16,7 @@
 #include <linux/vmalloc.h>
 #include <linux/init.h>
 #include <linux/slab.h>
+#include <linux/sched/isolation.h>
 
 #include <net/ip.h>
 #include <net/sock.h>
@@ -45,7 +46,59 @@ EXPORT_SYMBOL(sysctl_fb_tunnels_only_for_init_net);
 int sysctl_devconf_inherit_init_net __read_mostly;
 EXPORT_SYMBOL(sysctl_devconf_inherit_init_net);
 
+#if IS_ENABLED(CONFIG_NET_FLOW_LIMIT) || IS_ENABLED(CONFIG_RPS)
+static void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos,
+			 struct cpumask *mask)
+{
+	char kbuf[128];
+	int len;
+
+	if (*ppos || !*lenp) {
+		*lenp = 0;
+		return;
+	}
+
+	len = min(sizeof(kbuf) - 1, *lenp);
+	len = scnprintf(kbuf, len, "%*pb", cpumask_pr_args(mask));
+	if (!len) {
+		*lenp = 0;
+		return;
+	}
+
+	if (len < *lenp)
+		kbuf[len++] = '\n';
+	memcpy(buffer, kbuf, len);
+	*lenp = len;
+	*ppos += len;
+}
+#endif
+
 #ifdef CONFIG_RPS
+struct cpumask rps_default_mask;
+
+static int rps_default_mask_sysctl(struct ctl_table *table, int write,
+				   void *buffer, size_t *lenp, loff_t *ppos)
+{
+	int err = 0;
+
+	rtnl_lock();
+	if (write) {
+		err = cpumask_parse(buffer, &rps_default_mask);
+		if (err)
+			goto done;
+
+		err = rps_cpumask_housekeeping(&rps_default_mask);
+		if (err)
+			goto done;
+	} else {
+		dump_cpumask(buffer, lenp, ppos, &rps_default_mask);
+	}
+
+done:
+	rtnl_unlock();
+	return err;
+}
+
 static int rps_sock_flow_sysctl(struct ctl_table *table, int write,
 				void *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -155,13 +208,6 @@ static int flow_limit_cpu_sysctl(struct ctl_table *table, int write,
 write_unlock:
 		mutex_unlock(&flow_limit_update_mutex);
 	} else {
-		char kbuf[128];
-
-		if (*ppos || !*lenp) {
-			*lenp = 0;
-			goto done;
-		}
-
 		cpumask_clear(mask);
 		rcu_read_lock();
 		for_each_possible_cpu(i) {
@@ -171,17 +217,7 @@ write_unlock:
 		}
 		rcu_read_unlock();
 
-		len = min(sizeof(kbuf) - 1, *lenp);
-		len = scnprintf(kbuf, len, "%*pb", cpumask_pr_args(mask));
-		if (!len) {
-			*lenp = 0;
-			goto done;
-		}
-		if (len < *lenp)
-			kbuf[len++] = '\n';
-		memcpy(buffer, kbuf, len);
-		*lenp = len;
-		*ppos += len;
+		dump_cpumask(buffer, lenp, ppos, mask);
 	}
 
 done:
@@ -472,6 +508,11 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0644,
 		.proc_handler	= rps_sock_flow_sysctl
 	},
+	{
+		.procname	= "rps_default_mask",
+		.mode		= 0644,
+		.proc_handler	= rps_default_mask_sysctl
+	},
 #endif
 #ifdef CONFIG_NET_FLOW_LIMIT
 	{
@@ -675,6 +716,10 @@ static __net_initdata struct pernet_operations sysctl_core_ops = {
 
 static __init int sysctl_core_init(void)
 {
+#if IS_ENABLED(CONFIG_RPS)
+	cpumask_copy(&rps_default_mask, cpu_none_mask);
+#endif
+
 	register_net_sysctl(&init_net, "net/core", net_core_table);
 	return register_pernet_subsys(&sysctl_core_ops);
 }