net/smc: bpf: Introduce generic hook for handshake flow

The introduction of IPPROTO_SMC enables eBPF programs to determine
whether to use SMC based on the context of socket creation, such as
network namespaces, PID and comm name, etc.

As a subsequent enhancement, to introduce a new generic hook that
allows decisions on whether to use SMC or not at runtime, including
but not limited to local/remote IP address or ports.

User can write their own implememtion via bpf_struct_ops now to choose
whether to use SMC or not before TCP 3rd handshake to be comleted.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Link: https://patch.msgid.link/20251107035632.115950-3-alibuda@linux.alibaba.com

1 files changed, 91 insertions, 0 deletions

diff --git a/net/smc/smc_sysctl.c b/net/smc/smc_sysctl.c
index 7b2471904d04..b1efed546243 100644
--- a/net/smc/smc_sysctl.c
+++ b/net/smc/smc_sysctl.c
@@ -12,12 +12,14 @@
 
 #include <linux/init.h>
 #include <linux/sysctl.h>
+#include <linux/bpf.h>
 #include <net/net_namespace.h>
 
 #include "smc.h"
 #include "smc_core.h"
 #include "smc_llc.h"
 #include "smc_sysctl.h"
+#include "smc_hs_bpf.h"
 
 static int min_sndbuf = SMC_BUF_MIN_SIZE;
 static int min_rcvbuf = SMC_BUF_MIN_SIZE;
@@ -32,6 +34,69 @@ static int conns_per_lgr_max = SMC_CONN_PER_LGR_MAX;
 static unsigned int smcr_max_wr_min = 2;
 static unsigned int smcr_max_wr_max = 2048;
 
+#if IS_ENABLED(CONFIG_SMC_HS_CTRL_BPF)
+static int smc_net_replace_smc_hs_ctrl(struct net *net, const char *name)
+{
+	struct smc_hs_ctrl *ctrl = NULL;
+
+	rcu_read_lock();
+	/* null or empty name ask to clear current ctrl */
+	if (name && name[0]) {
+		ctrl = smc_hs_ctrl_find_by_name(name);
+		if (!ctrl) {
+			rcu_read_unlock();
+			return -EINVAL;
+		}
+		/* no change, just return */
+		if (ctrl == rcu_dereference(net->smc.hs_ctrl)) {
+			rcu_read_unlock();
+			return 0;
+		}
+		if (!bpf_try_module_get(ctrl, ctrl->owner)) {
+			rcu_read_unlock();
+			return -EBUSY;
+		}
+	}
+	/* xhcg old ctrl with the new one atomically */
+	ctrl = unrcu_pointer(xchg(&net->smc.hs_ctrl, RCU_INITIALIZER(ctrl)));
+	/* release old ctrl */
+	if (ctrl)
+		bpf_module_put(ctrl, ctrl->owner);
+
+	rcu_read_unlock();
+	return 0;
+}
+
+static int proc_smc_hs_ctrl(const struct ctl_table *ctl, int write,
+			    void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct net *net = container_of(ctl->data, struct net, smc.hs_ctrl);
+	char val[SMC_HS_CTRL_NAME_MAX];
+	const struct ctl_table tbl = {
+		.data = val,
+		.maxlen = SMC_HS_CTRL_NAME_MAX,
+	};
+	struct smc_hs_ctrl *ctrl;
+	int ret;
+
+	rcu_read_lock();
+	ctrl = rcu_dereference(net->smc.hs_ctrl);
+	if (ctrl)
+		memcpy(val, ctrl->name, sizeof(ctrl->name));
+	else
+		val[0] = '\0';
+	rcu_read_unlock();
+
+	ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
+	if (ret)
+		return ret;
+
+	if (write)
+		ret = smc_net_replace_smc_hs_ctrl(net, val);
+	return ret;
+}
+#endif /* CONFIG_SMC_HS_CTRL_BPF */
+
 static struct ctl_table smc_table[] = {
 	{
 		.procname       = "autocorking_size",
@@ -119,6 +184,15 @@ static struct ctl_table smc_table[] = {
 		.extra1		= &smcr_max_wr_min,
 		.extra2		= &smcr_max_wr_max,
 	},
+#if IS_ENABLED(CONFIG_SMC_HS_CTRL_BPF)
+	{
+		.procname	= "hs_ctrl",
+		.data		= &init_net.smc.hs_ctrl,
+		.mode		= 0644,
+		.maxlen		= SMC_HS_CTRL_NAME_MAX,
+		.proc_handler	= proc_smc_hs_ctrl,
+	},
+#endif /* CONFIG_SMC_HS_CTRL_BPF */
 };
 
 int __net_init smc_sysctl_net_init(struct net *net)
@@ -129,6 +203,16 @@ int __net_init smc_sysctl_net_init(struct net *net)
 	table = smc_table;
 	if (!net_eq(net, &init_net)) {
 		int i;
+#if IS_ENABLED(CONFIG_SMC_HS_CTRL_BPF)
+		struct smc_hs_ctrl *ctrl;
+
+		rcu_read_lock();
+		ctrl = rcu_dereference(init_net.smc.hs_ctrl);
+		if (ctrl && ctrl->flags & SMC_HS_CTRL_FLAG_INHERITABLE &&
+		    bpf_try_module_get(ctrl, ctrl->owner))
+			rcu_assign_pointer(net->smc.hs_ctrl, ctrl);
+		rcu_read_unlock();
+#endif /* CONFIG_SMC_HS_CTRL_BPF */
 
 		table = kmemdup(table, sizeof(smc_table), GFP_KERNEL);
 		if (!table)
@@ -161,6 +245,9 @@ err_reg:
 	if (!net_eq(net, &init_net))
 		kfree(table);
 err_alloc:
+#if IS_ENABLED(CONFIG_SMC_HS_CTRL_BPF)
+	smc_net_replace_smc_hs_ctrl(net, NULL);
+#endif /* CONFIG_SMC_HS_CTRL_BPF */
 	return -ENOMEM;
 }
 
@@ -170,6 +257,10 @@ void __net_exit smc_sysctl_net_exit(struct net *net)
 
 	table = net->smc.smc_hdr->ctl_table_arg;
 	unregister_net_sysctl_table(net->smc.smc_hdr);
+#if IS_ENABLED(CONFIG_SMC_HS_CTRL_BPF)
+	smc_net_replace_smc_hs_ctrl(net, NULL);
+#endif /* CONFIG_SMC_HS_CTRL_BPF */
+
 	if (!net_eq(net, &init_net))
 		kfree(table);
 }