netfilter: nf_tables: avoid retpoline overhead for some ct expression calls

nft_ct expression cannot be made builtin to nf_tables without also
forcing the conntrack itself to be builtin.

However, this can be avoided by splitting retrieval of a few
selector keys that only need to access the nf_conn structure,
i.e. no function calls to nf_conntrack code.

Many rulesets start with something like
"ct status established,related accept"

With this change, this no longer requires an indirect call, which
gives about 1.8% more throughput with a simple conntrack-enabled
forwarding test (retpoline thunk used).

Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 56 insertions, 0 deletions

diff --git a/net/netfilter/nft_ct_fast.c b/net/netfilter/nft_ct_fast.c
new file mode 100644
index 00000000000000..89983b0613fa39
--- /dev/null
+++ b/net/netfilter/nft_ct_fast.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#if IS_ENABLED(CONFIG_NFT_CT)
+#include <linux/netfilter/nf_tables.h>
+#include <net/netfilter/nf_tables_core.h>
+#include <net/netfilter/nf_conntrack.h>
+
+void nft_ct_get_fast_eval(const struct nft_expr *expr,
+			  struct nft_regs *regs,
+			  const struct nft_pktinfo *pkt)
+{
+	const struct nft_ct *priv = nft_expr_priv(expr);
+	u32 *dest = &regs->data[priv->dreg];
+	enum ip_conntrack_info ctinfo;
+	const struct nf_conn *ct;
+	unsigned int state;
+
+	ct = nf_ct_get(pkt->skb, &ctinfo);
+	if (!ct) {
+		regs->verdict.code = NFT_BREAK;
+		return;
+	}
+
+	switch (priv->key) {
+	case NFT_CT_STATE:
+		if (ct)
+			state = NF_CT_STATE_BIT(ctinfo);
+		else if (ctinfo == IP_CT_UNTRACKED)
+			state = NF_CT_STATE_UNTRACKED_BIT;
+		else
+			state = NF_CT_STATE_INVALID_BIT;
+		*dest = state;
+		return;
+	case NFT_CT_DIRECTION:
+		nft_reg_store8(dest, CTINFO2DIR(ctinfo));
+		return;
+	case NFT_CT_STATUS:
+		*dest = ct->status;
+		return;
+#ifdef CONFIG_NF_CONNTRACK_MARK
+	case NFT_CT_MARK:
+		*dest = ct->mark;
+		return;
+#endif
+#ifdef CONFIG_NF_CONNTRACK_SECMARK
+	case NFT_CT_SECMARK:
+		*dest = ct->secmark;
+		return;
+#endif
+	default:
+		WARN_ON_ONCE(1);
+		regs->verdict.code = NFT_BREAK;
+		break;
+	}
+}
+EXPORT_SYMBOL_GPL(nft_ct_get_fast_eval);
+#endif