nfp: bpf: record jump destination to simplify jump fixup

eBPF insns are internally organized as dual-list inside NFP offload JIT.
Random access to an insn needs to be done by either forward or backward
traversal along the list.

One place we need to do such traversal is at nfp_fixup_branches where one
traversal is needed for each jump insn to find the destination. Such
traversals could be avoided if jump destinations are collected through a
single travesal in a pre-scan pass, and such information could also be
useful in other places where jump destination info are needed.

This patch adds such jump destination collection in nfp_prog_prepare.

Suggested-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 9 insertions, 48 deletions

diff --git a/drivers/net/ethernet/netronome/nfp/bpf/jit.c b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
index 20daf6b95601..f76659ecb654 100644
--- a/drivers/net/ethernet/netronome/nfp/bpf/jit.c
+++ b/drivers/net/ethernet/netronome/nfp/bpf/jit.c
@@ -66,12 +66,6 @@
 	     next2 = nfp_meta_next(next))
 
 static bool
-nfp_meta_has_next(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
-{
-	return meta->l.next != &nfp_prog->insns;
-}
-
-static bool
 nfp_meta_has_prev(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 {
 	return meta->l.prev != &nfp_prog->insns;
@@ -1864,9 +1858,8 @@ static void br_set_offset(u64 *instr, u16 offset)
 /* --- Assembler logic --- */
 static int nfp_fixup_branches(struct nfp_prog *nfp_prog)
 {
-	struct nfp_insn_meta *meta, *next;
+	struct nfp_insn_meta *meta, *jmp_dst;
 	u32 idx, br_idx;
-	int off;
 
 	list_for_each_entry(meta, &nfp_prog->insns, l) {
 		if (meta->skip)
@@ -1874,13 +1867,10 @@ static int nfp_fixup_branches(struct nfp_prog *nfp_prog)
 		if (BPF_CLASS(meta->insn.code) != BPF_JMP)
 			continue;
 
-		if (list_is_last(&meta->l, &nfp_prog->insns)) {
-			next = NULL;
+		if (list_is_last(&meta->l, &nfp_prog->insns))
 			idx = nfp_prog->last_bpf_off;
-		} else {
-			next = list_next_entry(meta, l);
-			idx = next->off - 1;
-		}
+		else
+			idx = list_next_entry(meta, l)->off - 1;
 
 		br_idx = nfp_prog_offset_to_index(nfp_prog, idx);
 
@@ -1893,43 +1883,14 @@ static int nfp_fixup_branches(struct nfp_prog *nfp_prog)
 		if (FIELD_GET(OP_BR_SPECIAL, nfp_prog->prog[br_idx]))
 			continue;
 
-		/* Find the target offset in assembler realm */
-		off = meta->insn.off;
-		if (!off) {
-			pr_err("Fixup found zero offset!!\n");
+		if (!meta->jmp_dst) {
+			pr_err("Non-exit jump doesn't have destination info recorded!!\n");
 			return -ELOOP;
 		}
 
-		if (!next) {
-			/* When "next" is NULL, "meta" is the last node in the
-			 * list. Given it is an JMP, it then must be a backward
-			 * jump.
-			 *
-			 * For eBPF, the jump offset is against pc + 1, so we
-			 * need to compensate the offset by 1 as we are pointing
-			 * "next" to the current node "meta".
-			 */
-			if (WARN_ON_ONCE(off > -2))
-				return -ELOOP;
-
-			next = meta;
-			off += 1;
-		}
-
-		while (off > 0 && nfp_meta_has_next(nfp_prog, next)) {
-			next = nfp_meta_next(next);
-			off--;
-		}
-		while (off < 0 && nfp_meta_has_prev(nfp_prog, next)) {
-			next = nfp_meta_prev(next);
-			off++;
-		}
-		if (off) {
-			pr_err("Fixup found too large jump!! %d\n", off);
-			return -ELOOP;
-		}
+		jmp_dst = meta->jmp_dst;
 
-		if (next->skip) {
+		if (jmp_dst->skip) {
 			pr_err("Branch landing on removed instruction!!\n");
 			return -ELOOP;
 		}
@@ -1938,7 +1899,7 @@ static int nfp_fixup_branches(struct nfp_prog *nfp_prog)
 		     idx <= br_idx; idx++) {
 			if (!nfp_is_br(nfp_prog->prog[idx]))
 				continue;
-			br_set_offset(&nfp_prog->prog[idx], next->off);
+			br_set_offset(&nfp_prog->prog[idx], jmp_dst->off);
 		}
 	}