nfp: bpf: xdp_adjust_tail support

Add support for adjust_tail.  There are no FW changes needed but add
a FW capability just in case there would be any issue with previously
released FW, or we will have to change the ABI in the future.

The helper is trivial and shouldn't be used too often so just inline
the body of the function.  We add the delta to locally maintained
packet length register and check for overflow, since add of negative
value must overflow if result is positive.  Note that if delta of 0
would be allowed in the kernel this trick stops working and we need
one more instruction to compare lengths before and after the change.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

drivers/net/ethernet/netronome/nfp/bpf/fw.h

@@ -51,6 +51,7 @@ enum bpf_cap_tlv_type {
 	NFP_BPF_CAP_TYPE_MAPS		= 3,
 	NFP_BPF_CAP_TYPE_RANDOM		= 4,
 	NFP_BPF_CAP_TYPE_QUEUE_SELECT	= 5,
+	NFP_BPF_CAP_TYPE_ADJUST_TAIL	= 6,
 };
 
 struct nfp_bpf_cap_tlv_func {

drivers/net/ethernet/netronome/nfp/bpf/jit.c

@@ -1642,6 +1642,51 @@ static int adjust_head(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 	return 0;
 }
 
+static int adjust_tail(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
+{
+	u32 ret_einval, end;
+	swreg plen, delta;
+
+	BUILD_BUG_ON(plen_reg(nfp_prog) != reg_b(STATIC_REG_PKT_LEN));
+
+	plen = imm_a(nfp_prog);
+	delta = reg_a(2 * 2);
+
+	ret_einval = nfp_prog_current_offset(nfp_prog) + 9;
+	end = nfp_prog_current_offset(nfp_prog) + 11;
+
+	/* Calculate resulting length */
+	emit_alu(nfp_prog, plen, plen_reg(nfp_prog), ALU_OP_ADD, delta);
+	/* delta == 0 is not allowed by the kernel, add must overflow to make
+	 * length smaller.
+	 */
+	emit_br(nfp_prog, BR_BCC, ret_einval, 0);
+
+	/* if (new_len < 14) then -EINVAL */
+	emit_alu(nfp_prog, reg_none(), plen, ALU_OP_SUB, reg_imm(ETH_HLEN));
+	emit_br(nfp_prog, BR_BMI, ret_einval, 0);
+
+	emit_alu(nfp_prog, plen_reg(nfp_prog),
+		 plen_reg(nfp_prog), ALU_OP_ADD, delta);
+	emit_alu(nfp_prog, pv_len(nfp_prog),
+		 pv_len(nfp_prog), ALU_OP_ADD, delta);
+
+	emit_br(nfp_prog, BR_UNC, end, 2);
+	wrp_immed(nfp_prog, reg_both(0), 0);
+	wrp_immed(nfp_prog, reg_both(1), 0);
+
+	if (!nfp_prog_confirm_current_offset(nfp_prog, ret_einval))
+		return -EINVAL;
+
+	wrp_immed(nfp_prog, reg_both(0), -22);
+	wrp_immed(nfp_prog, reg_both(1), ~0);
+
+	if (!nfp_prog_confirm_current_offset(nfp_prog, end))
+		return -EINVAL;
+
+	return 0;
+}
+
 static int
 map_call_stack_common(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 {
@@ -3041,6 +3086,8 @@ static int call(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 	switch (meta->insn.imm) {
 	case BPF_FUNC_xdp_adjust_head:
 		return adjust_head(nfp_prog, meta);
+	case BPF_FUNC_xdp_adjust_tail:
+		return adjust_tail(nfp_prog, meta);
 	case BPF_FUNC_map_lookup_elem:
 	case BPF_FUNC_map_update_elem:
 	case BPF_FUNC_map_delete_elem:

drivers/net/ethernet/netronome/nfp/bpf/main.c

@@ -334,6 +334,14 @@ nfp_bpf_parse_cap_qsel(struct nfp_app_bpf *bpf, void __iomem *value, u32 length)
 	return 0;
 }
 
+static int
+nfp_bpf_parse_cap_adjust_tail(struct nfp_app_bpf *bpf, void __iomem *value,
+			      u32 length)
+{
+	bpf->adjust_tail = true;
+	return 0;
+}
+
 static int nfp_bpf_parse_capabilities(struct nfp_app *app)
 {
 	struct nfp_cpp *cpp = app->pf->cpp;
@@ -380,6 +388,11 @@ static int nfp_bpf_parse_capabilities(struct nfp_app *app)
 			if (nfp_bpf_parse_cap_qsel(app->priv, value, length))
 				goto err_release_free;
 			break;
+		case NFP_BPF_CAP_TYPE_ADJUST_TAIL:
+			if (nfp_bpf_parse_cap_adjust_tail(app->priv, value,
+							  length))
+				goto err_release_free;
+			break;
 		default:
 			nfp_dbg(cpp, "unknown BPF capability: %d\n", type);
 			break;

drivers/net/ethernet/netronome/nfp/bpf/main.h

@@ -150,6 +150,7 @@ enum pkt_vec {
  *
  * @pseudo_random:	FW initialized the pseudo-random machinery (CSRs)
  * @queue_select:	BPF can set the RX queue ID in packet vector
+ * @adjust_tail:	BPF can simply trunc packet size for adjust tail
  */
 struct nfp_app_bpf {
 	struct nfp_app *app;
@@ -195,6 +196,7 @@ struct nfp_app_bpf {
 
 	bool pseudo_random;
 	bool queue_select;
+	bool adjust_tail;
 };
 
 enum nfp_bpf_map_use {

drivers/net/ethernet/netronome/nfp/bpf/verifier.c

@@ -178,6 +178,13 @@ nfp_bpf_check_call(struct nfp_prog *nfp_prog, struct bpf_verifier_env *env,
 		nfp_record_adjust_head(bpf, nfp_prog, meta, reg2);
 		break;
 
+	case BPF_FUNC_xdp_adjust_tail:
+		if (!bpf->adjust_tail) {
+			pr_vlog(env, "adjust_tail not supported by FW\n");
+			return -EOPNOTSUPP;
+		}
+		break;
+
 	case BPF_FUNC_map_lookup_elem:
 		if (!nfp_bpf_map_call_ok("map_lookup", env, meta,
 					 bpf->helpers.map_lookup, reg1) ||

drivers/net/ethernet/netronome/nfp/nfp_asm.h

@@ -93,6 +93,7 @@ enum br_mask {
 	BR_BNE = 0x01,
 	BR_BMI = 0x02,
 	BR_BHS = 0x04,
+	BR_BCC = 0x05,
 	BR_BLO = 0x05,
 	BR_BGE = 0x08,
 	BR_BLT = 0x09,