nfp: bpf: optimize the adjust_head calls in trivial cases

If the program is simple and has only one adjust head call
with constant parameters, we can check that the call will
always succeed at translation time.  We need to track the
location of the call and make sure parameters are always
the same.  We also have to check the parameters against
datapath constraints and ETH_HLEN.
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

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

@@ -1217,6 +1217,28 @@ static int adjust_head(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 
 	adjust_head = &nfp_prog->bpf->adjust_head;
 
+	/* Optimized version - 5 vs 14 cycles */
+	if (nfp_prog->adjust_head_location != UINT_MAX) {
+		if (WARN_ON_ONCE(nfp_prog->adjust_head_location != meta->n))
+			return -EINVAL;
+
+		emit_alu(nfp_prog, pptr_reg(nfp_prog),
+			 reg_a(2 * 2), ALU_OP_ADD, pptr_reg(nfp_prog));
+		emit_alu(nfp_prog, plen_reg(nfp_prog),
+			 plen_reg(nfp_prog), ALU_OP_SUB, reg_a(2 * 2));
+		emit_alu(nfp_prog, pv_len(nfp_prog),
+			 pv_len(nfp_prog), ALU_OP_SUB, reg_a(2 * 2));
+
+		wrp_immed(nfp_prog, reg_both(0), 0);
+		wrp_immed(nfp_prog, reg_both(1), 0);
+
+		/* TODO: when adjust head is guaranteed to succeed we can
+		 * also eliminate the following if (r0 == 0) branch.
+		 */
+
+		return 0;
+	}
+
 	ret_einval = nfp_prog_current_offset(nfp_prog) + 14;
 	end = ret_einval + 2;
 

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

@@ -172,6 +172,8 @@ nfp_bpf_parse_cap_adjust_head(struct nfp_app_bpf *bpf, void __iomem *value,
 	bpf->adjust_head.flags = readl(&cap->flags);
 	bpf->adjust_head.off_min = readl(&cap->off_min);
 	bpf->adjust_head.off_max = readl(&cap->off_max);
+	bpf->adjust_head.guaranteed_sub = readl(&cap->guaranteed_sub);
+	bpf->adjust_head.guaranteed_add = readl(&cap->guaranteed_add);
 
 	if (bpf->adjust_head.off_min > bpf->adjust_head.off_max) {
 		nfp_err(cpp, "invalid adjust_head TLV: min > max\n");

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

@@ -86,6 +86,8 @@ enum pkt_vec {
  * @flags:		extra flags for adjust head
  * @off_min:		minimal packet offset within buffer required
  * @off_max:		maximum packet offset within buffer required
+ * @guaranteed_sub:	amount of negative adjustment guaranteed possible
+ * @guaranteed_add:	amount of positive adjustment guaranteed possible
  */
 struct nfp_app_bpf {
 	struct nfp_app *app;
@@ -94,6 +96,8 @@ struct nfp_app_bpf {
 		u32 flags;
 		int off_min;
 		int off_max;
+		int guaranteed_sub;
+		int guaranteed_add;
 	} adjust_head;
 };
 
@@ -116,6 +120,7 @@ typedef int (*instr_cb_t)(struct nfp_prog *, struct nfp_insn_meta *);
  * @ptr: pointer type for memory operations
  * @ldst_gather_len: memcpy length gathered from load/store sequence
  * @paired_st: the paired store insn at the head of the sequence
+ * @arg2: arg2 for call instructions
  * @ptr_not_const: pointer is not always constant
  * @jmp_dst: destination info for jump instructions
  * @off: index of first generated machine instruction (in nfp_prog.prog)
@@ -135,6 +140,7 @@ struct nfp_insn_meta {
 			bool ptr_not_const;
 		};
 		struct nfp_insn_meta *jmp_dst;
+		struct bpf_reg_state arg2;
 	};
 	unsigned int off;
 	unsigned short n;
@@ -193,6 +199,7 @@ static inline bool is_mbpf_store(const struct nfp_insn_meta *meta)
  * @n_translated: number of successfully translated instructions (for errors)
  * @error: error code if something went wrong
  * @stack_depth: max stack depth from the verifier
+ * @adjust_head_location: if program has single adjust head call - the insn no.
  * @insns: list of BPF instruction wrappers (struct nfp_insn_meta)
  */
 struct nfp_prog {
@@ -216,6 +223,7 @@ struct nfp_prog {
 	int error;
 
 	unsigned int stack_depth;
+	unsigned int adjust_head_location;
 
 	struct list_head insns;
 };

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

@@ -69,9 +69,47 @@ nfp_bpf_goto_meta(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
 	return meta;
 }
 
+static void
+nfp_record_adjust_head(struct nfp_app_bpf *bpf, struct nfp_prog *nfp_prog,
+		       struct nfp_insn_meta *meta,
+		       const struct bpf_reg_state *reg2)
+{
+	unsigned int location =	UINT_MAX;
+	int imm;
+
+	/* Datapath usually can give us guarantees on how much adjust head
+	 * can be done without the need for any checks.  Optimize the simple
+	 * case where there is only one adjust head by a constant.
+	 */
+	if (reg2->type != SCALAR_VALUE || !tnum_is_const(reg2->var_off))
+		goto exit_set_location;
+	imm = reg2->var_off.value;
+	/* Translator will skip all checks, we need to guarantee min pkt len */
+	if (imm > ETH_ZLEN - ETH_HLEN)
+		goto exit_set_location;
+	if (imm > (int)bpf->adjust_head.guaranteed_add ||
+	    imm < -bpf->adjust_head.guaranteed_sub)
+		goto exit_set_location;
+
+	if (nfp_prog->adjust_head_location) {
+		/* Only one call per program allowed */
+		if (nfp_prog->adjust_head_location != meta->n)
+			goto exit_set_location;
+
+		if (meta->arg2.var_off.value != imm)
+			goto exit_set_location;
+	}
+
+	location = meta->n;
+exit_set_location:
+	nfp_prog->adjust_head_location = location;
+}
+
 static int
-nfp_bpf_check_call(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
+nfp_bpf_check_call(struct nfp_prog *nfp_prog, struct bpf_verifier_env *env,
+		   struct nfp_insn_meta *meta)
 {
+	const struct bpf_reg_state *reg2 = cur_regs(env) + BPF_REG_2;
 	struct nfp_app_bpf *bpf = nfp_prog->bpf;
 	u32 func_id = meta->insn.imm;
 
@@ -85,12 +123,16 @@ nfp_bpf_check_call(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta)
 			pr_warn("adjust_head: FW requires shifting metadata, not supported by the driver\n");
 			return -EOPNOTSUPP;
 		}
+
+		nfp_record_adjust_head(bpf, nfp_prog, meta, reg2);
 		break;
 	default:
 		pr_warn("unsupported function id: %d\n", func_id);
 		return -EOPNOTSUPP;
 	}
 
+	meta->arg2 = *reg2;
+
 	return 0;
 }
 
@@ -204,7 +246,7 @@ nfp_verify_insn(struct bpf_verifier_env *env, int insn_idx, int prev_insn_idx)
 	}
 
 	if (meta->insn.code == (BPF_JMP | BPF_CALL))
-		return nfp_bpf_check_call(nfp_prog, meta);
+		return nfp_bpf_check_call(nfp_prog, env, meta);
 	if (meta->insn.code == (BPF_JMP | BPF_EXIT))
 		return nfp_bpf_check_exit(nfp_prog, env);