1// SPDX-License-Identifier: GPL-2.0
2/* Copyright (c) 2019 Facebook */
3
4/* WARNING: This implemenation is not necessarily the same
5 * as the tcp_dctcp.c.  The purpose is mainly for testing
6 * the kernel BPF logic.
7 */
8
9#include <stddef.h>
10#include <linux/bpf.h>
11#include <linux/types.h>
12#include <linux/stddef.h>
13#include <linux/tcp.h>
14#include <bpf/bpf_helpers.h>
15#include <bpf/bpf_tracing.h>
16#include "bpf_tcp_helpers.h"
17
18char _license[] SEC("license") = "GPL";
19
20int stg_result = 0;
21
22struct {
23	__uint(type, BPF_MAP_TYPE_SK_STORAGE);
24	__uint(map_flags, BPF_F_NO_PREALLOC);
25	__type(key, int);
26	__type(value, int);
27} sk_stg_map SEC(".maps");
28
29#define DCTCP_MAX_ALPHA	1024U
30
31struct dctcp {
32	__u32 old_delivered;
33	__u32 old_delivered_ce;
34	__u32 prior_rcv_nxt;
35	__u32 dctcp_alpha;
36	__u32 next_seq;
37	__u32 ce_state;
38	__u32 loss_cwnd;
39};
40
41static unsigned int dctcp_shift_g = 4; /* g = 1/2^4 */
42static unsigned int dctcp_alpha_on_init = DCTCP_MAX_ALPHA;
43
44static __always_inline void dctcp_reset(const struct tcp_sock *tp,
45					struct dctcp *ca)
46{
47	ca->next_seq = tp->snd_nxt;
48
49	ca->old_delivered = tp->delivered;
50	ca->old_delivered_ce = tp->delivered_ce;
51}
52
53SEC("struct_ops/dctcp_init")
54void BPF_PROG(dctcp_init, struct sock *sk)
55{
56	const struct tcp_sock *tp = tcp_sk(sk);
57	struct dctcp *ca = inet_csk_ca(sk);
58	int *stg;
59
60	ca->prior_rcv_nxt = tp->rcv_nxt;
61	ca->dctcp_alpha = min(dctcp_alpha_on_init, DCTCP_MAX_ALPHA);
62	ca->loss_cwnd = 0;
63	ca->ce_state = 0;
64
65	stg = bpf_sk_storage_get(&sk_stg_map, (void *)tp, NULL, 0);
66	if (stg) {
67		stg_result = *stg;
68		bpf_sk_storage_delete(&sk_stg_map, (void *)tp);
69	}
70	dctcp_reset(tp, ca);
71}
72
73SEC("struct_ops/dctcp_ssthresh")
74__u32 BPF_PROG(dctcp_ssthresh, struct sock *sk)
75{
76	struct dctcp *ca = inet_csk_ca(sk);
77	struct tcp_sock *tp = tcp_sk(sk);
78
79	ca->loss_cwnd = tp->snd_cwnd;
80	return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U);
81}
82
83SEC("struct_ops/dctcp_update_alpha")
84void BPF_PROG(dctcp_update_alpha, struct sock *sk, __u32 flags)
85{
86	const struct tcp_sock *tp = tcp_sk(sk);
87	struct dctcp *ca = inet_csk_ca(sk);
88
89	/* Expired RTT */
90	if (!before(tp->snd_una, ca->next_seq)) {
91		__u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce;
92		__u32 alpha = ca->dctcp_alpha;
93
94		/* alpha = (1 - g) * alpha + g * F */
95
96		alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g);
97		if (delivered_ce) {
98			__u32 delivered = tp->delivered - ca->old_delivered;
99
100			/* If dctcp_shift_g == 1, a 32bit value would overflow
101			 * after 8 M packets.
102			 */
103			delivered_ce <<= (10 - dctcp_shift_g);
104			delivered_ce /= max(1U, delivered);
105
106			alpha = min(alpha + delivered_ce, DCTCP_MAX_ALPHA);
107		}
108		ca->dctcp_alpha = alpha;
109		dctcp_reset(tp, ca);
110	}
111}
112
113static __always_inline void dctcp_react_to_loss(struct sock *sk)
114{
115	struct dctcp *ca = inet_csk_ca(sk);
116	struct tcp_sock *tp = tcp_sk(sk);
117
118	ca->loss_cwnd = tp->snd_cwnd;
119	tp->snd_ssthresh = max(tp->snd_cwnd >> 1U, 2U);
120}
121
122SEC("struct_ops/dctcp_state")
123void BPF_PROG(dctcp_state, struct sock *sk, __u8 new_state)
124{
125	if (new_state == TCP_CA_Recovery &&
126	    new_state != BPF_CORE_READ_BITFIELD(inet_csk(sk), icsk_ca_state))
127		dctcp_react_to_loss(sk);
128	/* We handle RTO in dctcp_cwnd_event to ensure that we perform only
129	 * one loss-adjustment per RTT.
130	 */
131}
132
133static __always_inline void dctcp_ece_ack_cwr(struct sock *sk, __u32 ce_state)
134{
135	struct tcp_sock *tp = tcp_sk(sk);
136
137	if (ce_state == 1)
138		tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
139	else
140		tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
141}
142
143/* Minimal DCTP CE state machine:
144 *
145 * S:	0 <- last pkt was non-CE
146 *	1 <- last pkt was CE
147 */
148static __always_inline
149void dctcp_ece_ack_update(struct sock *sk, enum tcp_ca_event evt,
150			  __u32 *prior_rcv_nxt, __u32 *ce_state)
151{
152	__u32 new_ce_state = (evt == CA_EVENT_ECN_IS_CE) ? 1 : 0;
153
154	if (*ce_state != new_ce_state) {
155		/* CE state has changed, force an immediate ACK to
156		 * reflect the new CE state. If an ACK was delayed,
157		 * send that first to reflect the prior CE state.
158		 */
159		if (inet_csk(sk)->icsk_ack.pending & ICSK_ACK_TIMER) {
160			dctcp_ece_ack_cwr(sk, *ce_state);
161			bpf_tcp_send_ack(sk, *prior_rcv_nxt);
162		}
163		inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
164	}
165	*prior_rcv_nxt = tcp_sk(sk)->rcv_nxt;
166	*ce_state = new_ce_state;
167	dctcp_ece_ack_cwr(sk, new_ce_state);
168}
169
170SEC("struct_ops/dctcp_cwnd_event")
171void BPF_PROG(dctcp_cwnd_event, struct sock *sk, enum tcp_ca_event ev)
172{
173	struct dctcp *ca = inet_csk_ca(sk);
174
175	switch (ev) {
176	case CA_EVENT_ECN_IS_CE:
177	case CA_EVENT_ECN_NO_CE:
178		dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state);
179		break;
180	case CA_EVENT_LOSS:
181		dctcp_react_to_loss(sk);
182		break;
183	default:
184		/* Don't care for the rest. */
185		break;
186	}
187}
188
189SEC("struct_ops/dctcp_cwnd_undo")
190__u32 BPF_PROG(dctcp_cwnd_undo, struct sock *sk)
191{
192	const struct dctcp *ca = inet_csk_ca(sk);
193
194	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
195}
196
197SEC("struct_ops/tcp_reno_cong_avoid")
198void BPF_PROG(tcp_reno_cong_avoid, struct sock *sk, __u32 ack, __u32 acked)
199{
200	struct tcp_sock *tp = tcp_sk(sk);
201
202	if (!tcp_is_cwnd_limited(sk))
203		return;
204
205	/* In "safe" area, increase. */
206	if (tcp_in_slow_start(tp)) {
207		acked = tcp_slow_start(tp, acked);
208		if (!acked)
209			return;
210	}
211	/* In dangerous area, increase slowly. */
212	tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
213}
214
215SEC(".struct_ops")
216struct tcp_congestion_ops dctcp_nouse = {
217	.init		= (void *)dctcp_init,
218	.set_state	= (void *)dctcp_state,
219	.flags		= TCP_CONG_NEEDS_ECN,
220	.name		= "bpf_dctcp_nouse",
221};
222
223SEC(".struct_ops")
224struct tcp_congestion_ops dctcp = {
225	.init		= (void *)dctcp_init,
226	.in_ack_event   = (void *)dctcp_update_alpha,
227	.cwnd_event	= (void *)dctcp_cwnd_event,
228	.ssthresh	= (void *)dctcp_ssthresh,
229	.cong_avoid	= (void *)tcp_reno_cong_avoid,
230	.undo_cwnd	= (void *)dctcp_cwnd_undo,
231	.set_state	= (void *)dctcp_state,
232	.flags		= TCP_CONG_NEEDS_ECN,
233	.name		= "bpf_dctcp",
234};
235