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bpf: net_sched: Add a qdisc watchdog timer

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Add a watchdog timer to bpf qdisc. The watchdog can be used to schedule
the execution of qdisc through kfunc, bpf_qdisc_schedule(). It can be
useful for building traffic shaping scheduling algorithm, where the time
the next packet will be dequeued is known.

The implementation relies on struct_ops gen_prologue/epilogue to patch bpf
programs provided by users. Operator specific prologue/epilogue kfuncs
are introduced instead of watchdog kfuncs so that it is easier to extend
prologue/epilogue in the future (writing C vs BPF bytecode).

Signed-off-by: Amery Hung <amery.hung@bytedance.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://patch.msgid.link/20250409214606.2000194-5-ameryhung@gmail.com
This commit is contained in:
Amery Hung 2025-04-09 14:46:00 -07:00 committed by Martin KaFai Lau
parent 870c28588a
commit 7a2dafda95
1 changed files with 105 additions and 1 deletions
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106
net/sched/bpf_qdisc.c
View File

@ -13,6 +13,10 @@
static struct bpf_struct_ops bpf_Qdisc_ops;
struct bpf_sched_data {
struct qdisc_watchdog watchdog;
};
struct bpf_sk_buff_ptr {
struct sk_buff *skb;
};
@ -126,6 +130,56 @@ static int bpf_qdisc_btf_struct_access(struct bpf_verifier_log *log,
return 0;
}
BTF_ID_LIST(bpf_qdisc_init_prologue_ids)
BTF_ID(func, bpf_qdisc_init_prologue)
static int bpf_qdisc_gen_prologue(struct bpf_insn *insn_buf, bool direct_write,
const struct bpf_prog *prog)
{
struct bpf_insn *insn = insn_buf;
if (prog->aux->attach_st_ops_member_off != offsetof(struct Qdisc_ops, init))
return 0;
/* r6 = r1; // r6 will be "u64 *ctx". r1 is "u64 *ctx".
* r1 = r1[0]; // r1 will be "struct Qdisc *sch"
* r0 = bpf_qdisc_init_prologue(r1);
* r1 = r6; // r1 will be "u64 *ctx".
*/
*insn++ = BPF_MOV64_REG(BPF_REG_6, BPF_REG_1);
*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_1, 0);
*insn++ = BPF_CALL_KFUNC(0, bpf_qdisc_init_prologue_ids[0]);
*insn++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_6);
*insn++ = prog->insnsi[0];
return insn - insn_buf;
}
BTF_ID_LIST(bpf_qdisc_reset_destroy_epilogue_ids)
BTF_ID(func, bpf_qdisc_reset_destroy_epilogue)
static int bpf_qdisc_gen_epilogue(struct bpf_insn *insn_buf, const struct bpf_prog *prog,
s16 ctx_stack_off)
{
struct bpf_insn *insn = insn_buf;
if (prog->aux->attach_st_ops_member_off != offsetof(struct Qdisc_ops, reset) &&
prog->aux->attach_st_ops_member_off != offsetof(struct Qdisc_ops, destroy))
return 0;
/* r1 = stack[ctx_stack_off]; // r1 will be "u64 *ctx"
* r1 = r1[0]; // r1 will be "struct Qdisc *sch"
* r0 = bpf_qdisc_reset_destroy_epilogue(r1);
* BPF_EXIT;
*/
*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_FP, ctx_stack_off);
*insn++ = BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_1, 0);
*insn++ = BPF_CALL_KFUNC(0, bpf_qdisc_reset_destroy_epilogue_ids[0]);
*insn++ = BPF_EXIT_INSN();
return insn - insn_buf;
}
__bpf_kfunc_start_defs();
/* bpf_skb_get_hash - Get the flow hash of an skb.
@ -154,6 +208,36 @@ __bpf_kfunc void bpf_qdisc_skb_drop(struct sk_buff *skb,
__qdisc_drop(skb, (struct sk_buff **)to_free_list);
}
/* bpf_qdisc_watchdog_schedule - Schedule a qdisc to a later time using a timer.
* @sch: The qdisc to be scheduled.
* @expire: The expiry time of the timer.
* @delta_ns: The slack range of the timer.
*/
__bpf_kfunc void bpf_qdisc_watchdog_schedule(struct Qdisc *sch, u64 expire, u64 delta_ns)
{
struct bpf_sched_data *q = qdisc_priv(sch);
qdisc_watchdog_schedule_range_ns(&q->watchdog, expire, delta_ns);
}
/* bpf_qdisc_init_prologue - Hidden kfunc called in prologue of .init. */
__bpf_kfunc void bpf_qdisc_init_prologue(struct Qdisc *sch)
{
struct bpf_sched_data *q = qdisc_priv(sch);
qdisc_watchdog_init(&q->watchdog, sch);
}
/* bpf_qdisc_reset_destroy_epilogue - Hidden kfunc called in epilogue of .reset
* and .destroy
*/
__bpf_kfunc void bpf_qdisc_reset_destroy_epilogue(struct Qdisc *sch)
{
struct bpf_sched_data *q = qdisc_priv(sch);
qdisc_watchdog_cancel(&q->watchdog);
}
__bpf_kfunc_end_defs();
BTF_KFUNCS_START(qdisc_kfunc_ids)
@ -161,6 +245,9 @@ BTF_ID_FLAGS(func, bpf_skb_get_hash, KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_kfree_skb, KF_RELEASE)
BTF_ID_FLAGS(func, bpf_qdisc_skb_drop, KF_RELEASE)
BTF_ID_FLAGS(func, bpf_dynptr_from_skb, KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_qdisc_watchdog_schedule, KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_qdisc_init_prologue, KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_qdisc_reset_destroy_epilogue, KF_TRUSTED_ARGS)
BTF_KFUNCS_END(qdisc_kfunc_ids)
BTF_SET_START(qdisc_common_kfunc_set)
@ -171,16 +258,22 @@ BTF_SET_END(qdisc_common_kfunc_set)
BTF_SET_START(qdisc_enqueue_kfunc_set)
BTF_ID(func, bpf_qdisc_skb_drop)
BTF_ID(func, bpf_qdisc_watchdog_schedule)
BTF_SET_END(qdisc_enqueue_kfunc_set)
BTF_SET_START(qdisc_dequeue_kfunc_set)
BTF_ID(func, bpf_qdisc_watchdog_schedule)
BTF_SET_END(qdisc_dequeue_kfunc_set)
enum qdisc_ops_kf_flags {
QDISC_OPS_KF_COMMON = 0,
QDISC_OPS_KF_ENQUEUE = 1 << 0,
QDISC_OPS_KF_DEQUEUE = 1 << 1,
};
static const u32 qdisc_ops_context_flags[] = {
[QDISC_OP_IDX(enqueue)] = QDISC_OPS_KF_ENQUEUE,
[QDISC_OP_IDX(dequeue)] = QDISC_OPS_KF_COMMON,
[QDISC_OP_IDX(dequeue)] = QDISC_OPS_KF_DEQUEUE,
[QDISC_OP_IDX(init)] = QDISC_OPS_KF_COMMON,
[QDISC_OP_IDX(reset)] = QDISC_OPS_KF_COMMON,
[QDISC_OP_IDX(destroy)] = QDISC_OPS_KF_COMMON,
@ -203,6 +296,10 @@ static int bpf_qdisc_kfunc_filter(const struct bpf_prog *prog, u32 kfunc_id)
btf_id_set_contains(&qdisc_enqueue_kfunc_set, kfunc_id))
return 0;
if ((flags & QDISC_OPS_KF_DEQUEUE) &&
btf_id_set_contains(&qdisc_dequeue_kfunc_set, kfunc_id))
return 0;
if (btf_id_set_contains(&qdisc_common_kfunc_set, kfunc_id))
return 0;
@ -219,6 +316,8 @@ static const struct bpf_verifier_ops bpf_qdisc_verifier_ops = {
.get_func_proto = bpf_base_func_proto,
.is_valid_access = bpf_qdisc_is_valid_access,
.btf_struct_access = bpf_qdisc_btf_struct_access,
.gen_prologue = bpf_qdisc_gen_prologue,
.gen_epilogue = bpf_qdisc_gen_epilogue,
};
static int bpf_qdisc_init_member(const struct btf_type *t,
@ -234,6 +333,11 @@ static int bpf_qdisc_init_member(const struct btf_type *t,
moff = __btf_member_bit_offset(t, member) / 8;
switch (moff) {
case offsetof(struct Qdisc_ops, priv_size):
if (uqdisc_ops->priv_size)
return -EINVAL;
qdisc_ops->priv_size = sizeof(struct bpf_sched_data);
return 1;
case offsetof(struct Qdisc_ops, peek):
qdisc_ops->peek = qdisc_peek_dequeued;
return 0;