Commit c8996c98 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by Alexei Starovoitov
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bpf: Add BPF-helper for accessing CLOCK_TAI 



Commit 3dc6ffae ("timekeeping: Introduce fast accessor to clock tai")
introduced a fast and NMI-safe accessor for CLOCK_TAI. Especially in time
sensitive networks (TSN), where all nodes are synchronized by Precision Time
Protocol (PTP), it's helpful to have the possibility to generate timestamps
based on CLOCK_TAI instead of CLOCK_MONOTONIC. With a BPF helper for TAI in
place, it becomes very convenient to correlate activity across different
machines in the network.

Use cases for such a BPF helper include functionalities such as Tx launch
time (e.g. ETF and TAPRIO Qdiscs) and timestamping.

Note: CLOCK_TAI is nothing new per se, only the NMI-safe variant of it is.

Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
[Kurt: Wrote changelog and renamed helper]
Signed-off-by: default avatarKurt Kanzenbach <kurt@linutronix.de>
Link: https://lore.kernel.org/r/20220809060803.5773-2-kurt@linutronix.de


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent b2d8ef19

include/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -2349,6 +2349,7 @@ extern const struct bpf_func_proto bpf_get_numa_node_id_proto; 
extern const struct bpf_func_proto bpf_tail_call_proto;

extern const struct bpf_func_proto bpf_ktime_get_ns_proto;

extern const struct bpf_func_proto bpf_ktime_get_boot_ns_proto;

extern const struct bpf_func_proto bpf_ktime_get_tai_ns_proto;

extern const struct bpf_func_proto bpf_get_current_pid_tgid_proto;

extern const struct bpf_func_proto bpf_get_current_uid_gid_proto;

extern const struct bpf_func_proto bpf_get_current_comm_proto;

include/uapi/linux/bpf.h

+13 −0
Original line number Diff line number Diff line
@@ -5341,6 +5341,18 @@ union bpf_attr { 
 *		**-EACCES** if the SYN cookie is not valid.

 *

 *		**-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.

 *

 * u64 bpf_ktime_get_tai_ns(void)

 *	Description

 *		A nonsettable system-wide clock derived from wall-clock time but

 *		ignoring leap seconds.  This clock does not experience

 *		discontinuities and backwards jumps caused by NTP inserting leap

 *		seconds as CLOCK_REALTIME does.

 *

 *		See: **clock_gettime**\ (**CLOCK_TAI**)

 *	Return

 *		Current *ktime*.

 *

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -5551,6 +5563,7 @@ union bpf_attr { 
	FN(tcp_raw_gen_syncookie_ipv6),	\

	FN(tcp_raw_check_syncookie_ipv4),	\

	FN(tcp_raw_check_syncookie_ipv6),	\

	FN(ktime_get_tai_ns),		\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper

kernel/bpf/core.c

+1 −0
Original line number Diff line number Diff line
@@ -2623,6 +2623,7 @@ const struct bpf_func_proto bpf_get_numa_node_id_proto __weak; 
const struct bpf_func_proto bpf_ktime_get_ns_proto __weak;

const struct bpf_func_proto bpf_ktime_get_boot_ns_proto __weak;

const struct bpf_func_proto bpf_ktime_get_coarse_ns_proto __weak;

const struct bpf_func_proto bpf_ktime_get_tai_ns_proto __weak;



const struct bpf_func_proto bpf_get_current_pid_tgid_proto __weak;

const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;

kernel/bpf/helpers.c

+14 −0
Original line number Diff line number Diff line
@@ -198,6 +198,18 @@ const struct bpf_func_proto bpf_ktime_get_coarse_ns_proto = { 
	.ret_type	= RET_INTEGER,

};



BPF_CALL_0(bpf_ktime_get_tai_ns)

{

	/* NMI safe access to clock tai */

	return ktime_get_tai_fast_ns();

}



const struct bpf_func_proto bpf_ktime_get_tai_ns_proto = {

	.func		= bpf_ktime_get_tai_ns,

	.gpl_only	= false,

	.ret_type	= RET_INTEGER,

};



BPF_CALL_0(bpf_get_current_pid_tgid)

{

	struct task_struct *task = current;
@@ -1617,6 +1629,8 @@ bpf_base_func_proto(enum bpf_func_id func_id) 
		return &bpf_ktime_get_ns_proto;

	case BPF_FUNC_ktime_get_boot_ns:

		return &bpf_ktime_get_boot_ns_proto;

	case BPF_FUNC_ktime_get_tai_ns:

		return &bpf_ktime_get_tai_ns_proto;

	case BPF_FUNC_ringbuf_output:

		return &bpf_ringbuf_output_proto;

	case BPF_FUNC_ringbuf_reserve:

tools/include/uapi/linux/bpf.h

+13 −0
Original line number Diff line number Diff line
@@ -5341,6 +5341,18 @@ union bpf_attr { 
 *		**-EACCES** if the SYN cookie is not valid.

 *

 *		**-EPROTONOSUPPORT** if CONFIG_IPV6 is not builtin.

 *

 * u64 bpf_ktime_get_tai_ns(void)

 *	Description

 *		A nonsettable system-wide clock derived from wall-clock time but

 *		ignoring leap seconds.  This clock does not experience

 *		discontinuities and backwards jumps caused by NTP inserting leap

 *		seconds as CLOCK_REALTIME does.

 *

 *		See: **clock_gettime**\ (**CLOCK_TAI**)

 *	Return

 *		Current *ktime*.

 *

 */

#define __BPF_FUNC_MAPPER(FN)		\

	FN(unspec),			\
@@ -5551,6 +5563,7 @@ union bpf_attr { 
	FN(tcp_raw_gen_syncookie_ipv6),	\

	FN(tcp_raw_check_syncookie_ipv4),	\

	FN(tcp_raw_check_syncookie_ipv6),	\

	FN(ktime_get_tai_ns),		\

	/* */



/* integer value in 'imm' field of BPF_CALL instruction selects which helper