From: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Commit 3dc6ffae2da2 ("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: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
[Kurt: Wrote changelog and renamed helper]
Signed-off-by: Kurt Kanzenbach <kurt@xxxxxxxxxxxxx>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 13 +++++++++++++
kernel/bpf/core.c | 1 +
kernel/bpf/helpers.c | 14 ++++++++++++++
tools/include/uapi/linux/bpf.h | 13 +++++++++++++
5 files changed, 42 insertions(+)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 20c26aed7896..a627a02cf8ab 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -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;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 534e33fb1029..7d1e2794d83e 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -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
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index c1e10d088dbb..639437f36928 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -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;
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 1f961f9982d2..a95eb9fb01ff 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -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:
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index f58d58e1d547..e174ad28aeb7 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -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
--
2.30.2
