[RFC][PATCH 6/9] s390/time: Provide sched_clock_noinstr()

Peter Zijlstra
2023-05-08T21:36:56Z

With the intent to provide local_clock_noinstr(), a variant of
local_clock() that's safe to be called from noinstr code (with the
assumption that any such code will already be non-preemptible),
prepare for things by providing a noinstr sched_clock_noinstr()
function.

Specifically, preempt_enable_*() calls out to schedule(), which upsets
noinstr validation efforts.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/s390/include/asm/timex.h | 13 +++++++++----
arch/s390/kernel/time.c | 11 ++++++++++-
2 files changed, 19 insertions(+), 5 deletions(-)

--- a/arch/s390/include/asm/timex.h
+++ b/arch/s390/include/asm/timex.h
@@ -63,7 +63,7 @@ static inline int store_tod_clock_ext_cc
return cc;
}

-static inline void store_tod_clock_ext(union tod_clock *tod)
+static __always_inline void store_tod_clock_ext(union tod_clock *tod)
{
asm volatile("stcke %0" : "=Q" (*tod) : : "cc");
}
@@ -177,7 +177,7 @@ static inline void local_tick_enable(uns

typedef unsigned long cycles_t;

-static inline unsigned long get_tod_clock(void)
+static __always_inline unsigned long get_tod_clock(void)
{
union tod_clock clk;

@@ -204,6 +204,11 @@ void init_cpu_timer(void);

extern union tod_clock tod_clock_base;

+static __always_inline unsigned long __get_tod_clock_monotonic(void)
+{
+ return get_tod_clock() - tod_clock_base.tod;
+}
+
/**
* get_clock_monotonic - returns current time in clock rate units
*
@@ -216,7 +221,7 @@ static inline unsigned long get_tod_cloc
unsigned long tod;

preempt_disable_notrace();
- tod = get_tod_clock() - tod_clock_base.tod;
+ tod = __get_tod_clock_monotonic();
preempt_enable_notrace();
return tod;
}
@@ -240,7 +245,7 @@ static inline unsigned long get_tod_cloc
* -> ns = (th * 125) + ((tl * 125) >> 9);
*
*/
-static inline unsigned long tod_to_ns(unsigned long todval)
+static __always_inline unsigned long tod_to_ns(unsigned long todval)
{
return ((todval >> 9) * 125) + (((todval & 0x1ff) * 125) >> 9);
}
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -102,12 +102,21 @@ void __init time_early_init(void)
((long) qui.old_leap * 4096000000L);
}

+unsigned long long noinstr sched_clock_noinstr(void)
+{
+ return tod_to_ns(__get_tod_clock_monotonic());
+}
+
/*
* Scheduler clock - returns current time in nanosec units.
*/
unsigned long long notrace sched_clock(void)
{
- return tod_to_ns(get_tod_clock_monotonic());
+ unsigned long long ns;
+ preempt_disable_notrace();
+ ns = tod_to_ns(get_tod_clock_monotonic());
+ preempt_enable_notrace();
+ return ns;
}
NOKPROBE_SYMBOL(sched_clock);