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

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
---
 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);