[PATCH v3 6/7] arm64: perf: Add cap_user_time_short

[Leo Yan]

From: Peter Zijlstra <pet...@infradead.org>

This completes the ARM64 cap_user_time support.

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Signed-off-by: Leo Yan <leo....@linaro.org>
---
 arch/arm64/kernel/perf_event.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index c016b116ae33..888bcb5d1388 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -1174,6 +1174,7 @@ void arch_perf_update_userpage(struct perf_event *event,
 
        userpg->cap_user_time = 0;
        userpg->cap_user_time_zero = 0;
+       userpg->cap_user_time_short = 0;
 
        do {
                rd = sched_clock_read_begin(&seq);
@@ -1184,13 +1185,13 @@ void arch_perf_update_userpage(struct perf_event *event,
                userpg->time_mult = rd->mult;
                userpg->time_shift = rd->shift;
                userpg->time_zero = rd->epoch_ns;
+               userpg->time_cycles = rd->epoch_cyc;
+               userpg->time_mask = rd->sched_clock_mask;
 
                /*
-                * This isn't strictly correct, the ARM64 counter can be
-                * 'short' and then we get funnies when it wraps. The correct
-                * thing would be to extend the perf ABI with a cycle and mask
-                * value, but because wrapping on ARM64 is very rare in
-                * practise this 'works'.
+                * Subtract the cycle base, such that software that
+                * doesn't know about cap_user_time_short still 'works'
+                * assuming no wraps.
                 */
                ns = mul_u64_u32_shr(rd->epoch_cyc, rd->mult, rd->shift);
                userpg->time_zero -= ns;
@@ -1216,4 +1217,5 @@ void arch_perf_update_userpage(struct perf_event *event,
         */
        userpg->cap_user_time = 1;
        userpg->cap_user_time_zero = 1;
+       userpg->cap_user_time_short = 1;
 }
-- 
2.17.1