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Subject[RFC][PATCH 3/4] arm64: vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW
Date
From: Will Deacon <will.deacon@arm.com>

Commit 45a7905fc48f ("arm64: vdso: defer shifting of nanosecond
component of timespec") fixed sub-ns inaccuracies in our vDSO
clock_gettime implementation by deferring the right-shift of the
nanoseconds components until after the timespec addition, which
operates on left-shifted values. That worked nicely until
support for CLOCK_MONOTONIC_RAW was added in 49eea433b326
("arm64: Add support for CLOCK_MONOTONIC_RAW in clock_gettime()
vDSO"). Noticing that the core timekeeping code never set
tkr_raw.xtime_nsec, the vDSO implementation didn't bother
exposing it via the data page and instead took the unshifted
tk->raw_time.tv_nsec value which was then immediately shifted
left in the vDSO code.

Now that the core code is actually setting tkr_raw.xtime_nsec,
we need to take that into account in the vDSO by adding it to
the shifted raw_time value. Rather than do that at each use (and
expand the data page in the process), instead perform the
shift/addition operation when populating the data page and
remove the shift from the vDSO code entirely.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Stephen Boyd <stephen.boyd@linaro.org>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Daniel Mentz <danielmentz@google.com>
Reported-by: John Stultz <john.stultz@linaro.org>
Acked-by: Acked-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
[jstultz: minor whitespace tweak]
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
arch/arm64/kernel/vdso.c | 5 +++--
arch/arm64/kernel/vdso/gettimeofday.S | 1 -
2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 41b6e31..d0cb007 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -221,10 +221,11 @@ void update_vsyscall(struct timekeeper *tk)
/* tkr_mono.cycle_last == tkr_raw.cycle_last */
vdso_data->cs_cycle_last = tk->tkr_mono.cycle_last;
vdso_data->raw_time_sec = tk->raw_time.tv_sec;
- vdso_data->raw_time_nsec = tk->raw_time.tv_nsec;
+ vdso_data->raw_time_nsec = (tk->raw_time.tv_nsec <<
+ tk->tkr_raw.shift) +
+ tk->tkr_raw.xtime_nsec;
vdso_data->xtime_clock_sec = tk->xtime_sec;
vdso_data->xtime_clock_nsec = tk->tkr_mono.xtime_nsec;
- /* tkr_raw.xtime_nsec == 0 */
vdso_data->cs_mono_mult = tk->tkr_mono.mult;
vdso_data->cs_raw_mult = tk->tkr_raw.mult;
/* tkr_mono.shift == tkr_raw.shift */
diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
index e00b467..76320e9 100644
--- a/arch/arm64/kernel/vdso/gettimeofday.S
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -256,7 +256,6 @@ monotonic_raw:
seqcnt_check fail=monotonic_raw

/* All computations are done with left-shifted nsecs. */
- lsl x14, x14, x12
get_nsec_per_sec res=x9
lsl x9, x9, x12

--
2.7.4
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