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arm64/vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW 

Recently vDSO support for CLOCK_MONOTONIC_RAW was added in
49eea433b3 ("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.

Unfortunately, by accellerating the MONOTONIC_RAW clockid, it
uncovered potential 1ns time inconsistencies caused by the
timekeeping core not handing sub-ns resolution.

Now that the core code has been fixed and 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, in order to
fix the user-visible inconsistency. 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.

[jstultz: minor whitespace tweak, tried to improve commit
 message to make it more clear this fixes a regression]
Reported-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Tested-by: Daniel Mentz <danielmentz@google.com>
Acked-by: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <stephen.boyd@linaro.org>
Cc: "stable #4 . 8+" <stable@vger.kernel.org>
Cc: Miroslav Lichvar <mlichvar@redhat.com>
Link: http://lkml.kernel.org/r/1496965462-20003-4-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Will Deacon 2017-06-08 16:44:22 -07:00 committed by Thomas Gleixner
parent 3d88d56c58
commit dbb236c1ce
2 changed files with 3 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
arch/arm64/kernel/vdso.c
View File

@ -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 */

1
arch/arm64/kernel/vdso/gettimeofday.S
View File

@ -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