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arm64/vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW

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Recently vDSO 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.

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>
Git-commit: dbb236c1ceb697a559e0694ac4c9e7b9131d0b16
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Change-Id: Ifa530498a6cd364ef258691ddf03cd3bc2a860b5
[vivekuma@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Vivek Kumar <vivekuma@codeaurora.org>
This commit is contained in:
Will Deacon 2017-06-08 16:44:22 -07:00 • committed by Gerrit - the friendly Code Review server
parent d803000f57
commit e30cb51ecc
1 changed files with 0 additions and 1 deletions
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1
arch/arm64/kernel/vdso/gettimeofday.S
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@ -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