Patch "arm64/vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

arm64/vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-vdso-fix-nsec-handling-for-clock_monotonic_raw.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Will Deacon <[email protected]>
Date: Thu, 8 Jun 2017 16:44:22 -0700
Subject: arm64/vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW

From: Will Deacon <[email protected]>

commit dbb236c1ceb697a559e0694ac4c9e7b9131d0b16 upstream.

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]

---
 arch/arm64/kernel/vdso.c              |    5 +++--
 arch/arm64/kernel/vdso/gettimeofday.S |    1 -
 2 files changed, 3 insertions(+), 3 deletions(-)

@@ -217,10 +217,11 @@ void update_vsyscall(struct timekeeper *
 		/* 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 */

@@ -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
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/time-fix-clock_monotonic_raw-sub-nanosecond-accounting.patch queue-4.9/arm64-vdso-fix-nsec-handling-for-clock_monotonic_raw.patch