Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751524AbdFHXvM (ORCPT ); Thu, 8 Jun 2017 19:51:12 -0400 Received: from mail-pg0-f51.google.com ([74.125.83.51]:33981 "EHLO mail-pg0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751442AbdFHXvK (ORCPT ); Thu, 8 Jun 2017 19:51:10 -0400 From: John Stultz To: lkml Cc: Will Deacon , Thomas Gleixner , Ingo Molnar , Miroslav Lichvar , Richard Cochran , Prarit Bhargava , Stephen Boyd , Kevin Brodsky , Daniel Mentz , "stable #4 . 8+" , John Stultz Subject: [PATCH 3/3 v3] arm64: vdso: Fix nsec handling for CLOCK_MONOTONIC_RAW Date: Thu, 8 Jun 2017 16:44:22 -0700 Message-Id: <1496965462-20003-4-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1496965462-20003-1-git-send-email-john.stultz@linaro.org> References: <1496965462-20003-1-git-send-email-john.stultz@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3252 Lines: 78 From: Will Deacon 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. Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Miroslav Lichvar Cc: Richard Cochran Cc: Prarit Bhargava Cc: Stephen Boyd Cc: Kevin Brodsky Cc: Will Deacon Cc: Daniel Mentz Cc: stable #4.8+ Reported-by: John Stultz Acked-by: Kevin Brodsky Tested-by: Daniel Mentz Signed-off-by: Will Deacon [jstultz: minor whitespace tweak, tried to improve commit message to make it more clear this fixes a regression] Signed-off-by: John Stultz --- v2: Tweak commit message to address Ingo's feedback --- 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