From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756575AbbCGCxQ (ORCPT ); Fri, 6 Mar 2015 21:53:16 -0500 Received: from mail-pd0-f173.google.com ([209.85.192.173]:37419 "EHLO mail-pd0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754809AbbCGCuV (ORCPT ); Fri, 6 Mar 2015 21:50:21 -0500 From: John Stultz To: lkml Cc: John Stultz , Dave Jones , Linus Torvalds , Thomas Gleixner , Richard Cochran , Prarit Bhargava , Stephen Boyd , Ingo Molnar , Peter Zijlstra Subject: [PATCH 04/12] clocksource: Add max_cycles to clocksource structure Date: Fri, 6 Mar 2015 18:49:55 -0800 Message-Id: <1425696603-16878-5-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1425696603-16878-1-git-send-email-john.stultz@linaro.org> References: <1425696603-16878-1-git-send-email-john.stultz@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In order to facilitate some clocksource validation, add a max_cycles entry to the structure which will hold the maximum cycle value that can safely be multiplied without potentially causing an overflow. Cc: Dave Jones Cc: Linus Torvalds Cc: Thomas Gleixner Cc: Richard Cochran Cc: Prarit Bhargava Cc: Stephen Boyd Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: John Stultz --- include/linux/clocksource.h | 6 ++++-- kernel/time/clocksource.c | 15 ++++++++++++--- kernel/time/sched_clock.c | 2 +- 3 files changed, 17 insertions(+), 6 deletions(-) diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index 9c78d15..63fe52f 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -56,6 +56,7 @@ struct module; * @shift: cycle to nanosecond divisor (power of two) * @max_idle_ns: max idle time permitted by the clocksource (nsecs) * @maxadj: maximum adjustment value to mult (~11%) + * @max_cycles: maximum safe cycle value which won't overflow on mult * @flags: flags describing special properties * @archdata: arch-specific data * @suspend: suspend function for the clocksource, if necessary @@ -76,7 +77,7 @@ struct clocksource { #ifdef CONFIG_ARCH_CLOCKSOURCE_DATA struct arch_clocksource_data archdata; #endif - + u64 max_cycles; const char *name; struct list_head list; int rating; @@ -189,7 +190,8 @@ extern struct clocksource * __init clocksource_default_clock(void); extern void clocksource_mark_unstable(struct clocksource *cs); extern u64 -clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask); +clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, + u64 *max_cycles); extern void clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec); diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 4988411..e6c752b 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -469,11 +469,14 @@ static u32 clocksource_max_adjustment(struct clocksource *cs) * @shift: cycle to nanosecond divisor (power of two) * @maxadj: maximum adjustment value to mult (~11%) * @mask: bitmask for two's complement subtraction of non 64 bit counters + * @max_cyc: maximum cycle value before potential overflow (does not include + * any saftey margin) * * NOTE: This function includes a saftey margin of 50%, so that bad clock values * can be detected. */ -u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask) +u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, + u64 *max_cyc) { u64 max_nsecs, max_cycles; @@ -493,6 +496,10 @@ u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask) max_cycles = min(max_cycles, mask); max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift); + /* return the max_cycles value as well if requested */ + if (max_cyc) + *max_cyc = max_cycles; + /* Return 50% of the actual maximum, so we can detect bad values */ max_nsecs >>= 1; @@ -671,7 +678,8 @@ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq) } cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, - cs->maxadj, cs->mask); + cs->maxadj, cs->mask, + &cs->max_cycles); } EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale); @@ -719,7 +727,8 @@ int clocksource_register(struct clocksource *cs) /* calculate max idle time permitted for this clocksource */ cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, - cs->maxadj, cs->mask); + cs->maxadj, cs->mask, + &cs->max_cycles); mutex_lock(&clocksource_mutex); clocksource_enqueue(cs); diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index c794b84..d43855b 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -126,7 +126,7 @@ void __init sched_clock_register(u64 (*read)(void), int bits, new_mask = CLOCKSOURCE_MASK(bits); /* calculate how many ns until we risk wrapping */ - wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask); + wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL); new_wrap_kt = ns_to_ktime(wrap); /* update epoch for new counter and update epoch_ns from old counter*/ -- 1.9.1