From nobody Sat Feb 7 15:12:34 2026 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 022AA16132B; Mon, 25 Mar 2024 06:42:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.17 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711348966; cv=none; b=gK2JwSk6GyYwVJ9S4Pb92Mox71mS1NyhR9m0kblJ4eDLhIYm6kVYDJWtJdhve7qcvUaqtyuu7ofEXgPVWEuiXXYPbSmJ6mg0q9pSiosuznYe8UPQZo8ij+MPAY4iGsnYtJ3cLScmn9tWEYfbwTEPvpzQUMwMF8XtYmelO7waH58= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711348966; c=relaxed/simple; bh=jWLLlF4KdyRZzGfn4U2lSdQ4Wei7Cj+yXLsz+I6EvZY=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=LE9FZcWd3irT9IPTb6zwdxVOrwrBSrf9nEwHBckP7kQimDWD9bVhpT5Ph+vvMDUeZsbOxOSoKU00Bu7Ds0FKlKWK1mhu10nZ16Z1gNfkOaqTreVELOE+ScKRSIrQSOAGwP6ru/hjFEuEqcHY63BV7mHkNBl2EujTjzooME7ZAbg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=Iusz8THA; arc=none smtp.client-ip=192.198.163.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="Iusz8THA" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1711348965; x=1742884965; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=jWLLlF4KdyRZzGfn4U2lSdQ4Wei7Cj+yXLsz+I6EvZY=; b=Iusz8THA13pqubRw6kvkL5p5vNxVzykvnS/33uQZKIHDT+sb1IA3LO5W OqgjDeLnZvl/26QtHvzEliO4MDb+09t6wQm8fEFboF5kAPLoJT0mNBkPA Y3drThHz2EovOYR9Dx4xU9d1XlODfXO44aVF+ya3xqPSrh/Pv+3FyjmPN PykU0G74QD/wy7uaamV/+vSpJP1sRHWVPke0Oz6Lv7ckGvAzsf3E44uED jd1pJwNHD+9Ih+5c2RkTvIiTFcLY+tPyO2ilQCRUHNbzbhc+hFiV5JMcc Tpr3x3Jng+qxMTIpEaFugbo5lml35Xbt2Z1bH66mkH40gzU/xps9bBVT8 w==; X-IronPort-AV: E=McAfee;i="6600,9927,11023"; a="6191609" X-IronPort-AV: E=Sophos;i="6.07,152,1708416000"; d="scan'208";a="6191609" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Mar 2024 23:42:44 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,152,1708416000"; d="scan'208";a="38629719" Received: from ahunter6-mobl1.ger.corp.intel.com (HELO ahunter-VirtualBox.home\044ger.corp.intel.com) ([10.251.211.155]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Mar 2024 23:42:38 -0700 From: Adrian Hunter To: Thomas Gleixner Cc: Michael Ellerman , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andy Lutomirski , Vincenzo Frascino , John Stultz , Stephen Boyd , Peter Zijlstra , Randy Dunlap , Bjorn Helgaas , Arnd Bergmann , Anna-Maria Behnsen , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Subject: [PATCH V2 19/19] clocksource: Make watchdog and suspend-timing multiplication overflow safe Date: Mon, 25 Mar 2024 08:40:23 +0200 Message-Id: <20240325064023.2997-20-adrian.hunter@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240325064023.2997-1-adrian.hunter@intel.com> References: <20240325064023.2997-1-adrian.hunter@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Kernel timekeeping is designed to keep the change in cycles (since the last timer interrupt) below max_cycles, which prevents multiplication overflow when converting cycles to nanoseconds. However, if timer interrupts stop, the clocksource_cyc2ns() calculation will eventually overflow. Add protection against that. Simplify by folding together clocksource_delta() and clocksource_cyc2ns() into cycles_to_nsec_safe(). Check against max_cycles, falling back to a slower higher precision calculation. Suggested-by: Thomas Gleixner Signed-off-by: Adrian Hunter --- kernel/time/clocksource.c | 42 +++++++++++++++++++-------------------- 1 file changed, 20 insertions(+), 22 deletions(-) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index e5b260aa0e02..4d50d53ac719 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -20,6 +20,16 @@ #include "tick-internal.h" #include "timekeeping_internal.h" =20 +static noinline u64 cycles_to_nsec_safe(struct clocksource *cs, u64 start,= u64 end) +{ + u64 delta =3D clocksource_delta(end, start, cs->mask); + + if (likely(delta < cs->max_cycles)) + return clocksource_cyc2ns(delta, cs->mult, cs->shift); + + return mul_u64_u32_shr(delta, cs->mult, cs->shift); +} + /** * clocks_calc_mult_shift - calculate mult/shift factors for scaled math o= f clocks * @mult: pointer to mult variable @@ -222,8 +232,8 @@ enum wd_read_status { static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *c= snow, u64 *wdnow) { unsigned int nretries, max_retries; - u64 wd_end, wd_end2, wd_delta; int64_t wd_delay, wd_seq_delay; + u64 wd_end, wd_end2; =20 max_retries =3D clocksource_get_max_watchdog_retry(); for (nretries =3D 0; nretries <=3D max_retries; nretries++) { @@ -234,9 +244,7 @@ static enum wd_read_status cs_watchdog_read(struct cloc= ksource *cs, u64 *csnow, wd_end2 =3D watchdog->read(watchdog); local_irq_enable(); =20 - wd_delta =3D clocksource_delta(wd_end, *wdnow, watchdog->mask); - wd_delay =3D clocksource_cyc2ns(wd_delta, watchdog->mult, - watchdog->shift); + wd_delay =3D cycles_to_nsec_safe(watchdog, *wdnow, wd_end); if (wd_delay <=3D WATCHDOG_MAX_SKEW) { if (nretries > 1 || nretries >=3D max_retries) { pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before suc= cess\n", @@ -254,8 +262,7 @@ static enum wd_read_status cs_watchdog_read(struct cloc= ksource *cs, u64 *csnow, * report system busy, reinit the watchdog and skip the current * watchdog test. */ - wd_delta =3D clocksource_delta(wd_end2, wd_end, watchdog->mask); - wd_seq_delay =3D clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->= shift); + wd_seq_delay =3D cycles_to_nsec_safe(watchdog, wd_end, wd_end2); if (wd_seq_delay > WATCHDOG_MAX_SKEW/2) goto skip_test; } @@ -366,8 +373,7 @@ void clocksource_verify_percpu(struct clocksource *cs) delta =3D (csnow_end - csnow_mid) & cs->mask; if (delta < 0) cpumask_set_cpu(cpu, &cpus_ahead); - delta =3D clocksource_delta(csnow_end, csnow_begin, cs->mask); - cs_nsec =3D clocksource_cyc2ns(delta, cs->mult, cs->shift); + cs_nsec =3D cycles_to_nsec_safe(cs, csnow_begin, csnow_end); if (cs_nsec > cs_nsec_max) cs_nsec_max =3D cs_nsec; if (cs_nsec < cs_nsec_min) @@ -398,8 +404,8 @@ static inline void clocksource_reset_watchdog(void) =20 static void clocksource_watchdog(struct timer_list *unused) { - u64 csnow, wdnow, cslast, wdlast, delta; int64_t wd_nsec, cs_nsec, interval; + u64 csnow, wdnow, cslast, wdlast; int next_cpu, reset_pending; struct clocksource *cs; enum wd_read_status read_ret; @@ -456,12 +462,8 @@ static void clocksource_watchdog(struct timer_list *un= used) continue; } =20 - delta =3D clocksource_delta(wdnow, cs->wd_last, watchdog->mask); - wd_nsec =3D clocksource_cyc2ns(delta, watchdog->mult, - watchdog->shift); - - delta =3D clocksource_delta(csnow, cs->cs_last, cs->mask); - cs_nsec =3D clocksource_cyc2ns(delta, cs->mult, cs->shift); + wd_nsec =3D cycles_to_nsec_safe(watchdog, cs->wd_last, wdnow); + cs_nsec =3D cycles_to_nsec_safe(cs, cs->cs_last, csnow); wdlast =3D cs->wd_last; /* save these in case we print them */ cslast =3D cs->cs_last; cs->cs_last =3D csnow; @@ -832,7 +834,7 @@ void clocksource_start_suspend_timing(struct clocksourc= e *cs, u64 start_cycles) */ u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now) { - u64 now, delta, nsec =3D 0; + u64 now, nsec =3D 0; =20 if (!suspend_clocksource) return 0; @@ -847,12 +849,8 @@ u64 clocksource_stop_suspend_timing(struct clocksource= *cs, u64 cycle_now) else now =3D suspend_clocksource->read(suspend_clocksource); =20 - if (now > suspend_start) { - delta =3D clocksource_delta(now, suspend_start, - suspend_clocksource->mask); - nsec =3D mul_u64_u32_shr(delta, suspend_clocksource->mult, - suspend_clocksource->shift); - } + if (now > suspend_start) + nsec =3D cycles_to_nsec_safe(suspend_clocksource, suspend_start, now); =20 /* * Disable the suspend timer to save power if current clocksource is --=20 2.34.1