From nobody Sat Feb 7 05:49:04 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 EEDF470CDA; Mon, 8 Apr 2024 13:10:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712581836; cv=none; b=ODWjxZ2FUhVjyy72g2iNA9NnFQcx08deZskPLkNqLLpdr+H1grP8IhjtRVP8av9CIWu/nDx2QTvPnk7EE5Nto5KR7laQs5Bdqnq8YyzwuGhZNhGxLjFzC6iZDIqI5lAWGbOeYRXKLwC+mXRNpkCov+9G1K/1yAjQSNWdDGuyPmY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712581836; c=relaxed/simple; bh=LzmhERQWz0JauYfVzZg0eerqc98SEgrPoVm+gvrV/Uk=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=fpSKYywhdMmT75C5Ly9MNUkWBudl+xADujR/nuRh+utpNIoNYO/JQnK4LRtZAoGU7N5RBFwS6589AuRYZoqgIMrztmwTZECSVt6xZ9VWyBph/9Ow80a6cfWQ+YhGb9arAdsaAWuIbtLoHDUYzKSnmgvyL5B6DMO3qlh7UvKOnCw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=uYPqh8a2; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=3V8GlySB; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="uYPqh8a2"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="3V8GlySB" Date: Mon, 08 Apr 2024 13:10:32 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1712581833; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=S/DcHe2oN/vWLAEYglDVT0qLoZqRQK1arLCcijlMBko=; b=uYPqh8a2LS0t7gvlPq6XFUDtcWykkkNyHWjTIdGYyq4lmaR5n0h3BsArBEUv798WLFMU/+ Q3Ao0EMsMecYRqqV/0H7MGHaib2JFkLFAbvN38twsIAPziFQBYIYQQhxeM23D3JzFeie+p +s3ludvJVi8xh8V0Hb/P0L7UCK5pElWu4EPhBmHak95tZojMj2XjnnCZFK+cKglyvl8oq1 f52jsRawZiy/0ImXa2xoOAnGdJ7CU6iB3ZYxIHO8V4s/QaBqAnIjABORuGZYuX6LeyWdEl 6OhHMqL/NzdQkWeUTbwghlpPoeSoU2PiA2FMVJzJN35X+yOn4s4NX0Mtim9CDg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1712581833; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=S/DcHe2oN/vWLAEYglDVT0qLoZqRQK1arLCcijlMBko=; b=3V8GlySBrNWM51iwF2R+ysnI6cVM9QmLGr7qkkgn8b+TH2PwYKzv763apvITrinZi5CSSZ M8yiITRqqruSNKBg== From: "tip-bot2 for Adrian Hunter" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: timers/core] timekeeping: Make delta calculation overflow safe Cc: Thomas Gleixner , Adrian Hunter , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20240325064023.2997-18-adrian.hunter@intel.com> References: <20240325064023.2997-18-adrian.hunter@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <171258183251.10875.11815766189423599401.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the timers/core branch of tip: Commit-ID: fcf190c369149c3b04539797cedf28741eb14164 Gitweb: https://git.kernel.org/tip/fcf190c369149c3b04539797cedf28741= eb14164 Author: Adrian Hunter AuthorDate: Mon, 25 Mar 2024 08:40:21 +02:00 Committer: Thomas Gleixner CommitterDate: Mon, 08 Apr 2024 15:03:08 +02:00 timekeeping: Make delta calculation overflow safe 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 calculation will eventually overflow. Add protection against that. In timekeeping_cycles_to_ns() calculation, check against max_cycles, falling back to a slower higher precision calculation. In timekeeping_forward_now(), process delta in chunks of at most max_cycles. Suggested-by: Thomas Gleixner Signed-off-by: Adrian Hunter Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20240325064023.2997-18-adrian.hunter@intel.= com --- kernel/time/timekeeping.c | 40 +++++++++++++++++++++++++++----------- 1 file changed, 29 insertions(+), 11 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index d174840..111dfdb 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -364,19 +364,32 @@ static void tk_setup_internals(struct timekeeper *tk,= struct clocksource *clock) } =20 /* Timekeeper helper functions. */ +static noinline u64 delta_to_ns_safe(const struct tk_read_base *tkr, u64 d= elta) +{ + return mul_u64_u32_add_u64_shr(delta, tkr->mult, tkr->xtime_nsec, tkr->sh= ift); +} + static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr,= u64 cycles) { /* Calculate the delta since the last update_wall_time() */ u64 mask =3D tkr->mask, delta =3D (cycles - tkr->cycle_last) & mask; =20 - if (IS_ENABLED(CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE)) { - /* - * Handle clocksource inconsistency between CPUs to prevent - * time from going backwards by checking for the MSB of the - * mask being set in the delta. - */ - if (unlikely(delta & ~(mask >> 1))) - return tkr->xtime_nsec >> tkr->shift; + /* + * This detects the case where the delta overflows the multiplication + * with tkr->mult. + */ + if (unlikely(delta > tkr->clock->max_cycles)) { + if (IS_ENABLED(CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE)) { + /* + * Handle clocksource inconsistency between CPUs to prevent + * time from going backwards by checking for the MSB of the + * mask being set in the delta. + */ + if (unlikely(delta & ~(mask >> 1))) + return tkr->xtime_nsec >> tkr->shift; + } + + return delta_to_ns_safe(tkr, delta); } =20 return ((delta * tkr->mult) + tkr->xtime_nsec) >> tkr->shift; @@ -789,10 +802,15 @@ static void timekeeping_forward_now(struct timekeeper= *tk) tk->tkr_mono.cycle_last =3D cycle_now; tk->tkr_raw.cycle_last =3D cycle_now; =20 - tk->tkr_mono.xtime_nsec +=3D delta * tk->tkr_mono.mult; - tk->tkr_raw.xtime_nsec +=3D delta * tk->tkr_raw.mult; + while (delta > 0) { + u64 max =3D tk->tkr_mono.clock->max_cycles; + u64 incr =3D delta < max ? delta : max; =20 - tk_normalize_xtime(tk); + tk->tkr_mono.xtime_nsec +=3D incr * tk->tkr_mono.mult; + tk->tkr_raw.xtime_nsec +=3D incr * tk->tkr_raw.mult; + tk_normalize_xtime(tk); + delta -=3D incr; + } } =20 /**