From nobody Sat Feb 7 18:15:40 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 E99E316088F; Mon, 25 Mar 2024 06:42:33 +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=1711348955; cv=none; b=i4wDC2Jx0OO3S2jz4JiK1/Dy0evGhNBLVe+qkfDzFk6+IH8S122GKA5BhmDW/gn1t7gT/mmS4F0y7e881n/9Wq82NxcLAUeKV0v7dcCSukD4Mtw126ljOmD98Md5Q1DUTkwDkAdXQ2QDCTiRjuiGHWJ0H5M3lBSwnmz898jkdUo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711348955; c=relaxed/simple; bh=xuu117cG1lowhe30UpLIG5BgAby+hnwaDFUtdrI4YDU=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=DO7efubDDtCmzv8vv0d9QVQsTc1qBFUtSTjP2u673TWfIkf23EFAKLVlAl7eJyhSw1OUMsRPmrCK29THKtE+iVITZHBPQQ2Sjwjy/zbqPJZijuiaxRnCqO0q1SjxNSYHOlLT9CchuZtDukUKnmdSPjt7sUsErz5GdQSC0gOw8GI= 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=fiUweDl0; 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="fiUweDl0" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1711348954; x=1742884954; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=xuu117cG1lowhe30UpLIG5BgAby+hnwaDFUtdrI4YDU=; b=fiUweDl0XiWKu+0t4CCWMTTtgAkXMgZU6DdRsN3cLJsNHyTzagWnBDLF AfS4B3AsskVYSr8T0xZcyPmm9ScQuUkX1tGa4KqHFY/82z2dD3cb4UVWS vg9ctU+f4x651PySsdVzNe0ZKComNZNg1KnmW/KxquUCjK35VMYRjIcuc 3CnDV5C0//jww8kU0V0tz06F05QtJennssMva8F9IGWz+uhqRGYEEdl1T hx9uggZcnSg0ArEydwc+L1J6k9QT7MkgfStcEm9yv7NS9qxeiNuapn0z1 35zjIIJDI7dBFNPIObb5JtVUCPez15sGNLIXe8fCnkxhzlekMKteFp/fG Q==; X-IronPort-AV: E=McAfee;i="6600,9927,11023"; a="6191576" X-IronPort-AV: E=Sophos;i="6.07,152,1708416000"; d="scan'208";a="6191576" 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 23:42:31 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,152,1708416000"; d="scan'208";a="38629707" 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 23:42:25 -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 17/19] timekeeping: Make delta calculation overflow safe Date: Mon, 25 Mar 2024 08:40:21 +0200 Message-Id: <20240325064023.2997-18-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 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 --- 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 d17484082e2c..111dfdbd488f 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 /** --=20 2.34.1