From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752199AbeDQJ5F (ORCPT ); Tue, 17 Apr 2018 05:57:05 -0400 Received: from terminus.zytor.com ([198.137.202.136]:57719 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751243AbeDQJ5E (ORCPT ); Tue, 17 Apr 2018 05:57:04 -0400 Date: Tue, 17 Apr 2018 02:56:30 -0700 From: tip-bot for Xiaoming Gao Message-ID: Cc: tglx@linutronix.de, hpa@zytor.com, gxm.linux.kernel@gmail.com, linux-kernel@vger.kernel.org, newtongao@tencent.com, mingo@kernel.org Reply-To: gxm.linux.kernel@gmail.com, hpa@zytor.com, tglx@linutronix.de, mingo@kernel.org, newtongao@tencent.com, linux-kernel@vger.kernel.org In-Reply-To: <38894564-4fc9-b8ec-353f-de702839e44e@gmail.com> References: <38894564-4fc9-b8ec-353f-de702839e44e@gmail.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/tsc: Prevent 32bit truncation in calc_hpet_ref() Git-Commit-ID: d3878e164dcd3925a237a20e879432400e369172 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: d3878e164dcd3925a237a20e879432400e369172 Gitweb: https://git.kernel.org/tip/d3878e164dcd3925a237a20e879432400e369172 Author: Xiaoming Gao AuthorDate: Fri, 13 Apr 2018 17:48:08 +0800 Committer: Thomas Gleixner CommitDate: Tue, 17 Apr 2018 11:50:42 +0200 x86/tsc: Prevent 32bit truncation in calc_hpet_ref() The TSC calibration code uses HPET as reference. The conversion normalizes the delta of two HPET timestamps: hpetref = ((tshpet1 - tshpet2) * HPET_PERIOD) / 1e6 and then divides the normalized delta of the corresponding TSC timestamps by the result to calulate the TSC frequency. tscfreq = ((tstsc1 - tstsc2 ) * 1e6) / hpetref This uses do_div() which takes an u32 as the divisor, which worked so far because the HPET frequency was low enough that 'hpetref' never exceeded 32bit. On Skylake machines the HPET frequency increased so 'hpetref' can exceed 32bit. do_div() truncates the divisor, which causes the calibration to fail. Use div64_u64() to avoid the problem. [ tglx: Fixes whitespace mangled patch and rewrote changelog ] Signed-off-by: Xiaoming Gao Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Cc: peterz@infradead.org Cc: hpa@zytor.com Link: https://lkml.kernel.org/r/38894564-4fc9-b8ec-353f-de702839e44e@gmail.com --- arch/x86/kernel/tsc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index ef32297ff17e..91e6da48cbb6 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -317,7 +317,7 @@ static unsigned long calc_hpet_ref(u64 deltatsc, u64 hpet1, u64 hpet2) hpet2 -= hpet1; tmp = ((u64)hpet2 * hpet_readl(HPET_PERIOD)); do_div(tmp, 1000000); - do_div(deltatsc, tmp); + deltatsc = div64_u64(deltatsc, tmp); return (unsigned long) deltatsc; }