From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2109CC7112A for ; Sun, 14 Oct 2018 16:04:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DC2D020645 for ; Sun, 14 Oct 2018 16:04:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DC2D020645 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728001AbeJNXpp (ORCPT ); Sun, 14 Oct 2018 19:45:45 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:35682 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727042AbeJNXLn (ORCPT ); Sun, 14 Oct 2018 19:11:43 -0400 Received: from [2a02:8011:400e:2:cbab:f00:c93f:614] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1gBiLV-0004cg-Ha; Sun, 14 Oct 2018 16:30:21 +0100 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1gBiLT-0000MU-4v; Sun, 14 Oct 2018 16:30:19 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Thomas Gleixner" , peterz@infradead.org, hpa@zytor.com, "Xiaoming Gao" , "Xiaoming Gao" Date: Sun, 14 Oct 2018 16:25:41 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 163/366] x86/tsc: Prevent 32bit truncation in calc_hpet_ref() In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:cbab:f00:c93f:614 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.60-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Xiaoming Gao commit d3878e164dcd3925a237a20e879432400e369172 upstream. 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: peterz@infradead.org Cc: hpa@zytor.com Link: https://lkml.kernel.org/r/38894564-4fc9-b8ec-353f-de702839e44e@gmail.com Signed-off-by: Ben Hutchings --- arch/x86/kernel/tsc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -398,7 +398,7 @@ static unsigned long calc_hpet_ref(u64 d 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; }