From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753390AbdBIPPR (ORCPT ); Thu, 9 Feb 2017 10:15:17 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:56735 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753350AbdBIPOr (ORCPT ); Thu, 9 Feb 2017 10:14:47 -0500 Message-Id: <20170209151231.491189912@linutronix.de> User-Agent: quilt/0.63-1 Date: Thu, 09 Feb 2017 16:08:42 +0100 From: Thomas Gleixner To: LKML Cc: x86@kernel.org, Peter Zijlstra , Olof Johansson Subject: [patch 2/2] x86/tsc: Make the TSC ADJUST sanitizing work for tsc_reliable References: <20170209150840.583589315@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=x86-tsc--Make-the-TSC-ADJUST-sanitizing-work-for-tsc_reliable.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When the TSC is marked reliable then the synchronization check is skipped, but that also skips the TSC ADJUST sanitizing code. So on a machine with a wreckaged BIOS the TSC deviation between CPUs might go unnoticed. Let the TSC adjust sanitizing code run unconditionally and just skip the expensive synchronization checks when TSC is marked reliable. Signed-off-by: Thomas Gleixner --- arch/x86/kernel/tsc_sync.c | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-) --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -286,13 +286,6 @@ void check_tsc_sync_source(int cpu) if (unsynchronized_tsc()) return; - if (tsc_clocksource_reliable) { - if (cpu == (nr_cpu_ids-1) || system_state != SYSTEM_BOOTING) - pr_info( - "Skipped synchronization checks as TSC is reliable.\n"); - return; - } - /* * Set the maximum number of test runs to * 1 if the CPU does not provide the TSC_ADJUST MSR @@ -380,14 +373,19 @@ void check_tsc_sync_target(void) int cpus = 2; /* Also aborts if there is no TSC. */ - if (unsynchronized_tsc() || tsc_clocksource_reliable) + if (unsynchronized_tsc()) return; /* * Store, verify and sanitize the TSC adjust register. If * successful skip the test. + * + * The test is also skipped when the TSC is marked reliable. This + * is true for SoCs which have no fallback clocksource. On these + * SoCs the TSC is frequency synchronized, but still the TSC ADJUST + * register might have been wreckaged by the BIOS.. */ - if (tsc_store_and_check_tsc_adjust(false)) { + if (tsc_store_and_check_tsc_adjust(false) || tsc_clocksource_reliable) { atomic_inc(&skip_test); return; }