From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753525AbcKSNvi (ORCPT ); Sat, 19 Nov 2016 08:51:38 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:53738 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752752AbcKSNuN (ORCPT ); Sat, 19 Nov 2016 08:50:13 -0500 Message-Id: <20161119134017.574838461@linutronix.de> User-Agent: quilt/0.63-1 Date: Sat, 19 Nov 2016 13:47:35 -0000 From: Thomas Gleixner To: LKML Cc: Ingo Molnar , Peter Zijlstra , x86@kernel.org, Borislav Petkov , Yinghai Lu Subject: [patch 2/8] x86/tsc: Detect random warps References: <20161119133816.633700010@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=x86-tsc--Detect-random-warps.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If time warps can be observed then they should only ever be observed on one CPU. If they are observed on both CPUs then the system is completely hosed. Add a check for this condition and notify if it happens. Signed-off-by: Thomas Gleixner --- arch/x86/kernel/tsc_sync.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -37,6 +37,7 @@ static arch_spinlock_t sync_lock = __ARC static cycles_t last_tsc; static cycles_t max_warp; static int nr_warps; +static int random_warps; /* * TSC-warp measurement loop running on both CPUs. This is not called @@ -45,7 +46,7 @@ static int nr_warps; static void check_tsc_warp(unsigned int timeout) { cycles_t start, now, prev, end; - int i; + int i, cur_warps = 0; start = rdtsc_ordered(); /* @@ -85,7 +86,14 @@ static void check_tsc_warp(unsigned int if (unlikely(prev > now)) { arch_spin_lock(&sync_lock); max_warp = max(max_warp, prev - now); + /* + * Check whether this bounces back and forth. Only + * one CPU should observe time going backwards. + */ + if (cur_warps != nr_warps) + random_warps++; nr_warps++; + cur_warps = nr_warps; arch_spin_unlock(&sync_lock); } } @@ -160,6 +168,8 @@ void check_tsc_sync_source(int cpu) smp_processor_id(), cpu); pr_warning("Measured %Ld cycles TSC warp between CPUs, " "turning off TSC clock.\n", max_warp); + if (random_warps) + pr_warning("TSC warped randomly between CPUs\n"); mark_tsc_unstable("check_tsc_sync_source failed"); } else { pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n", @@ -170,6 +180,7 @@ void check_tsc_sync_source(int cpu) * Reset it - just in case we boot another CPU later: */ atomic_set(&start_count, 0); + random_warps = 0; nr_warps = 0; max_warp = 0; last_tsc = 0;