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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable 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 D3D4FC433DF for ; Sun, 31 May 2020 18:26:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B6BAB20810 for ; Sun, 31 May 2020 18:26:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728361AbgEaS0U (ORCPT ); Sun, 31 May 2020 14:26:20 -0400 Received: from mx2.suse.de ([195.135.220.15]:52384 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727084AbgEaS0P (ORCPT ); Sun, 31 May 2020 14:26:15 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 9586EACE3; Sun, 31 May 2020 18:26:14 +0000 (UTC) From: Giovanni Gherdovich To: Srinivas Pandruvada , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Borislav Petkov , "Rafael J . Wysocki" Cc: x86@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Ricardo Neri , Giovanni Gherdovich Subject: [PATCH v2 1/3] x86, sched: check for counters overflow in frequency invariant accounting Date: Sun, 31 May 2020 20:24:51 +0200 Message-Id: <20200531182453.15254-2-ggherdovich@suse.cz> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20200531182453.15254-1-ggherdovich@suse.cz> References: <20200531182453.15254-1-ggherdovich@suse.cz> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The product mcnt * arch_max_freq_ratio can overflows u64. For context, a large value for arch_max_freq_ratio would be 5000, corresponding to a turbo_freq/base_freq ratio of 5 (normally it's more like 1500-2000). A large increment frequency for the MPERF counter would be 5GHz (the base clock of all CPUs on the market today is less than that). With these figures, a CPU would need to go without a scheduler tick for around 8 days for the u64 overflow to happen. It is unlikely, but the check is warranted. Under similar conditions, the difference acnt of two consecutive APERF readings can overflow as well. In these circumstances is appropriate to disable frequency invariant accounting: the feature relies on measures of the clock frequency done at every scheduler tick, which need to be "fresh" to be at all meaningful. A note on i386: prior to version 5.1, the GCC compiler didn't have the builtin function __builtin_mul_overflow. In these GCC versions the macro check_mul_overflow needs __udivdi3() to do (u64)a/b, which the kernel doesn't provide. For this reason this change fails to build on i386 if GCC<5.1, and we protect the entire frequency invariant code behind CONFIG_X86_64 (special thanks to "kbuild test robot" ). Signed-off-by: Giovanni Gherdovich Signed-off-by: Peter Zijlstra (Intel) Fixes: 1567c3e3467c ("x86, sched: Add support for frequency invariance") --- arch/x86/include/asm/topology.h | 2 +- arch/x86/kernel/smpboot.c | 33 ++++++++++++++++++++++++++++----- 2 files changed, 29 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h index 79d8d5496330..f4234575f3fd 100644 --- a/arch/x86/include/asm/topology.h +++ b/arch/x86/include/asm/topology.h @@ -193,7 +193,7 @@ static inline void sched_clear_itmt_support(void) } #endif /* CONFIG_SCHED_MC_PRIO */ -#ifdef CONFIG_SMP +#if defined(CONFIG_SMP) && defined(CONFIG_X86_64) #include DECLARE_STATIC_KEY_FALSE(arch_scale_freq_key); diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 2f24c334a938..d660966d7de7 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -55,6 +55,7 @@ #include #include #include +#include #include #include @@ -1777,6 +1778,7 @@ void native_play_dead(void) #endif +#ifdef CONFIG_X86_64 /* * APERF/MPERF frequency ratio computation. * @@ -2047,11 +2049,19 @@ static void init_freq_invariance(bool secondary) } } +static void disable_freq_invariance_workfn(struct work_struct *work) +{ + static_branch_disable(&arch_scale_freq_key); +} + +static DECLARE_WORK(disable_freq_invariance_work, + disable_freq_invariance_workfn); + DEFINE_PER_CPU(unsigned long, arch_freq_scale) = SCHED_CAPACITY_SCALE; void arch_scale_freq_tick(void) { - u64 freq_scale; + u64 freq_scale = SCHED_CAPACITY_SCALE; u64 aperf, mperf; u64 acnt, mcnt; @@ -2063,19 +2073,32 @@ void arch_scale_freq_tick(void) acnt = aperf - this_cpu_read(arch_prev_aperf); mcnt = mperf - this_cpu_read(arch_prev_mperf); - if (!mcnt) - return; this_cpu_write(arch_prev_aperf, aperf); this_cpu_write(arch_prev_mperf, mperf); - acnt <<= 2*SCHED_CAPACITY_SHIFT; - mcnt *= arch_max_freq_ratio; + if (check_shl_overflow(acnt, 2*SCHED_CAPACITY_SHIFT, &acnt)) + goto error; + + if (check_mul_overflow(mcnt, arch_max_freq_ratio, &mcnt) || !mcnt) + goto error; freq_scale = div64_u64(acnt, mcnt); + if (!freq_scale) + goto error; if (freq_scale > SCHED_CAPACITY_SCALE) freq_scale = SCHED_CAPACITY_SCALE; this_cpu_write(arch_freq_scale, freq_scale); + return; + +error: + pr_warn("Scheduler frequency invariance went wobbly, disabling!\n"); + schedule_work(&disable_freq_invariance_work); +} +#else +static inline void init_freq_invariance(bool secondary) +{ } +#endif /* CONFIG_X86_64 */ -- 2.16.4