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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 5A0E5C433C1 for ; Tue, 30 Mar 2021 08:26:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 228E86157F for ; Tue, 30 Mar 2021 08:26:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231318AbhC3IZ7 (ORCPT ); Tue, 30 Mar 2021 04:25:59 -0400 Received: from mga12.intel.com ([192.55.52.136]:18303 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231220AbhC3IZz (ORCPT ); Tue, 30 Mar 2021 04:25:55 -0400 IronPort-SDR: CHkaCXplw95aptKXGVOenHqMBwsDvguAJ4v7ebE/wVAFRRSBJjCyhA6V8RmeNz0Oxj8XxbzhN7 mvBIycP1nloA== X-IronPort-AV: E=McAfee;i="6000,8403,9938"; a="171123246" X-IronPort-AV: E=Sophos;i="5.81,290,1610438400"; d="scan'208";a="171123246" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Mar 2021 01:25:54 -0700 IronPort-SDR: 4zIcgBhM42pzRnspE8FyKlh5H8rhzmN1MtIm3g0XvpqCDD39Lm4UHzyo5ljSD30xoT16R91Y4s HcNXHuvO6dzQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.81,290,1610438400"; d="scan'208";a="411500993" Received: from shbuild999.sh.intel.com ([10.239.147.94]) by fmsmga008.fm.intel.com with ESMTP; 30 Mar 2021 01:25:51 -0700 From: Feng Tang To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H . Peter Anvin" , Peter Zijlstra , x86@kernel.org, linux-kernel@vger.kernel.org Cc: rui.zhang@intel.com, andi.kleen@intel.com, dave.hansen@intel.com, len.brown@intel.com, Feng Tang Subject: [RFC 2/2] x86/tsc: mark tsc reliable for qualified platforms Date: Tue, 30 Mar 2021 16:25:47 +0800 Message-Id: <1617092747-15769-2-git-send-email-feng.tang@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1617092747-15769-1-git-send-email-feng.tang@intel.com> References: <1617092747-15769-1-git-send-email-feng.tang@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There are cases that tsc clocksource are wrongly judged as unstable by clocksource watchdogs like hpet, acpi_pm or 'refined-jiffies'. While there is hardly a general reliable way to check the validity of a watchdog, and to protect the innocent tsc, Thomas Gleixner proposed [1]: "I'm inclined to lift that requirement when the CPU has: 1) X86_FEATURE_CONSTANT_TSC 2) X86_FEATURE_NONSTOP_TSC 3) X86_FEATURE_NONSTOP_TSC_S3 4) X86_FEATURE_TSC_ADJUST 5) At max. 4 sockets After two decades of horrors we're finally at a point where TSC seems to be halfway reliable and less abused by BIOS tinkerers. TSC_ADJUST was really key as we can now detect even small modifications reliably and the important point is that we can cure them as well (not pretty but better than all other options)." As feature #3 X86_FEATURE_NONSTOP_TSC_S3 only exists on several generations of Atom processor, and is always coupled with X86_FEATURE_CONSTANT_TSC and X86_FEATURE_NONSTOP_TSC, skip checking it,. and also be more defensive to use maxim of 2 sockets. The check is done inside tsc_init() before registering 'tsc-early' and 'tsc' clocksources, as there were cases that both of them had been wrongly judged as unreliable. Another idea is to not lift the check here, but inside the tsc_sync_check_timer, stop the clocksource watchdog timer if there is no TSC_ADJUST overridden found in 10 minutes after boot. [1]. https://lore.kernel.org/lkml/87eekfk8bd.fsf@nanos.tec.linutronix.de/ Suggested-by: Thomas Gleixner Signed-off-by: Feng Tang --- arch/x86/kernel/tsc.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index f70dffc..3a451e3 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1193,6 +1193,17 @@ static void __init check_system_tsc_reliable(void) #endif if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) tsc_clocksource_reliable = 1; + + /* + * Ideally the socket number should be checked, but this is called + * by tsc_init() which is in early boot phase and the socket numbers + * may not be available. Use 'nr_online_nodes' as a fallback solution + */ + if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && + boot_cpu_has(X86_FEATURE_NONSTOP_TSC) && + boot_cpu_has(X86_FEATURE_TSC_ADJUST) && + nr_online_nodes <= 2) + tsc_clocksource_reliable = 1; } /* -- 2.7.4