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[2620:137:e000::1:20]) by mx.google.com with ESMTP id e12-20020a056402190c00b0045154775089si9947564edz.625.2022.11.21.07.18.11; Mon, 21 Nov 2022 07:18:59 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linutronix.de header.s=2020 header.b=PgiWo0S6; dkim=neutral (no key) header.i=@linutronix.de header.s=2020e; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=linutronix.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232202AbiKUPON (ORCPT + 99 others); Mon, 21 Nov 2022 10:14:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38212 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232112AbiKUPNr (ORCPT ); Mon, 21 Nov 2022 10:13:47 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E690C68AE; Mon, 21 Nov 2022 07:08:05 -0800 (PST) Date: Mon, 21 Nov 2022 15:08:02 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1669043283; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3zpF293Xpb7hIE7qRypmxo8y68aTytICJY5A2Ecegdw=; b=PgiWo0S6xD9BH70LrjHvg5GV7A8twZdSSy4NKAREw/12JyDOD5RNhx6NrAwuOqC6oYbWTv nx4dsYgEjL9qSUMfoPjaziL7lnJJDNx5qRCXwtmaaxiL98tM0zXctNkVqtQxDdGBHTfveb SbjfXL3Fj3Gdcs+6pMuHIUwmrVjH6lvCikR8E1G1xvLnMYZzsZCwyQI9QfdM9IjCCEN5uz nBFOyEPx7QwK/xuCIxNsdmoOc32XDemDNviVeahiYPnnpPQpyzUv9pxfhbrxwMsikvXv8L 7rqzVROvqn5lxJTkm3SQ2FYAWWSGMoCHZqkax7AAiNsJ+bYnM9/xvVG6XGa6Dw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1669043283; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3zpF293Xpb7hIE7qRypmxo8y68aTytICJY5A2Ecegdw=; b=RzKT1lqsFcNODbUbO1UPa0SX9OBj6rxz0/WyK3/IAH3K9/Of2+0Yzc5glmPZScPF6BooRn IzPknonxlDPUP7BA== From: "tip-bot2 for Joe Korty" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: timers/urgent] clocksource/drivers/arm_arch_timer: Fix XGene-1 TVAL register math error Cc: Joe Korty , Marc Zyngier , Thomas Gleixner , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20221024165422.GA51107@zipoli.concurrent-rt.com> References: <20221024165422.GA51107@zipoli.concurrent-rt.com> MIME-Version: 1.0 Message-ID: <166904328202.4906.4328519083119189817.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1750119418047009845?= X-GMAIL-MSGID: =?utf-8?q?1750119418047009845?= The following commit has been merged into the timers/urgent branch of tip: Commit-ID: 839a973988a94c15002cbd81536e4af6ced2bd30 Gitweb: https://git.kernel.org/tip/839a973988a94c15002cbd81536e4af6ced2bd30 Author: Joe Korty AuthorDate: Mon, 21 Nov 2022 14:53:43 Committer: Thomas Gleixner CommitterDate: Mon, 21 Nov 2022 16:01:56 +01:00 clocksource/drivers/arm_arch_timer: Fix XGene-1 TVAL register math error The TVAL register is 32 bit signed. Thus only the lower 31 bits are available to specify when an interrupt is to occur at some time in the near future. Attempting to specify a larger interval with TVAL results in a negative time delta which means the timer fires immediately upon being programmed, rather than firing at that expected future time. The solution is for Linux to declare that TVAL is a 31 bit register rather than give its true size of 32 bits. This prevents Linux from programming TVAL with a too-large value. Note that, prior to 5.16, this little trick was the standard way to handle TVAL in Linux, so there is nothing new happening here on that front. The softlockup detector hides the issue, because it keeps generating short timer deadlines that are within the scope of the broken timer. Disabling it, it starts using NO_HZ with much longer timer deadlines, which turns into an interrupt flood: 11: 1124855130 949168462 758009394 76417474 104782230 30210281 310890 1734323687 GICv2 29 Level arch_timer And "much longer" isn't that long: it takes less than 43s to underflow TVAL at 50MHz (the frequency of the counter on XGene-1). Some comments on the v1 version of this patch by Marc Zyngier: XGene implements CVAL (a 64bit comparator) in terms of TVAL (a countdown register) instead of the other way around. TVAL being a 32bit register, the width of the counter should equally be 32. However, TVAL is a *signed* value, and keeps counting down in the negative range once the timer fires. It means that any TVAL value with bit 31 set will fire immediately, as it cannot be distinguished from an already expired timer. Reducing the timer range back to a paltry 31 bits papers over the issue. Another problem cannot be fixed though, which is that the timer interrupt *must* be handled within the negative countdown period, or the interrupt will be lost (TVAL will rollover to a positive value, indicative of a new timer deadline). Fixes: 012f18850452 ("clocksource/drivers/arm_arch_timer: Work around broken CVAL implementations") Signed-off-by: Joe Korty Signed-off-by: Marc Zyngier Signed-off-by: Thomas Gleixner Reviewed-by: Marc Zyngier Link: https://lore.kernel.org/r/20221024165422.GA51107@zipoli.concurrent-rt.com Link: https://lore.kernel.org/r/20221121145343.896018-1-maz@kernel.org [maz: revamped the commit message] --- drivers/clocksource/arm_arch_timer.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c index a7ff775..933bb96 100644 --- a/drivers/clocksource/arm_arch_timer.c +++ b/drivers/clocksource/arm_arch_timer.c @@ -806,6 +806,9 @@ static u64 __arch_timer_check_delta(void) /* * XGene-1 implements CVAL in terms of TVAL, meaning * that the maximum timer range is 32bit. Shame on them. + * + * Note that TVAL is signed, thus has only 31 of its + * 32 bits to express magnitude. */ MIDR_ALL_VERSIONS(MIDR_CPU_MODEL(ARM_CPU_IMP_APM, APM_CPU_PART_POTENZA)), @@ -813,8 +816,8 @@ static u64 __arch_timer_check_delta(void) }; if (is_midr_in_range_list(read_cpuid_id(), broken_cval_midrs)) { - pr_warn_once("Broken CNTx_CVAL_EL1, limiting width to 32bits"); - return CLOCKSOURCE_MASK(32); + pr_warn_once("Broken CNTx_CVAL_EL1, using 31 bit TVAL instead.\n"); + return CLOCKSOURCE_MASK(31); } #endif return CLOCKSOURCE_MASK(arch_counter_get_width());