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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 33BF1C32771 for ; Sun, 18 Sep 2022 14:00:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229609AbiIROAQ (ORCPT ); Sun, 18 Sep 2022 10:00:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46020 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229533AbiIROAP (ORCPT ); Sun, 18 Sep 2022 10:00:15 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8B97515A12; Sun, 18 Sep 2022 07:00:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=KeyHnDwtz03NUIbQKH0mlcSz0RqoE8e8mbmPZs7mkVU=; b=GyOYQyWwt07jEidfRgym5hfyeF Z4VYyLbUDS88clnJfP6wT0v8u9Gms5C6knDRu2rd8MMCgTFaB4VWuaWyaIp2gbnvvbH9zpXzZ8+uD xmj4oh/KWun0X4Nq1P3vat9RDKcGAXckDahHA1MaAmjhznR4AjwuNzJdLVWv6+5ZTb/S8iINUA/Ml oX+h7kLt+O5SEPLkMCwAGYqSAMbNdJQOTikSXqr3LZSL+1lYRtQAvRtuSwl9ZpbxIZyPLm419tv7n w9swsXuoBv0tfQG23yq1NaMCcKnfM8mPLX74wNC5L3jNPbiqyiU6lMUxLiYd6lcF7MRVq/n58xRDE AOb6wX9Q==; Received: from 201-27-35-168.dsl.telesp.net.br ([201.27.35.168] helo=[192.168.1.60]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1oZup8-0080cc-ON; Sun, 18 Sep 2022 15:59:06 +0200 Message-ID: Date: Sun, 18 Sep 2022 10:58:34 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH V3 01/11] ARM: Disable FIQs (but not IRQs) on CPUs shutdown paths Content-Language: en-US To: Russell King , Marc Zyngier , linux-arm-kernel@lists.infradead.org, will@kernel.org, Mark Rutland , arnd@arndb.de, Catalin Marinas Cc: kexec@lists.infradead.org, pmladek@suse.com, bhe@redhat.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, netdev@vger.kernel.org, x86@kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, halves@canonical.com, fabiomirmar@gmail.com, alejandro.j.jimenez@oracle.com, andriy.shevchenko@linux.intel.com, bp@alien8.de, corbet@lwn.net, d.hatayama@jp.fujitsu.com, dave.hansen@linux.intel.com, dyoung@redhat.com, feng.tang@intel.com, gregkh@linuxfoundation.org, mikelley@microsoft.com, hidehiro.kawai.ez@hitachi.com, jgross@suse.com, john.ogness@linutronix.de, keescook@chromium.org, luto@kernel.org, mhiramat@kernel.org, mingo@redhat.com, paulmck@kernel.org, peterz@infradead.org, rostedt@goodmis.org, senozhatsky@chromium.org, stern@rowland.harvard.edu, tglx@linutronix.de, vgoyal@redhat.com, vkuznets@redhat.com, xuqiang36@huawei.com References: <20220819221731.480795-1-gpiccoli@igalia.com> <20220819221731.480795-2-gpiccoli@igalia.com> From: "Guilherme G. Piccoli" In-Reply-To: <20220819221731.480795-2-gpiccoli@igalia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On 19/08/2022 19:17, Guilherme G. Piccoli wrote: > Currently the regular CPU shutdown path for ARM disables IRQs/FIQs > in the secondary CPUs - smp_send_stop() calls ipi_cpu_stop(), which > is responsible for that. IRQs are architecturally masked when we > take an interrupt, but FIQs are high priority than IRQs, hence they > aren't masked. With that said, it makes sense to disable FIQs here, > but there's no need for (re-)disabling IRQs. > > More than that: there is an alternative path for disabling CPUs, > in the form of function crash_smp_send_stop(), which is used for > kexec/panic path. This function relies on a SMP call that also > triggers a busy-wait loop [at machine_crash_nonpanic_core()], but > without disabling FIQs. This might lead to odd scenarios, like > early interrupts in the boot of kexec'd kernel or even interrupts > in secondary "disabled" CPUs while the main one still works in the > panic path and assumes all secondary CPUs are (really!) off. > > So, let's disable FIQs in both paths and *not* disable IRQs a second > time, since they are already masked in both paths by the architecture. > This way, we keep both CPU quiesce paths consistent and safe. > > Cc: Marc Zyngier > Cc: Michael Kelley > Cc: Russell King > Signed-off-by: Guilherme G. Piccoli > > --- > > V3: > - No changes. > > V2: > - Small wording improvement (thanks Michael Kelley); > - Only disable FIQs, since IRQs are masked by architecture > definition when we take an interrupt. Thanks a lot Russell > and Marc for the discussion [0]. > > Should we add a Fixes tag here? If so, maybe the proper target is: > b23065313297 ("ARM: 6522/1: kexec: Add call to non-crashing cores through IPI") > > [0] https://lore.kernel.org/lkml/Ymxcaqy6DwhoQrZT@shell.armlinux.org.uk/ > > > arch/arm/kernel/machine_kexec.c | 2 ++ > arch/arm/kernel/smp.c | 5 ++--- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c > index f567032a09c0..0b482bcb97f7 100644 > --- a/arch/arm/kernel/machine_kexec.c > +++ b/arch/arm/kernel/machine_kexec.c > @@ -77,6 +77,8 @@ void machine_crash_nonpanic_core(void *unused) > { > struct pt_regs regs; > > + local_fiq_disable(); > + > crash_setup_regs(®s, get_irq_regs()); > printk(KERN_DEBUG "CPU %u will stop doing anything useful since another CPU has crashed\n", > smp_processor_id()); > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c > index 978db2d96b44..36e6efad89f3 100644 > --- a/arch/arm/kernel/smp.c > +++ b/arch/arm/kernel/smp.c > @@ -600,6 +600,8 @@ static DEFINE_RAW_SPINLOCK(stop_lock); > */ > static void ipi_cpu_stop(unsigned int cpu) > { > + local_fiq_disable(); > + > if (system_state <= SYSTEM_RUNNING) { > raw_spin_lock(&stop_lock); > pr_crit("CPU%u: stopping\n", cpu); > @@ -609,9 +611,6 @@ static void ipi_cpu_stop(unsigned int cpu) > > set_cpu_online(cpu, false); > > - local_fiq_disable(); > - local_irq_disable(); > - > while (1) { > cpu_relax(); > wfe(); [+CC all ARM folks I could find] Hi folks, sorry for the ping. Any reviews are greatly appreciated in this one - this is the V3 of the series but I never got any specific review for this patch. Based on a previous discussion with Russell and Marc [0], seems this one makes sense and fixes an inconsistency related to kdump/panic. Really appreciate reviews or at least some indication on which path I should take to get this potentially merged. Cheers, Guilherme [0] https://lore.kernel.org/lkml/Ymxcaqy6DwhoQrZT@shell.armlinux.org.uk/