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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0FB44C531C9 for ; Fri, 24 Jul 2026 04:46:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=X/GJvTUB0Fc/V+y5K6V4KuOXG7ykfjR54qQ9NpMgq5k=; b=xHeVq2cmhu/GqyqvEt5NWEVxDj Hr9KOs0OsWCjPJO58iGp4y2/jIqD+mIPpigfXXzDYgW4FDj3lFGOx+vTWq0GEM+eXM4gDwoPoehQx nO6R9KWmUSdfnNxK8g/Cih9ZfQPu6ch280j9oGRnOlC01MLe78a7tpuCBxhZ66Q/7y45Im5xeg6Yp BDDPjD1goUa1pj4VQD3dPXRGGen/VS29E5qKiroKT2sRFA3ysnWKR/qB5KCCDiFPlOYE9Y3II+1/1 uWpFIxuBSJ+gIRQv87GoCPMAtqNfCR23VJG02WUBRwC7qiUnPA5cycH0jzCZEb9an4SuTBPtzmc1p M0RpUvvw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wn7nZ-0000000FTXi-3zo7; Fri, 24 Jul 2026 04:46:13 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wn7nX-0000000FTXI-3Wsk for linux-arm-kernel@lists.infradead.org; Fri, 24 Jul 2026 04:46:12 +0000 Received: from [192.168.0.105] (unknown [4.194.122.170]) by linux.microsoft.com (Postfix) with ESMTPSA id 9998920B7167; Thu, 23 Jul 2026 21:45:52 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 9998920B7167 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1784868356; bh=X/GJvTUB0Fc/V+y5K6V4KuOXG7ykfjR54qQ9NpMgq5k=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=swgSdo9KScjxK2OqSJz8QOxqkfGxp4gXfakbWLqh8l3CT7QKquoToCBKsmB0bvG9m 0FKB4YCtb1VHT1C38M/FPHAIe0j+PbLP0xfoqdrF8gvhisMP8gAZNuZZN/90BTqDGG zzV/TK3wmTWMVsTRTjI/f7YVxKsEzAwWsgWpIy+I= Message-ID: Date: Fri, 24 Jul 2026 10:16:03 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: smp: distinguish secondary CPUs that hang after reaching head.S To: Anshuman Khandual , Jinjie Ruan , Catalin Marinas , Will Deacon Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Marc Zyngier , Thomas Huth , Fuad Tabba , Thomas Gleixner , Pengjie Zhang , mrigendrachaubey , Saurabh Sengar References: <20260722113044.1835365-1-namjain@linux.microsoft.com> <6e13c10f-ccc2-48c3-bf8a-d65133a33e17@huawei.com> <70e8596f-7316-4cc9-90e8-ff06a94c4616@arm.com> Content-Language: en-US From: Naman Jain In-Reply-To: <70e8596f-7316-4cc9-90e8-ff06a94c4616@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260723_214611_939590_63227AAC X-CRM114-Status: GOOD ( 17.58 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 7/23/2026 11:26 AM, Anshuman Khandual wrote: > > > On 23/07/26 8:19 AM, Jinjie Ruan wrote: >> >> 在 2026/7/22 19:30, Naman Jain 写道: >>> When a secondary CPU fails to come online, __cpu_up() falls back to >>> __early_cpu_boot_status, but boot status 0x0 is ambiguous: it cannot >>> distinguish a CPU that never executed head.S (firmware/hypervisor never >>> dispatched it, so it never ran a single instruction) from one that >>> entered head.S, started executing, and then got stuck somewhere in kernel >>> bring-up. Add a change to let us tell those two cases apart, which >>> narrows down where to look when a CPU goes missing during boot. >> I previously encountered this issue when debugging the parallel startup >> of ARM64 secondary cores. It is difficult for the kernel to determine >> whether the secondary core is hung in the firmware or whether it has not >> executed a single instruction. So I think this motive is reasonable. > > Why should kernel determine the difference here ? Would not the firmware > know if it has started any secondary CPU for the kernel which must have > come inside head.S ? If the cpu gets hung inside firmware while starting > up then the debug responsibilities belong there instead. > > Still wondering what's the rationale for this change. Hello Anshuman, This sounds fair to me. Let me elaborate the problem, beyond the scope of this patch. In production, we occasionally see these crashes where one of the CPU fails to bring up online, with 0x0 status code. Hypervisor may be missing the telemetry, but the problem is that we don't know if the secondary CPU ever started executing the instructions or is stuck somewhere between the start of head.S and marking itself online at the end of secondary_start_kernel(). There are couple of places, where we get those other status codes, but not everywhere. If the issue is not easily reproducible, experiments on local setups do not yield anything. That's where I am attempting to add some more information in kernel to debug these issues. Regards, Naman