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 141D0C55182 for ; Wed, 5 Aug 2026 04:42:29 +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=wocs7BrvMROfC3flwkNIJADWZwICYt4AX965blqbLWs=; b=TUElNA+F/yDaFMZlAHg8PfyG1m 8Ulm4uXEY/WNnJVnrrfMuvJS6AaI4U1k5J5PquGpaFh2Nj9h2XsaDwVduBU4ATLfTecTvpOCix0H3 UPwnWaCoRSwdcrEfDdBB6fe4W+X2vgmMPUrYGcbTQ0NuqYnTnENbH6MiWgX3Vg7m0RX5afFgMU/B1 ZT9lv7A4b3Nvoqt270p+neElDnJptbw9hu10ZCQklSIM4PziamuuuYm4xf0DPzzpBv/5eahHDEBXF 9NA9PHA5LD8bd1kzGjgP2g/9dlYh6xmtk8dnFuugsD35GPi4SzXKXT9B0mt1tQx6nioPC6aQ2BbDG 1NAgvEkQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wrTSJ-00000003EA3-4Azr; Wed, 05 Aug 2026 04:42:15 +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 1wrTSI-00000003E9g-0Bqq for linux-arm-kernel@lists.infradead.org; Wed, 05 Aug 2026 04:42:15 +0000 Received: from [10.7.58.6] (unknown [4.194.122.170]) by linux.microsoft.com (Postfix) with ESMTPSA id 7BD1820B7169; Tue, 4 Aug 2026 21:41:47 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 7BD1820B7169 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1785904910; bh=wocs7BrvMROfC3flwkNIJADWZwICYt4AX965blqbLWs=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Qq9IGe1F+8af8fGOOGD6lh0x6Zi02G2paZfbSpLeJVFDhpCnZ1RN357zA61P57joS +i6Iw0maX5wy5xKIYYY+aj/qy4UDGSdu0XL0Gtdk817s1e9SzqVzIgoRTNqF9ei+q1 BWznAJyNiLNtQCmO8lRtf06JCHM0qOWrl92dFkcQ= Message-ID: <96bf067f-b811-4a25-a7d3-ff50c13134d0@linux.microsoft.com> Date: Wed, 5 Aug 2026 10:12:03 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: smp: distinguish secondary CPUs that hang after reaching head.S To: Will Deacon Cc: Anshuman Khandual , Jinjie Ruan , Catalin Marinas , 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> <45ab9640-14b7-48d7-89e2-109aa3935539@linux.microsoft.com> Content-Language: en-US From: Naman Jain In-Reply-To: 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-20260804_214214_114618_4F02B6E2 X-CRM114-Status: GOOD ( 21.45 ) 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 8/4/2026 7:13 PM, Will Deacon wrote: > On Mon, Jul 27, 2026 at 11:08:05AM +0530, Naman Jain wrote: >> On 7/26/2026 7:16 PM, Will Deacon wrote: >>> On Fri, Jul 24, 2026 at 10:16:03AM +0530, Naman Jain wrote: >>>> 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. >>> >>> I think this is a game of diminishing returns. There's a lot of stuff >>> that the firmware/hypervisor can get wrong here and trying to detect or >>> handle that in Linux is going to be a real mess. For example, if it >>> enters the kernel at the wrong address, or in the wrong mode, or with >>> the MMU enabled etc. It sounds like you don't have much idea about >>> what happens in the failure case, so it might not even execute the code >>> that you're adding correctly. >> >> That is true. I agree. While we cannot and should not worry about adding >> logs for each of these firmware failure points in kernel, do you see any >> merit in adding any of this information to the kernel to at least narrow >> down the problem? > > Possibly, but I'd prefer to land the parallel bringup work first and then > see whether this still makes sense. > > Will Acked. Regards, Naman