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 9F2A7F589A4 for ; Thu, 23 Apr 2026 12:32:56 +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=fo94b7MqFfTgDj99SSJRoVZ8tjQmbwLpsx6plvLcAHM=; b=tnK3SC0fpvaR85FQiVDQmvlpC3 4GTiltzKXFryTRoKUKmWxyL4DYw/jlQ6yAvSBRDX+Pmt8fdnNe7EeMf9Pqy6StVdzmntSkpgzI5cU bfrkbu/Xj7HS+aTRBsn1KSQ7zcOp8NdemTjTsLvx0sH0TuzTNgt0ARqTSp5u/UMdnlb9Gnmg/+aSg kQnhwSVZclli+9YqcF/1IR4s+35E9Aah+6gQuJHPU4rRVTv072rm/RC9aaMQ+uh5nb/nv99gTa4W8 Wzsz3hxXXTcyFh+aCv27t4GmxNNGnV4XfYz8WSZouCqBb2uO9r1fDXxx7sJMj9jWsX2MwSBqak/GD ydNA/rDw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wFtEf-0000000BcbO-2wJ8; Thu, 23 Apr 2026 12:32:49 +0000 Received: from canpmsgout09.his.huawei.com ([113.46.200.224]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1wFtEZ-0000000Bcac-15r0 for linux-arm-kernel@lists.infradead.org; Thu, 23 Apr 2026 12:32:48 +0000 dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=fo94b7MqFfTgDj99SSJRoVZ8tjQmbwLpsx6plvLcAHM=; b=vek5LSEiClJIzXVuYeoZz7x2S2Tdsogj999dQK1WVA07tF3DQcFMWfs0U3I4hSuXRPdV6cwnl oh77IPF8Sf0Fm2pOh7U+7Dij9xeYsbipUZb9EuHXcEPZg7Tg58IlMf3jOruAIY9VdCYwiRNtbpQ COep4lW3SCwS/mz1FuWqW7Q= Received: from mail.maildlp.com (unknown [172.19.163.127]) by canpmsgout09.his.huawei.com (SkyGuard) with ESMTPS id 4g1b0z6Wksz1cyPZ; Thu, 23 Apr 2026 20:26:11 +0800 (CST) Received: from dggpemf500011.china.huawei.com (unknown [7.185.36.131]) by mail.maildlp.com (Postfix) with ESMTPS id 729E1402AB; Thu, 23 Apr 2026 20:32:34 +0800 (CST) Received: from [10.67.109.254] (10.67.109.254) by dggpemf500011.china.huawei.com (7.185.36.131) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Thu, 23 Apr 2026 20:32:33 +0800 Message-ID: <78515da3-03a1-4fdb-a606-3fea9f4cd20b@huawei.com> Date: Thu, 23 Apr 2026 20:32:34 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] cpu/hotplug: Fix NULL kobject warning in cpuhp_smt_enable() To: Thomas Gleixner , Catalin Marinas CC: , , , , , , James Morse , References: <20260417075534.3745793-1-ruanjinjie@huawei.com> <87ldee0z1w.ffs@tglx> From: Jinjie Ruan In-Reply-To: <87ldee0z1w.ffs@tglx> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.109.254] X-ClientProxiedBy: kwepems100002.china.huawei.com (7.221.188.206) To dggpemf500011.china.huawei.com (7.185.36.131) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260423_053243_977282_14CE61B9 X-CRM114-Status: GOOD ( 19.84 ) 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 4/23/2026 6:08 PM, Thomas Gleixner wrote: > On Sat, Apr 18 2026 at 12:55, Catalin Marinas wrote: >> Another option would have been to avoid marking such CPUs present but I >> think this will break other things. Yet another option is to register >> all CPU devices even if they never come up (like maxcpus greater than >> actual CPUs). >> >> Opinions? It might be an arm64+ACPI-only thing. > > I think so. The proper thing to do is to apply sane limits: > > 1) The possible CPUs enumerated by firmware N_POSSIBLE_FW > > 2) The maxcpus limit on the command line N_MAXCPUS_CL > > So the actual possible CPUs evaluates to: > > num_possible = min(N_POSSIBLE_FW, N_MAXCPUS_CL, CONFIG_NR_CPUS); > > The evaluation of the firmware should not mark CPUs present which are > actually not. ACPI gives you that information. See: > > 5.2.12.14 GIC CPU Interface (GICC) Structure > > in the ACPI spec. That has two related bits: > > Enabled: > > If this bit is set, the processor is ready for use. If this bit is > clear and the Online Capable bit is set, the system supports enabling > this processor during OS runtime. If this bit is clear and the Online > Capable bit is also clear, this processor is un- usable, and the > operating system support will not attempt to use it. > > Online Capable: > > The information conveyed by this bit depends on the value of the > Enabled bit. If the Enabled bit is set, this bit is reserved and must > be zero. Otherwise, if this bit is set, the system supports enabling > this processor later during OS runtime > > So the combination of those gives you the right answer: > > Enabled Online > Capable > 0 0 Not present, not possible > 0 1 Not present, but possible to "hotplug" layter > 1 0 Present > 1 1 Invalid On x86, it seems that all CPUs with the ACPI_MADT_ENABLED bit set will be marked as present. acpi_parse_x2apic() -> enabled = processor->lapic_flags & ACPI_MADT_ENABLED -> topology_register_apic(enabled) -> topo_register_apic(enabled) -> set_cpu_present(cpu, true) > > The kernel sizes everything on the number of possible CPUs and the > present CPU mask is only there to figure out which CPUs are actually > usable and can be brought up. > > The runtime physical hotplug mechanics use acpi_[un]map_cpu() to toggle > the present bit. > > Thanks, > > tglx > > >