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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1E209C10F27 for ; Wed, 11 Mar 2020 12:40:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E651C208E4 for ; Wed, 11 Mar 2020 12:40:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729403AbgCKMkJ (ORCPT ); Wed, 11 Mar 2020 08:40:09 -0400 Received: from mail.cn.fujitsu.com ([183.91.158.132]:23511 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729383AbgCKMkI (ORCPT ); Wed, 11 Mar 2020 08:40:08 -0400 X-IronPort-AV: E=Sophos;i="5.70,540,1574092800"; d="scan'208";a="86170022" Received: from unknown (HELO cn.fujitsu.com) ([10.167.33.5]) by heian.cn.fujitsu.com with ESMTP; 11 Mar 2020 20:39:37 +0800 Received: from G08CNEXMBPEKD06.g08.fujitsu.local (unknown [10.167.33.206]) by cn.fujitsu.com (Postfix) with ESMTP id E669850A9980; Wed, 11 Mar 2020 20:29:38 +0800 (CST) Received: from [10.167.226.60] (10.167.226.60) by G08CNEXMBPEKD06.g08.fujitsu.local (10.167.33.206) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Wed, 11 Mar 2020 20:39:35 +0800 Subject: Re: Is this code chunk in init_apic_mappings() superfluous? To: Thomas Gleixner , X86 ML , LKML CC: Ingo Molnar , Borislav Petkov References: <978293b9-8e9f-55f6-6ec4-e2d66c4db0de@cn.fujitsu.com> <87imjg9zgp.fsf@nanos.tec.linutronix.de> From: Cao jin Message-ID: <3859d094-676d-7e17-0655-9d0091a0d47c@cn.fujitsu.com> Date: Wed, 11 Mar 2020 20:39:37 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <87imjg9zgp.fsf@nanos.tec.linutronix.de> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.60] X-ClientProxiedBy: G08CNEXCHPEKD05.g08.fujitsu.local (10.167.33.203) To G08CNEXMBPEKD06.g08.fujitsu.local (10.167.33.206) X-yoursite-MailScanner-ID: E669850A9980.A881E X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: caoj.fnst@cn.fujitsu.com Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/7/20 7:27 PM, Thomas Gleixner wrote: > Cao jin writes: >> Hi, >> >> I am trying to figure the following code chunk out: >> >> if (x2apic_mode) { >> boot_cpu_physical_apicid = read_apic_id(); >> return; >> } >> >> As my understanding, even in x2APIC mode, boot_cpu_physical_apicid is >> also got via early_acpi_process_madt --> ... --> register_lapic_address, >> so, is it for any corner case I am not aware? > > The case when there are neither ACPI nor valid mptables. Unlikely, but > possible in theory. > I noticed this case in its calling comments, but failed to associate it with a x2APIC... So init_apic_mapping() is for 2 corner cases that doesn't map APIC register before: one you mentioned here, and MP default configuration the other. Thanks Thomas. -- Sincerely, Cao jin