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 3FB76C3A5A9 for ; Mon, 4 May 2020 14:54:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 29E41206B9 for ; Mon, 4 May 2020 14:54:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728856AbgEDOyH (ORCPT ); Mon, 4 May 2020 10:54:07 -0400 Received: from foss.arm.com ([217.140.110.172]:46662 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727106AbgEDOyH (ORCPT ); Mon, 4 May 2020 10:54:07 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2BA381FB; Mon, 4 May 2020 07:54:06 -0700 (PDT) Received: from [10.163.71.79] (unknown [10.163.71.79]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 332DE3F305; Mon, 4 May 2020 07:54:00 -0700 (PDT) Subject: Re: [PATCH] arm64/cpuinfo: Drop boot_cpu_data To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Mark Brown , Suzuki Poulose , linux-kernel@vger.kernel.org References: <1588595400-4560-1-git-send-email-anshuman.khandual@arm.com> <20200504124321.GA73375@C02TD0UTHF1T.local> From: Anshuman Khandual Message-ID: <224296d1-086a-5516-95a8-8f4ad5c533d9@arm.com> Date: Mon, 4 May 2020 20:23:08 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20200504124321.GA73375@C02TD0UTHF1T.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/04/2020 06:13 PM, Mark Rutland wrote: > On Mon, May 04, 2020 at 06:00:00PM +0530, Anshuman Khandual wrote: >> A global boot_cpu_data is not really required. Lets drop this. > > I don't think it's true that this isn't required today. > > One reason that we have both boot_cpu_data and a cpu_data variable for > CPU0 is that CPU0 itself can be hotplugged out then back in, and this > allows us to detect if CPU0's features have changed (e.g. due to FW > failing to configure it appropriately, or real physical hotplug > occurring). Understood. After hotplug, CPU0 will come back via secondary_start_kernel() where it's current register values will be checked against earlier captured values i.e boot_cpu_data. But wondering why should CPU0 be treated like any other secondary CPU. IOW in case the fresh boot CPU register values dont match with boot_cpu_data, should not the online process just be declined ? AFAICS, current approach will let the kernel run with taint in case of a mismatch. > > So NAK to the patch as it stands. If we're certain we capture all of > those details even without boot_cpu_data, then we should make other > changes to make that clear (e.g. removing it as an argument to > update_cpu_features()). There might not be another way, unless we can override CPU0's cpu_data variable when the boot CPU comes back in after vetting against existing values. Is there any particular reason to store the very first boot CPU0 info for ever ? Passing on CPU0's cpu_data variable in update_cpu_features() for secondary CPUs during boot still make sense. It helps in finalizing register values. Re-entering CPU0's test against boot_cpu_data seems different.