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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 A26AAC433F4 for ; Tue, 18 Sep 2018 07:37:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6429320858 for ; Tue, 18 Sep 2018 07:37:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6429320858 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729250AbeIRNJP (ORCPT ); Tue, 18 Sep 2018 09:09:15 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:40462 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727404AbeIRNJP (ORCPT ); Tue, 18 Sep 2018 09:09:15 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1E262ED1; Tue, 18 Sep 2018 00:37:54 -0700 (PDT) Received: from [10.4.13.92] (e112298-lin.Emea.Arm.com [10.4.13.92]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 32B073F5C0; Tue, 18 Sep 2018 00:37:52 -0700 (PDT) Subject: Re: [PATCH v5 03/27] arm64: alternative: Apply alternatives early in boot process To: Daniel Thompson Cc: James Morse , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, joel@joelfernandes.org, marc.zyngier@arm.com, mark.rutland@arm.com, christoffer.dall@arm.com, catalin.marinas@arm.com, will.deacon@arm.com References: <1535471497-38854-1-git-send-email-julien.thierry@arm.com> <1535471497-38854-4-git-send-email-julien.thierry@arm.com> <3becf020-b230-beb8-b304-d8097377f234@arm.com> <78781d82-e5c4-c590-6c0c-e7d2db456bf9@arm.com> <20180917234400.ctq3w2u6fi5s5coj@holly.lan> From: Julien Thierry Message-ID: <9505fbcc-796f-78bd-80b7-21d879c5e0bc@arm.com> Date: Tue, 18 Sep 2018 08:37:49 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180917234400.ctq3w2u6fi5s5coj@holly.lan> Content-Type: text/plain; charset=utf-8; format=flowed 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 18/09/18 00:44, Daniel Thompson wrote: > On Wed, Sep 12, 2018 at 05:49:09PM +0100, Julien Thierry wrote: >>>> + __apply_alternatives(®ion, false, boot_capabilities); >>>> +} >>>> + >>>> #ifdef CONFIG_MODULES >>>> void apply_alternatives_module(void *start, size_t length) >>>> { >>> >>>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >>>> index 3bc1c8b..0d1e41e 100644 >>>> --- a/arch/arm64/kernel/cpufeature.c >>>> +++ b/arch/arm64/kernel/cpufeature.c >>>> @@ -52,6 +52,8 @@ >>>> DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS); >>>> EXPORT_SYMBOL(cpu_hwcaps); >>>> +unsigned long boot_capabilities; >>>> + >>>> /* >>>> * Flag to indicate if we have computed the system wide >>>> * capabilities based on the boot time active CPUs. This >>>> @@ -1375,6 +1377,9 @@ static void __update_cpu_capabilities(const struct arm64_cpu_capabilities *caps, >>>> if (!cpus_have_cap(caps->capability) && caps->desc) >>>> pr_info("%s %s\n", info, caps->desc); >>>> cpus_set_cap(caps->capability); >>> >>> Hmm, the bitmap behind cpus_set_cap() is what cpus_have_cap() in >>> __apply_alternatives() looks at. If you had a call to __apply_alternatives after >>> update_cpu_capabilities(SCOPE_BOOT_CPU), but before any others, it would only >>> apply those alternatives... >>> >>> (I don't think there is a problem re-applying the same alternative, but I >>> haven't checked). >>> >> >> Interesting idea. If someone can confirm that patching alternatives twice is >> safe, I think it would make things simpler. > > Early versions of this patch applied the alternatives twice. I never > noticed any problems with double patching (second time round it will > write out code that is identical to what is already there so it is > merely inefficient rather than unsafe. > When you say early version, do you mean the first ones you did? Because the one I picked up (v4 I believe) had a feature mask to select which ones to apply early and then which ones to exclude when applying the rest of the features. But I admit I have not looked at the previous versions. Cheers, -- Julien Thierry