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=-11.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 0729FC55179 for ; Thu, 5 Nov 2020 15:28:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9F77D20735 for ; Thu, 5 Nov 2020 15:28:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="YC6IKs47" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731248AbgKEP2j (ORCPT ); Thu, 5 Nov 2020 10:28:39 -0500 Received: from linux.microsoft.com ([13.77.154.182]:50426 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731008AbgKEP2j (ORCPT ); Thu, 5 Nov 2020 10:28:39 -0500 Received: from sequoia (162-237-133-238.lightspeed.rcsntx.sbcglobal.net [162.237.133.238]) by linux.microsoft.com (Postfix) with ESMTPSA id 2FDBF20B4905; Thu, 5 Nov 2020 07:28:38 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 2FDBF20B4905 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1604590118; bh=VyQRj/mpxm9GfobHDwbYjGE7RFRkhhznZBfoocZfick=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YC6IKs47Lp3xQf7bEgV0XxMkog66q911oiThRo0AH8Y1rjkAbVBJGWYE/0SP+ErwI r5cTr3GyWm0V191s8hQyjouNQDYnCwxZa7gaGSrDgot9Z7psJxPC3VITmX7Q+dBiiy UJmyYHELYWkgjnYhZhdiZO37wr/LpOqHVKDVdGv4= Date: Thu, 5 Nov 2020 09:28:36 -0600 From: Tyler Hicks To: Will Deacon Cc: Catalin Marinas , Pavel Tatashin , Rob Herring , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/2] arm64: Implement CONFIG_CMDLINE_EXTEND Message-ID: <20201105152836.GB4472@sequoia> References: <20200921191557.350256-1-tyhicks@linux.microsoft.com> <20201103155952.GA4335@sequoia> <20201104120812.GA6632@willie-the-truck> <20201105054009.GA4472@sequoia> <20201105095853.GA7952@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201105095853.GA7952@willie-the-truck> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-11-05 09:58:54, Will Deacon wrote: > On Wed, Nov 04, 2020 at 11:40:09PM -0600, Tyler Hicks wrote: > > On 2020-11-04 12:08:12, Will Deacon wrote: > > > On Tue, Nov 03, 2020 at 09:59:52AM -0600, Tyler Hicks wrote: > > > > On 2020-09-21 14:15:55, Tyler Hicks wrote: > > > > > Provide the CONFIG_CMDLINE_EXTEND config option for arm64 kernels. This > > > > > config option can be used to extend the kernel command line parameters, > > > > > specified by the bootloader, with additional command line parameters > > > > > specified in the kernel configuration. > > > > > > > > Hi Catalin and Will - Friendly ping on this series now that we're > > > > on the other side of the 5.10 merge window. I hope it can be considered > > > > for 5.10+1. Let me know if I need to rebase/resubmit. Thanks! > > > > > > Can you use bootconfig to achieve what you need? > > > > Thanks for mentioning bootconfig. I hadn't considered it. > > > > After reading the docs and code, I see a few reasons why I can't use it > > out of the box: > > > > 1) It requires "bootconfig" to be appended to the kernel command line. > > My proposed patch series makes it possible to append new options to > > the kernel command line in situations where the bootloader is not > > interactive. This presents a circular dependency problem for my use > > case. > > > > A new config option could be added to force the enablement of > > bootconfig but that would sort of be a single-use duplicate of > > CONFIG_CMDLINE_EXTEND's functionality. > > > > 2) Not all kernel command line options can be configured using > > bootconfig. For example, the "nokaslr" and "crashkernel=" parameters > > are parsed/handled before setup_boot_config() is called. KASLR can > > be disabled via a kernel config change but there's no config option > > equivalent for "crashkernel=". Changing the "crashkernel=" command > > line option is something that I need to support because a > > development/debug kernel build often requires a larger reservation > > and we find ourselves adjusting the "crashkernel=" value fairly > > often. > > > > 3) External FIT image build systems do not yet support bootconfig since > > it is so new. It is completely fair if you file this away in your > > not-my-problem folder but simple kernel config modifications, as > > needed for CONFIG_CMDLINE_EXTEND, are something that every image > > build system is likely to support today. > > > > All that said, I do really like the look of bootconfig. Unfortunately, > > it doesn't let me achieve everything I need. > > Ok, well thanks for having a look. A follow-up question I have is how is > this handled on x86? They don't appear to have CONFIG_CMDLINE_EXTEND either > afaict. Is it because their bootloader story tends to be more uniform? x86's equivalent was implemented by commit 516cbf3730c4 ("x86, bootup: add built-in kernel command line for x86 (v2)"). To summarize, you have to enable CONFIG_CMDLINE_BOOL and then that lets you define built-in command line parameters in CONFIG_CMDLINE. However, it is backwards in that the command line provided by the bootloader is appended onto the end of CONFIG_CMDLINE. This doesn't seem as useful to me because, using the crashkernel= example from above, the bootloader provided crashkernel= value may need to be overridden by the built-in command line to provide a different crashkernel= value for the particular kernel build being booted. Most kernel command line parameter parsers are implemented in a way that supports multiple instances of the parameter while only honoring the last instance. Tyler > > Will >