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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2D3C3C433FE for ; Fri, 4 Mar 2022 17:11:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240908AbiCDRMf (ORCPT ); Fri, 4 Mar 2022 12:12:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42328 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237000AbiCDRMd (ORCPT ); Fri, 4 Mar 2022 12:12:33 -0500 X-Greylist: delayed 358 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Fri, 04 Mar 2022 09:11:45 PST Received: from angie.orcam.me.uk (angie.orcam.me.uk [78.133.224.34]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C64A71CD9EF; Fri, 4 Mar 2022 09:11:45 -0800 (PST) Received: by angie.orcam.me.uk (Postfix, from userid 500) id F09E792009D; Fri, 4 Mar 2022 18:11:44 +0100 (CET) Received: from localhost (localhost [127.0.0.1]) by angie.orcam.me.uk (Postfix) with ESMTP id EA18792009B; Fri, 4 Mar 2022 17:11:44 +0000 (GMT) Date: Fri, 4 Mar 2022 17:11:44 +0000 (GMT) From: "Maciej W. Rozycki" To: Thomas Bogendoerfer cc: Tiezhu Yang , Mike Rapoport , Andrew Morton , Xuefeng Li , linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 1/4] MIPS: Refactor early_parse_mem() to fix mem= parameter In-Reply-To: <20220304153517.GA28487@alpha.franken.de> Message-ID: References: <1646108941-27919-1-git-send-email-yangtiezhu@loongson.cn> <1646108941-27919-2-git-send-email-yangtiezhu@loongson.cn> <20220304151052.GA27642@alpha.franken.de> <20220304153517.GA28487@alpha.franken.de> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 4 Mar 2022, Thomas Bogendoerfer wrote: > > > With this patch, when add "mem=3G" to the command-line, the > > > kernel boots successfully, we can see the following messages: > > > > unfortunately this patch would break platforms without memory detection, > > which simply use mem=32M for memory configuration. Not sure how many > > rely on this mechanism. If we can make sure nobody uses it, I'm fine > > with your patch. > > maybe we could add a CONFIG option, which will be selected by > platforms, which don't need/want this usermem thing. FWIW I don't understand what the issue is here beyond that we have a bug that causes a system to hang when "mem=3G" is passed on the kernel command line. That is assuming that system does have contiguous RAM available for the kernel to use from address 0 up to 3GiB; otherwise it's a user error to tell the kernel it has that memory available (I did get bitten by that myself too): garbage in, garbage out. I think having a CONFIG option automatically selected to disable the ability to give a memory map override would handicap people in debugging their systems or working around firmware bugs, so I would rather be against it. Maciej