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=-7.0 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 6F306C43387 for ; Fri, 21 Dec 2018 12:18:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3E98321906 for ; Fri, 21 Dec 2018 12:18:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390142AbeLUMSo (ORCPT ); Fri, 21 Dec 2018 07:18:44 -0500 Received: from mail-pg1-f195.google.com ([209.85.215.195]:36264 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388481AbeLUMSo (ORCPT ); Fri, 21 Dec 2018 07:18:44 -0500 Received: by mail-pg1-f195.google.com with SMTP id n2so2463461pgm.3 for ; Fri, 21 Dec 2018 04:18:43 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=tYajQfXn2haHQMP9WLk4eyze4RiRp3DRQkG/GKdMfEc=; b=WNx4CCxaSrQ3CaTAiVw7r4ngfMdHi5gOs1cgiDNFVEyBv9LfF8kQmDhegixEZP0Z2V DNhrFXuw5hClERVva2oumodlUSiKYTMzP8fwjksIBU4zi5vuHt1MAn4oO4lO/kq3OYIg ucHeq/jNCgPFHFjQN0CoESCyRzMNgaRNhCTnKczgu2jdL9JcXVtwZKnpTQTMTIgJVAu6 OBkVuF5keYchBZNiA1+EK7qrHUsQpEY23SwoyJKja0G+Ps/TjPa/PuKrlKaabcgZS2xH cqCt2+p8+RPhJhOwloe6KLIPdkIZbfFrGFudPUEVp+Zuz4ht6bs10t6bk0C9Gjvcs0FT i7cw== X-Gm-Message-State: AJcUukd92FgSA/pkFW5eTRc5V1phwN53PQIzyU/b/MehzLNXZkdkhcTF Bwbi+KNiJTlM7iJDBsrTJoIBRA== X-Google-Smtp-Source: ALg8bN6+VmRsmltlkpm/nsiTMmAbysDYmnYvlwhtPCha/LmiU31/IxJb4vM1avCjLdeoQ+nBu560jA== X-Received: by 2002:a63:fb15:: with SMTP id o21mr2160784pgh.211.1545394723185; Fri, 21 Dec 2018 04:18:43 -0800 (PST) Received: from bsingh.kernel.org ([125.16.97.126]) by smtp.gmail.com with ESMTPSA id b5sm60518743pfc.150.2018.12.21.04.18.40 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 21 Dec 2018 04:18:42 -0800 (PST) Subject: Re: [PATCH v2] hpet: Fix missing '=' character in the __setup() code of hpet_mmap_enable To: Greg KH Cc: clemens@ladisch.de, arnd@arndb.de, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20181220120524.30732-1-bsingh@redhat.com> <20181220122932.GB17138@kroah.com> <20181220140951.GB8621@kroah.com> From: Buland Singh Message-ID: <04420337-0df1-73ee-69d7-aa39232f495a@redhat.com> Date: Fri, 21 Dec 2018 17:48:38 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <20181220140951.GB8621@kroah.com> 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 12/20/18 7:39 PM, Greg KH wrote: > On Thu, Dec 20, 2018 at 07:12:55PM +0530, Buland Singh wrote: >> On 12/20/18 5:59 PM, Greg KH wrote: >>> On Thu, Dec 20, 2018 at 05:35:24PM +0530, Buland Singh wrote: >>>> Commit '3d035f580699 ("drivers/char/hpet.c: allow user controlled mmap for >>>> user processes")' introduced a new kernel command line parameter hpet_mmap, >>>> that is required to expose the memory map of the HPET registers to >>>> user-space. Unfortunately the kernel command line parameter 'hpet_mmap' is >>>> broken and never takes effect due to missing '=' character in the __setup() >>>> code of hpet_mmap_enable. >>>> >>>> Before this patch: >>>> >>>> dmesg output with the kernel command line parameter hpet_mmap=1 >>>> >>>> [ 0.204152] HPET mmap disabled >>>> >>>> dmesg output with the kernel command line parameter hpet_mmap=0 >>>> >>>> [ 0.204192] HPET mmap disabled >>>> >>>> After this patch: >>>> >>>> dmesg output with the kernel command line parameter hpet_mmap=1 >>>> >>>> [ 0.203945] HPET mmap enabled >>>> >>>> dmesg output with the kernel command line parameter hpet_mmap=0 >>>> >>>> [ 0.204652] HPET mmap disabled >>>> >>>> Fixes: 3d035f580699 ("drivers/char/hpet.c: allow user controlled mmap for user processes") >>>> Signed-off-by: Buland Singh >>>> --- >>>> drivers/char/hpet.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c >>>> index 4a22b4b41aef..9bffcd37cc7b 100644 >>>> --- a/drivers/char/hpet.c >>>> +++ b/drivers/char/hpet.c >>>> @@ -377,7 +377,7 @@ static __init int hpet_mmap_enable(char *str) >>>> pr_info("HPET mmap %s\n", hpet_mmap_enabled ? "enabled" : "disabled"); >>>> return 1; >>>> } >>>> -__setup("hpet_mmap", hpet_mmap_enable); >>>> +__setup("hpet_mmap=", hpet_mmap_enable); >> >> Hello Greag, >> >>> This has _never_ worked? Since 3.13? >> >> Yes, that's true :) >> >>> Why not just remove the thing as it is obvious no one actually has ever used it. > That would make the code even simpler :) >> >> Data Plane Development Kit (DPDK)[1] provides API that requires the CONFIG_HPET_MMAP >> kernel configuration option to be enabled[2]. Some end users might want to use the >> HPET MMAP functionality within the application. > > But, obviously, they really don't need to do that from the kernel > command line as no one has ever noticed this didn't work :) > > Also, that page: > >> [2] https://doc.dpdk.org/guides-18.08/linux_gsg/enable_func.html > > Does not say to use this command line option either. So if no one has > ever used it, please, let us just delete it. > > thanks, > > greg k-h > Hello Greg, It is better to allow a user to 'enable/disable' the HPET mmap from the kernel command line as per the requirement rather than recompiling the kernel to 'enable/disable' this functionality. Also as per the description in the initial patch (commit 3d035f58), the 'CONFIG_HPET_MMAP' Kconfig option has a security risk involved. Hence, keeping the CONFIG_HPET_MMAP_DEFAULT (disabled) and allowing a user to alter the default behavior using the kernel command line parameter hpet_mmap is a better solution. Regards, Buland Singh