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=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 37856C43612 for ; Sun, 6 Jan 2019 14:09:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0C9452085A for ; Sun, 6 Jan 2019 14:09:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726430AbfAFOJg (ORCPT ); Sun, 6 Jan 2019 09:09:36 -0500 Received: from mail-pg1-f193.google.com ([209.85.215.193]:44618 "EHLO mail-pg1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726399AbfAFOJf (ORCPT ); Sun, 6 Jan 2019 09:09:35 -0500 Received: by mail-pg1-f193.google.com with SMTP id t13so19533164pgr.11 for ; Sun, 06 Jan 2019 06:09:35 -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=rgd6dB84Md44yvPvtVZ2yuH/V3ZSZBiAqn99ljefJz4=; b=hG0/IQvStOFv36UueMd2PcxleLNRcEwkttzmFMZD4n7G4Fjgf42qxFOAqu3HKeN9Wu XzEl0KcsvLzFBNdOOZOPwmXoLzDygMOb2zVdu+y35eA3eMtlHEKhNnCziw7fEodiL1Ss O+HCWVUoYEAg/UWtAs3xAjd+hbqI+BYiJ0H4AU0UA3xqh4ss/PsUo2oRRUNJIUgglx8y XEojAQF0AWd92vZvd3+1AiEGzrRXKi4VdNnRNdBt3GK8JRYUDTa38gzr+VM8hBZzVoKu oXib13GzzJu3IMlEyomXs2+3qH3HNYikiClT/n4G0VF1+X+jvEzOnOWO5MJiiN1mqclX o4Lg== X-Gm-Message-State: AJcUukfisZXDdtu2cBOb5pY3KX1hvsxT83JqyacBnBPzDJw+0+0UawO1 NPG0M4scxTGp1fBAIYpQs2wUMQ== X-Google-Smtp-Source: ALg8bN5ThljOhw8ZKeWDldbv/jHxdle6qABB21gIye9ibmfGRyl8Ttta1SfFbm8zCiQmoD8fNBMPxw== X-Received: by 2002:a63:85c6:: with SMTP id u189mr7550036pgd.156.1546783774636; Sun, 06 Jan 2019 06:09:34 -0800 (PST) Received: from bsingh.kernel.org ([125.16.97.119]) by smtp.gmail.com with ESMTPSA id o7sm86105875pfb.34.2019.01.06.06.09.31 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 06 Jan 2019 06:09:33 -0800 (PST) Subject: Re: [PATCH v2] hpet: Fix missing '=' character in the __setup() code of hpet_mmap_enable To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg KH , clemens@ladisch.de, arnd@arndb.de, prarit@redhat.com References: <20181220120524.30732-1-bsingh@redhat.com> <20181220122932.GB17138@kroah.com> <20181220140951.GB8621@kroah.com> <04420337-0df1-73ee-69d7-aa39232f495a@redhat.com> <20181221124603.GA7723@kroah.com> From: Buland Singh Message-ID: <7ee186c2-dba9-983c-89d1-4c7e66a6f7fb@redhat.com> Date: Sun, 6 Jan 2019 19:39:29 +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: <20181221124603.GA7723@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 12/21/18 6:16 PM, Greg KH wrote: > On Fri, Dec 21, 2018 at 05:48:38PM +0530, Buland Singh wrote: >> 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. > > It might be "nice" but given that no one has noticed that this has never > worked, for all of the years that this has been present, that means to > me that no one has ever tried it because they really do not "need" it. > >> 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. > > Again, because no one has ever noticed that this was not working, why > not just rip it out until someone speaks up as to why they have to have > this feature and the other alternatives do not work for them? > > thanks, > > greg k-h > Hello, Adding Prarit to cc list for his opinion. Regards, -- Buland Singh