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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 3C9B5C4727F for ; Mon, 21 Sep 2020 22:47:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1186923A77 for ; Mon, 21 Sep 2020 22:47:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728660AbgIUWrx (ORCPT ); Mon, 21 Sep 2020 18:47:53 -0400 Received: from mga09.intel.com ([134.134.136.24]:20176 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726457AbgIUWrx (ORCPT ); Mon, 21 Sep 2020 18:47:53 -0400 IronPort-SDR: 6+t3HFiFJTADTQPyi2oYCkBlRmLSAFxM4x2/geF+KrTBdmzyXMeD5fiBfFW/MSDBHrbvKGVrSl q7pAP2ubeNnw== X-IronPort-AV: E=McAfee;i="6000,8403,9751"; a="161413478" X-IronPort-AV: E=Sophos;i="5.77,288,1596524400"; d="scan'208";a="161413478" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2020 15:47:52 -0700 IronPort-SDR: gycAem7Xa6ebdzaySf5YhbAulUIpxadRgZqjyY2BtOc6mPeDk0qKrkJkSx9M/el7HVu4AykyIt /przTO84r3ag== X-IronPort-AV: E=Sophos;i="5.77,288,1596524400"; d="scan'208";a="346716477" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.212.102.78]) ([10.212.102.78]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2020 15:47:51 -0700 Subject: Re: [PATCH v12 1/8] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking To: Dave Hansen , Pavel Machek Cc: Randy Dunlap , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Peter Zijlstra , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang References: <20200918192312.25978-1-yu-cheng.yu@intel.com> <20200918192312.25978-2-yu-cheng.yu@intel.com> <20200918205933.GB4304@duo.ucw.cz> <019b5e45-b116-7f3d-f1f2-3680afbd676c@intel.com> <20200918214020.GF4304@duo.ucw.cz> From: "Yu, Yu-cheng" Message-ID: <3a0b0baf-a0f5-fd15-3af1-0059a807100b@intel.com> Date: Mon, 21 Sep 2020 15:47:50 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On 9/21/2020 3:41 PM, Dave Hansen wrote: > On 9/21/20 3:30 PM, Yu, Yu-cheng wrote: >> +config X86_INTEL_BRANCH_TRACKING_USER >> + prompt "Intel Indirect Branch Tracking for user-mode" > > Take the "Intel " and "INTEL_" out, please. It will only cause us all > pain later if some of our x86 compatriots decide to implement this. > >> If the kernel is to be used only on older systems that do not support >> IBT, and the size of the binary is important, you can save 900 KB by >> disabling this feature. >> >> Otherwise, if unsure, say Y. > > 900k seems like a *lot*. Where the heck does that come from? > > Also, comments like that don't age very well. Consider: > > Support for this feature is only known to be present on Intel > processors released in 2020 or later. This feature is also > known to increase kernel text size substantially. > > If unsure, say N. > Thanks! > The 900KB is probably wrong today in a lot of configurations, and will; > only get *more* wrong over time. > I was talking about the vmlinux file, and probably should have said bzImage size, which has 14 KB increase when CET is enabled. Yu-cheng