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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 EFF04C282CB for ; Tue, 5 Feb 2019 06:18:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B664220821 for ; Tue, 5 Feb 2019 06:18:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="pkx4/UcY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727641AbfBEGSJ (ORCPT ); Tue, 5 Feb 2019 01:18:09 -0500 Received: from mail.skyhub.de ([5.9.137.197]:52730 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726646AbfBEGSI (ORCPT ); Tue, 5 Feb 2019 01:18:08 -0500 Received: from zn.tnic (p200300EC2BCB6B0090E35794C198FCB8.dip0.t-ipconnect.de [IPv6:2003:ec:2bcb:6b00:90e3:5794:c198:fcb8]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 099AC1EC0943; Tue, 5 Feb 2019 07:18:07 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1549347487; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=bNDAh8x4IXIDKCqNZ2W68EMbAi5ZMv/mepSYH63Qw78=; b=pkx4/UcYSIloxjEDmvbRdKjs4RJgSGlxcLA+fIiH0oRVIqXjSGE+mY2Gu8apWQu4cse5uw ccWufTTa3esRNXXFuutd2/AmuFDcdeSf3/LHkeRX1DLuphI9ZUc/z40ALmm3hhxIXMmwCs CXAbxPEzYr3BDpkF+V3IWf8nBW09pxk= Date: Tue, 5 Feb 2019 07:18:01 +0100 From: Borislav Petkov To: Dave Hansen Cc: Thomas Gleixner , Fenghua Yu , Ingo Molnar , H Peter Anvin , Ashok Raj , Peter Zijlstra , Michael Chan , Ravi V Shankar , Ricardo Neri , linux-kernel , x86 Subject: Re: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid Message-ID: <20190205061801.GC21801@zn.tnic> References: <1549084491-57808-1-git-send-email-fenghua.yu@intel.com> <1549084491-57808-9-git-send-email-fenghua.yu@intel.com> <9fa7406b-113f-fe0a-9fc7-ef00b3a6b620@intel.com> <20190204195704.GJ29639@zn.tnic> <5c2f0af3-1740-f16b-6ff6-6bec6a325034@intel.com> <20190204214044.GN29639@zn.tnic> <722af610-da30-2318-9ddd-d991238ce334@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <722af610-da30-2318-9ddd-d991238ce334@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 04, 2019 at 03:24:23PM -0800, Dave Hansen wrote: > Actually, there's one part of all this that I forgot. Will split lock > detection be enumerated _widely_? You never know what users will do. The moment it gets out, it better be designed properly, along with the chicken bits. > IOW, will my laptop in 5 years enumerate support for it? Don't tell me this is going to be another MPX fiasco :-\ Or is this something along the lines of "let's see whether it takes off and if yes, we'll commit to it or otherwise remove it and not even waste a CPUID leaf"? > If so, we surely don't want to enable this everyhwhere: it will break > old apps. Doesn't that mean that we need both feature detection and > another separate bit for folks to opt-in? Well, if it breaks old apps, it probably needs to be opt-in anyway. And for that you don't need setcpuid either - you simply boot with "split_lock_ac" or whatever and the kernel pokes that MSR_TEST_CTL or whatever else it needs to detect in hw for split lock and sets the X86_FEATURE bits if detection is successful. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.