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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 2AA78C282CB for ; Tue, 5 Feb 2019 08:58:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EFBA32083B for ; Tue, 5 Feb 2019 08:58:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="yS+MNRtT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728422AbfBEI6A (ORCPT ); Tue, 5 Feb 2019 03:58:00 -0500 Received: from merlin.infradead.org ([205.233.59.134]:44232 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726161AbfBEI57 (ORCPT ); Tue, 5 Feb 2019 03:57:59 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=CF/RC3W5xm7zd9ysv4e/F3pdmJtiDQPGeiw38Z70CUI=; b=yS+MNRtTSkQ3fcwutcMIpbedP hUW1JgTTe0hUUDZsfZfv4dU+9ZpURsy9GhX/hE2RWp0Nmcn6CzXEJBzmi7EU4jBQkRlF7VbgC5Lz9 KMhleFbaY5Pv6vQg9qid3ZCIYt+0812cvZcL8VORV16gAqkGsutCTLfD0DwsL0qeP+iVa+26E/Gf8 8QoJUGLrXGBUmTlo5n7EsWK2VLOm+m7Z8jKHBilcSiX1hEpbyOKXjl2TTuSV4wqIDmBVg/eAHBB93 ndLzGcHowSo0BZJXVWh450XcGuANeyaPzxAd1stL/2vV8/z/CZJ87ldujuP2FwVUXNYN49krE5vNd rpP8tCKuA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gqwYB-00028Y-Hc; Tue, 05 Feb 2019 08:57:51 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 54F122029FA06; Tue, 5 Feb 2019 09:57:50 +0100 (CET) Date: Tue, 5 Feb 2019 09:57:50 +0100 From: Peter Zijlstra To: Dave Hansen Cc: Borislav Petkov , Thomas Gleixner , Fenghua Yu , Ingo Molnar , H Peter Anvin , Ashok Raj , Michael Chan , Ravi V Shankar , Ricardo Neri , linux-kernel , x86 Subject: Re: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid Message-ID: <20190205085750.GM17528@hirez.programming.kicks-ass.net> 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=us-ascii 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_? IOW, will my laptop in 5 years > enumerate support for it? I would bloody hope so. Just for giggles, create an little program that does LOCK prefix across a line or page boundary in a while(1) loop and 'enjoy' your laptop experience. > 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? No, we very much do want to default enable this everywhere. We might want to provide some chicken bits, like a (inheritable) PRCTL or ELF flag to disable it for those broken apps. But realistically, any app that triggers this is non-portable already, most (if not all) the RISC architecture would already kill it with SIGBUS for this. We very much want the kernel _AND_ firmware to be #AC clean, always, everywhere. Heck, I'd love for #AC to be even stronger and not only trigger on cross-line.