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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 16FF1C433DF for ; Thu, 14 May 2020 11:33:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D5744206A5 for ; Thu, 14 May 2020 11:33:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726128AbgENLdT (ORCPT ); Thu, 14 May 2020 07:33:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36090 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726010AbgENLdS (ORCPT ); Thu, 14 May 2020 07:33:18 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 94955C061A0C for ; Thu, 14 May 2020 04:33:18 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jZC6o-0004st-Pi; Thu, 14 May 2020 13:33:02 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 168751004CE; Thu, 14 May 2020 13:33:02 +0200 (CEST) From: Thomas Gleixner To: "Singh\, Balbir" , "linux-kernel\@vger.kernel.org" Cc: "keescook\@chromium.org" , "thomas.lendacky\@amd.com" , "tony.luck\@intel.com" , "benh\@kernel.crashing.org" , "jpoimboe\@redhat.com" , "x86\@kernel.org" , "dave.hansen\@intel.com" Subject: Re: [PATCH v6 5/6] Optionally flush L1D on context switch In-Reply-To: References: <20200510014803.12190-1-sblbir@amazon.com> <20200510014803.12190-6-sblbir@amazon.com> <875zcz3j47.fsf@nanos.tec.linutronix.de> Date: Thu, 14 May 2020 13:33:02 +0200 Message-ID: <87pnb6zr81.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Balbir, "Singh, Balbir" writes: > On Wed, 2020-05-13 at 18:16 +0200, Thomas Gleixner wrote: >> Balbir Singh writes: >> But looking at this deeper (yes I should have noticed earlier): >> >> Why do we need yet another PRCTL? >> >> We already have PR_SET_SPECULATION_CTRL/PR_GET_SPECULATION_CTRL. That >> L1D flush thingy fits into this category, right? > > It does, I thought about it for a while when I was changing the code and > left it aside because, looking at the definition > > 1 PR_SPEC_ENABLE The speculation feature is enabled, > mitigation is disabled. > 2 PR_SPEC_DISABLE The speculation feature is disabled, > mitigation is enabled. > > With L1D flush, there is no overriding of the feature as such (as in > enable when the mitigation is disabled and vice-versa). I am happy to > reconsider my initial thought though. L1D is always enabled as L1D will be a source of trouble forever :) Thanks, tglx