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=-1.0 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS 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 EA66FC43441 for ; Mon, 19 Nov 2018 20:55:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B6B2D2086A for ; Mon, 19 Nov 2018 20:55:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B6B2D2086A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730924AbeKTHVB (ORCPT ); Tue, 20 Nov 2018 02:21:01 -0500 Received: from mx2.suse.de ([195.135.220.15]:52004 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730771AbeKTHUz (ORCPT ); Tue, 20 Nov 2018 02:20:55 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 3857BAD24; Mon, 19 Nov 2018 20:55:29 +0000 (UTC) Date: Mon, 19 Nov 2018 21:55:27 +0100 (CET) From: Jiri Kosina To: Thomas Gleixner cc: Tim Chen , Tom Lendacky , Ingo Molnar , Peter Zijlstra , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Andi Kleen , Dave Hansen , Casey Schaufler , Asit Mallick , Arjan van de Ven , Jon Masters , Waiman Long , linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app protection modes In-Reply-To: Message-ID: References: User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 19 Nov 2018, Thomas Gleixner wrote: > > @@ -452,12 +542,6 @@ static void __init spectre_v2_select_mitigation(void) > > setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW); > > pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n"); > > > > - /* Initialize Indirect Branch Prediction Barrier if supported */ > > - if (boot_cpu_has(X86_FEATURE_IBPB)) { > > - setup_force_cpu_cap(X86_FEATURE_USE_IBPB); > > - pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n"); > > - } > > - > > /* > > * Retpoline means the kernel is safe because it has no indirect > > * branches. Enhanced IBRS protects firmware too, so, enable restricted > > @@ -474,6 +558,43 @@ static void __init spectre_v2_select_mitigation(void) > > pr_info("Enabling Restricted Speculation for firmware calls\n"); > > } > > > > + app2app_mode = SPECTRE_V2_APP2APP_NONE; > > + if (!boot_cpu_has(X86_FEATURE_IBPB) || > > + !boot_cpu_has(X86_FEATURE_STIBP)) > > + goto set_app2app_mode; > > So before that change IBPB was usable without STIBP, now not longer. What's > the rationale? > > This patch changes a gazillion things at once and is completely > unreviewable. The patchset actually ties together IBPB and STIBP pretty closely, which is IMO a good thing; there is no good reason why anone would want just one of those (or each in a different mode), at least before this magical coscheduling exists. But I guess this fact should be documented somewhere. -- Jiri Kosina SUSE Labs