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=HEADER_FROM_DIFFERENT_DOMAINS, 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 E78D3C43441 for ; Thu, 22 Nov 2018 09:07:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B4D3C20663 for ; Thu, 22 Nov 2018 09:07:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B4D3C20663 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de 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 S2393411AbeKVTqQ (ORCPT ); Thu, 22 Nov 2018 14:46:16 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:46763 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730412AbeKVTqP (ORCPT ); Thu, 22 Nov 2018 14:46:15 -0500 Received: from hsi-kbw-5-158-153-52.hsi19.kabel-badenwuerttemberg.de ([5.158.153.52] 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 1gPkxR-00019k-VJ; Thu, 22 Nov 2018 10:07:34 +0100 Date: Thu, 22 Nov 2018 10:07:33 +0100 (CET) From: Thomas Gleixner To: Borislav Petkov cc: Tom Lendacky , LKML , x86@kernel.org, Peter Zijlstra , Andy Lutomirski , Linus Torvalds , Jiri Kosina , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Andi Kleen , Dave Hansen , Casey Schaufler , Asit Mallick , Arjan van de Ven , Jon Masters , Waiman Long , Greg KH , Dave Stewart , Kees Cook Subject: Re: [patch 15/24] x86/speculation: Add command line control for indirect branch speculation In-Reply-To: Message-ID: References: <20181121201430.559770965@linutronix.de> <20181121201723.764150349@linutronix.de> <20181121234312.GI27559@zn.tnic> User-Agent: Alpine 2.21 (DEB 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 Thu, 22 Nov 2018, Thomas Gleixner wrote: > On Thu, 22 Nov 2018, Borislav Petkov wrote: > > > + > > > + /* Initialize Indirect Branch Prediction Barrier */ > > > + 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"); > > > + } > > > > So AFAICT, if coming in here with AUTO, we won't enable IBPB and I > > *think* AMD wants IBPB enabled. At least the whitepaper says: > > > > "IBPB combined with Reptoline software support is the AMD recommended > > setting for Linux mitigation of Google Project Zero Variant 2 > > (Spectre)." > > Ok. That's indeed a step backwards, because we don't do IBPB in KVM > anymore. I'll fix that tomorrow morning when brain is more awake. OTOH, off means that all of it is disabled. Which was the case already before this when spectre_v2=off is on the command line. Now with the default to prctl/seccomp the IBPB in KVM is enabled. So no change there. > IBPB on context switch is controlled separately anyway now, so that's a > nobrainer to sort out. > > Though I wait for Toms answer whether we really want IBPB on context switch > for AMD by default. That still stands. But if we want to do that, then we need to optimize it a bit. Isn't that hard, but ... Thanks, tglx