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 92592C43441 for ; Thu, 22 Nov 2018 23:28:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 572CE20663 for ; Thu, 22 Nov 2018 23:28:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 572CE20663 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 S2439080AbeKWKK3 (ORCPT ); Fri, 23 Nov 2018 05:10:29 -0500 Received: from mx2.suse.de ([195.135.220.15]:57688 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2439035AbeKWKK3 (ORCPT ); Fri, 23 Nov 2018 05:10:29 -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 A92B3AEC6; Thu, 22 Nov 2018 23:28:44 +0000 (UTC) Date: Fri, 23 Nov 2018 00:28:42 +0100 (CET) From: Jiri Kosina To: Thomas Gleixner cc: Ingo Molnar , LKML , x86@kernel.org, Peter Zijlstra , Andy Lutomirski , Linus Torvalds , Tom Lendacky , 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 21/24] x86/speculation: Prepare arch_smt_update() for PRCTL mode In-Reply-To: Message-ID: References: <20181121201430.559770965@linutronix.de> <20181121201724.320605317@linutronix.de> <20181122073447.GD41788@gmail.com> 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 Fri, 23 Nov 2018, Thomas Gleixner wrote: > > So I'm wondering, shouldn't firmware_restrict_branch_speculation_start()/_end() > > also enable/disable STIBP? It already enabled/disables IBRS. > > IBRS includes STIBP. True. > We don't use IBRS in the kernel otherwise because you'd have to do more > MSR writes on the protection boundaries. Just for the record -- we do have an option for IBRS in our distro kernel on SKL+ systems. There definitely is a measurable performance impact, but the MSR writes on protection boundaries are totally cheap compared to the actual IBRS runtime operation effect. -- Jiri Kosina SUSE Labs