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[209.132.180.67]) by mx.google.com with ESMTP id o123si7219289pfb.313.2018.01.18.09.14.23; Thu, 18 Jan 2018 09:14:37 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755193AbeARRMt (ORCPT + 99 others); Thu, 18 Jan 2018 12:12:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40376 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754947AbeARRMs (ORCPT ); Thu, 18 Jan 2018 12:12:48 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6967E62644; Thu, 18 Jan 2018 17:12:48 +0000 (UTC) Received: from [10.36.117.99] (ovpn-117-99.ams2.redhat.com [10.36.117.99]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9279E5D75E; Thu, 18 Jan 2018 17:12:38 +0000 (UTC) Subject: Re: [PATCH 23/35] x86/speculation: Add basic speculation control code To: Dave Hansen , Josh Poimboeuf , Peter Zijlstra Cc: David Woodhouse , Thomas Gleixner , linux-kernel@vger.kernel.org, Ashok Raj , Tim Chen , Andy Lutomirski , Linus Torvalds , Greg KH , Andrea Arcangeli , Andi Kleen , Arjan Van De Ven , Dan Williams , Jun Nakajima , Asit Mallick , Jason Baron References: <20180118134800.711245485@infradead.org> <20180118140152.830682032@infradead.org> <20180118163745.t5nmwdr53wjsl7o5@treble> <73a5735a-6a5b-0e0f-1f0b-e7cd955880d2@intel.com> From: Paolo Bonzini Message-ID: Date: Thu, 18 Jan 2018 18:12:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <73a5735a-6a5b-0e0f-1f0b-e7cd955880d2@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 18 Jan 2018 17:12:48 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18/01/2018 18:08, Dave Hansen wrote: > On 01/18/2018 08:37 AM, Josh Poimboeuf wrote: >>> >>> --- a/Documentation/admin-guide/kernel-parameters.txt >>> +++ b/Documentation/admin-guide/kernel-parameters.txt >>> @@ -3932,6 +3932,7 @@ >>> retpoline - replace indirect branches >>> retpoline,generic - google's original retpoline >>> retpoline,amd - AMD-specific minimal thunk >>> + ibrs - Intel: Indirect Branch Restricted Speculation >> Are there plans to add spectre_v2=ibrs_always to prevent SMT-based >> attacks? > > What does "ibrs_always" mean to you? > > There is a second bit in the MSR (STIBP) that is intended to keep > hyperthreads from influencing each-other. That is behavior is implicit > when IBRS is enabled. Yeah, I think we should have a mode to always leave that enabled, or always set IBRS=1. > I think ibrs_always *should* probably be kept to refer to the future > CPUs that can safely leave IBRS enabled all the time. Is that "safely" or "without throwing performance down the drain"? Does "always IBRS=1" *hinder* the mitigation on existing processor, as long as you reset IBRS=1 on kernel entry and vmexit? Or is it just slow? Paolo