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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=unavailable 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 10EA6C43612 for ; Mon, 31 Dec 2018 16:23:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D484E21871 for ; Mon, 31 Dec 2018 16:23:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=candelatech.com header.i=@candelatech.com header.b="LxnOl42N" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727496AbeLaQXM (ORCPT ); Mon, 31 Dec 2018 11:23:12 -0500 Received: from mail2.candelatech.com ([208.74.158.173]:41044 "EHLO mail2.candelatech.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726220AbeLaQXL (ORCPT ); Mon, 31 Dec 2018 11:23:11 -0500 Received: from [192.168.1.47] (104-235-168-9.evrt.wa.frontiernet.net [104.235.168.9]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail2.candelatech.com (Postfix) with ESMTPSA id 1D93740A626; Mon, 31 Dec 2018 08:22:42 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 mail2.candelatech.com 1D93740A626 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=candelatech.com; s=default; t=1546273388; bh=NNnK+sMWElOcWI7DzR+H+uq1YtnavaNDDxCsIuiq/KE=; h=Subject:To:References:Cc:From:Date:In-Reply-To:From; b=LxnOl42NZ8RqSRBOgpnVAZR5ANuQ1XKsZBglRHWzDImhmIMjXQO1eIut1wT+QMHFJ Ul4Qhfcwp4+hZeJ9fqROGWlhUDR0sL4MbZ2OuOSKTZYEeFX1VyY+gha/xwr9ep5xxN hb25Cx2i07PQmnr/5An7EDZ3iz33sOl3MLWkkV5E= Subject: Re: [PATCH] x86/speculation: Add document to describe Spectre and its mitigations To: Tim Chen , Thomas Gleixner References: <64efec3fda40c0758601bf9b1480a35d76d3c487.1545413988.git.tim.c.chen@linux.intel.com> <1c7923ec-70aa-25d4-3de1-f1b1768bb80b@candelatech.com> Cc: Jiri Kosina , Linus Torvalds , Tom Lendacky , Ingo Molnar , Peter Zijlstra , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Andi Kleen , Dave Hansen , Asit Mallick , Arjan van de Ven , Jon Masters , Waiman Long , Greg KH , Borislav Petkov , linux-kernel@vger.kernel.org, x86@kernel.org, stable@vger.kernel.org From: Ben Greear Message-ID: <5d45f3ef-a91f-815a-f532-62e75899e697@candelatech.com> Date: Mon, 31 Dec 2018 08:22:39 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/21/2018 05:17 PM, Tim Chen wrote: > On 12/21/18 1:59 PM, Ben Greear wrote: >> On 12/21/18 9:44 AM, Tim Chen wrote: >>> Thomas, >>> >>> Andi and I have made an update to our draft of the Spectre admin guide. >>> We may be out on Christmas vacation for a while. But we want to >>> send it out for everyone to take a look. >> >> Can you add a section on how to compile out all mitigations that have anything >> beyond negligible performance impact for those running systems where performance >> is more important than security? >> > > If you don't worry about security and performance is paramount, then > boot with "nospectre_v2". That's explained in the document. There seem to be lots of different variants of this type of problem. It was not clear to me that just doing nospectre_v2 would be sufficient to get back full performance. And anyway, I would like to compile the kernel to not need that command-line option, so I am still interesting in what compile options need to be set to what values... Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com