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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,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 8B830C43460 for ; Fri, 21 May 2021 13:37:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6ACDC610CB for ; Fri, 21 May 2021 13:37:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235861AbhEUNip (ORCPT ); Fri, 21 May 2021 09:38:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58014 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235772AbhEUNih (ORCPT ); Fri, 21 May 2021 09:38:37 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF38AC061763 for ; Fri, 21 May 2021 06:37:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=EYC/9ctrfQvAEBBAKsb7gJESMa1uCEoqi9UattPV9Xo=; b=m3FRsszyBLlzGEw05BO4uPMu9f PY8X+6lpkbRJKeAgtF6owyZ878nepODs1cMLYRRtzFmyCO1SwpTEbzutDeigngGMTyuImw1dZUsdB qzNjsA5h8kMlcLNt1AvdMB5SAFALh6rY0cIHQPE8fV56kgkQ++3iGZEJgs5fbcp4vEJjgznj9u8eU h4TeIi/aSYbyGml5bfIG27+x8IOAZf2vpjw6PHJdltTP3J0mgMe8wmC4hQVoxzVi4VpXVVZLJNk/Z D8TSse1HDs38bWF/HgVLrNVOhYoOmdYMDm2LBADXiv97xNWOtNWlx4Q3maipFI2FSPsHkaVy2cyPX yrzmvrCg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1lk5Hi-00GzXq-RY; Fri, 21 May 2021 13:34:53 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 0DE4930022A; Fri, 21 May 2021 15:33:50 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E90DB30BCEBEB; Fri, 21 May 2021 15:33:49 +0200 (CEST) Date: Fri, 21 May 2021 15:33:49 +0200 From: Peter Zijlstra To: Joel Fernandes Cc: Hugh Dickins , LKML Subject: Re: config SCHED_CORE Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 21, 2021 at 07:57:35AM -0400, Joel Fernandes wrote: > > --- > > kernel/Kconfig.preempt | 14 +++++++++++++- > > 1 file changed, 13 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt > > index ea1e3331c0ba..3c4566cd20ef 100644 > > --- a/kernel/Kconfig.preempt > > +++ b/kernel/Kconfig.preempt > > @@ -104,4 +104,16 @@ config SCHED_CORE > > bool "Core Scheduling for SMT" > > default y > > depends on SCHED_SMT > > - > > + help > > + This option enables Core scheduling, a means of coordinated task > > + selection across SMT siblings with the express purpose of creating a > > + Core wide privilidge boundary. When enabled -- see prctl(PR_SCHED_CORE) > > + -- task selection will ensure all SMT siblings will execute a task > > + from the same 'core group', forcing idle when no matching task is found. > > + > > + This provides means of mitigation against a number of SMT side-channels; > > + but is, on its own, insufficient to mitigate all known side-channels. > > + Notable: the MDS class of attacks require more. > > + > > + Default enabled for anything that has SCHED_SMT, when unused there should > > + be no impact on performance. > > This description sort of makes it sound like security is the only > usecase. Perhaps we can also add here that core-scheduling can help > performance of workloads where hyperthreading is undesired, such as > when VM providers don't want to share hyperthreads. > > Thoughts? You're right. And there's this whole class of people who want to use this to eliminate SMT interference. I'll see if I can work that in without turning the whole thing into a novella or so ;-/