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=-10.7 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,URIBL_BLOCKED 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 DFE9CC433ED for ; Fri, 21 May 2021 11:19:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BB821613CE for ; Fri, 21 May 2021 11:19:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234532AbhEULUc (ORCPT ); Fri, 21 May 2021 07:20:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54930 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232447AbhEULU3 (ORCPT ); Fri, 21 May 2021 07:20:29 -0400 Received: from mail-il1-x12e.google.com (mail-il1-x12e.google.com [IPv6:2607:f8b0:4864:20::12e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 36A9CC061574 for ; Fri, 21 May 2021 04:19:06 -0700 (PDT) Received: by mail-il1-x12e.google.com with SMTP id e10so16272381ilu.11 for ; Fri, 21 May 2021 04:19:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=MTX0Qm7AhkbA+fOvtExalJbmxjADAm11mbIn/fnNRss=; b=dO9akwikK1L7MlwcbXdnTRLps4QJgB1xha1wQPogUygScSXJaW5du/XlzXm1MqgnIJ 46PcP23fGM3LplYjIe7s6XbMZMdSQI6+E7YfV+PbBFA5+YU4yPfRqISwKlBas/90OXtR ei3QPH09z3illmcMTrv/HD/jbcCnyBjGUFbYs= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=MTX0Qm7AhkbA+fOvtExalJbmxjADAm11mbIn/fnNRss=; b=VyR6x6opovWDaoJHrnRVnd4ACcA09g4acEHv8pYbN/17Xg8AveidwPVkSgP9yPqroN CiwMsXBBdSJJCIwO7JcRX4+K7u/Jr1HWxPfXxK3sWV2z7tIng5lz9kylkR58nWtbQuco Hjcol80LKt9raMf7omylSM9eOl67Pkgg+A9I4KMVLIzb0VIaaplszQzi8ymWNCk2jpwb i73ZkF1VpW8SwvP1xP8Jn5JrsTBsFXj4NLbf5YHZ1fMmU8vuthLdClMzrTmrIQR0d8qE mqHM+Nr8AZHREtyo7IMqM6EBOVqXTF4jsi8xVBEu1M6O0jjEGgLihjRrZu4w2UDta/e/ 7zzg== X-Gm-Message-State: AOAM533dxVHRhXkh1dT/HaZUKk7QSpzIRbe5gVePeyrPAcymR+38TxLY q26o27A0GrSSnE76VImSeaoSCNE5dQHngRAlJBVBI/wj0fE= X-Google-Smtp-Source: ABdhPJw5ytoDllcHq6I92P84Wr865tY27OzpDBbzLRRAvV5Um8VzMHHupjvRWHZIdegH+u1OfTN4J0qXz8eb1UQbH4M= X-Received: by 2002:a05:6e02:1d82:: with SMTP id h2mr9616080ila.78.1621595945554; Fri, 21 May 2021 04:19:05 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Joel Fernandes Date: Fri, 21 May 2021 07:18:54 -0400 Message-ID: Subject: Re: config SCHED_CORE To: Peter Zijlstra Cc: Hugh Dickins , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 21, 2021 at 3:53 AM Peter Zijlstra wrote: > > On Thu, May 20, 2021 at 08:06:07PM -0700, Hugh Dickins wrote: > > Hi Peter, > > > > make oldconfig gave me no help at all on how to decide whether to choose > > SCHED_CORE Y or n, beyond it recommending Y. Maybe you'll delete that > > option later, or maybe removing the prompt string would silence it. > > Ah, you're quite right. I never seem to have gotten around to actually > writing anything useful there :/ Similarly the documentation for all > this seems to have gone missing too. > > Joel, could I ask you to refresh the document to match the current state > of things and repost? I still whole hartedly despise this RST crud, it > makes it so hard to read / modify the files. > > ( I think the latest version is here: > https://lkml.kernel.org/r/20210324214020.34142-8-joel@joelfernandes.org > ) > > Anyway, how is something like the below, Joel can add a reference to the > document once it's there. Sure thing, Peter! I will work on it and post a patch. - Joel > > --- > 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.