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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 3CBFFC43441 for ; Sun, 18 Nov 2018 23:56:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 055E320869 for ; Sun, 18 Nov 2018 23:56:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 055E320869 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com 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 S1728149AbeKSKRz (ORCPT ); Mon, 19 Nov 2018 05:17:55 -0500 Received: from mga04.intel.com ([192.55.52.120]:11494 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726950AbeKSKRz (ORCPT ); Mon, 19 Nov 2018 05:17:55 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Nov 2018 15:56:10 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,250,1539673200"; d="scan'208";a="87445097" Received: from tassilo.jf.intel.com (HELO tassilo.localdomain) ([10.7.201.126]) by fmsmga008.fm.intel.com with ESMTP; 18 Nov 2018 15:56:10 -0800 Received: by tassilo.localdomain (Postfix, from userid 1000) id 8B799301015; Sun, 18 Nov 2018 15:56:10 -0800 (PST) From: Andi Kleen To: Linus Torvalds Cc: Jiri Kosina , Thomas Gleixner , Peter Zijlstra , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Tim Chen , Casey Schaufler , Linux List Kernel Mailing , "the arch\/x86 maintainers" , stable@vger.kernel.org Subject: Re: STIBP by default.. Revert? References: Date: Sun, 18 Nov 2018 15:56:10 -0800 In-Reply-To: (Linus Torvalds's message of "Sun, 18 Nov 2018 14:36:09 -0800") Message-ID: <871s7i0wkl.fsf@linux.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Linus Torvalds writes: > On Sun, Nov 18, 2018 at 2:17 PM Jiri Kosina wrote: >> Which gets us back to Tim's fixup patch. Do you still prefer the revert, >> given the existence of that? > > I don't think the code needs to be reverted, but the *behavior* of > just unconditionally enabling STIBP needs to be reverted. Actually I think it should be reverted. Yes of course opt-in is needed. But also when you opt-in it doesn't make sense to set STIBP when the sibling is running the same security context, which is actually a common case. So to even use it properly you would need some scheduler support to detect these cases and only enable it then with opt-in. These patches didn't even try to tackle this problem. -Andi