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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4964FC433F5 for ; Thu, 17 Feb 2022 19:29:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245192AbiBQT3e (ORCPT ); Thu, 17 Feb 2022 14:29:34 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:48380 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232139AbiBQT3c (ORCPT ); Thu, 17 Feb 2022 14:29:32 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3D3DE129BB2; Thu, 17 Feb 2022 11:29:17 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CD70A61CFC; Thu, 17 Feb 2022 19:29:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A37C5C340E8; Thu, 17 Feb 2022 19:29:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1645126156; bh=kHigbTssltdpECsVACXjUmCjoYc8nJe1TohCmnF/uDk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=O0uHw0H9e1BKIXKJ2/u7FYUc5Y24CS+0asyxuvN2f7vHivb+GQMOmznT82N8OROTl ciHE8TSSR3HCcxH1cGTveCtkMFi00xnkQIuCZGRvpvN4TDSGie2q4rtWDyUu6b8fyb CpZGKfeAyYH2IRlf3sjYb6ycq76erMuPHJklVVz4= Date: Thu, 17 Feb 2022 20:29:13 +0100 From: Greg Kroah-Hartman To: Jakob Koschel Cc: Linus Torvalds , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Thomas Gleixner , Arnd Bergman , Andy Shevchenko , Andrew Morton , Kees Cook , Mike Rapoport , "Gustavo A. R. Silva" , Brian Johannesmeyer , Cristiano Giuffrida , "Bos, H.J." Subject: Re: [RFC PATCH 01/13] list: introduce speculative safe list_for_each_entry() Message-ID: References: <20220217184829.1991035-1-jakobkoschel@gmail.com> <20220217184829.1991035-2-jakobkoschel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220217184829.1991035-2-jakobkoschel@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 17, 2022 at 07:48:17PM +0100, Jakob Koschel wrote: > list_for_each_entry() selects either the correct value (pos) or a safe > value for the additional mispredicted iteration (NULL) for the list > iterator. > list_for_each_entry() calls select_nospec(), which performs > a branch-less select. > > On x86, this select is performed via a cmov. Otherwise, it's performed > via various shift/mask/etc. operations. > > Kasper Acknowledgements: Jakob Koschel, Brian Johannesmeyer, Kaveh > Razavi, Herbert Bos, Cristiano Giuffrida from the VUSec group at VU > Amsterdam. > > Co-developed-by: Brian Johannesmeyer > Signed-off-by: Brian Johannesmeyer > Signed-off-by: Jakob Koschel > --- > arch/x86/include/asm/barrier.h | 12 ++++++++++++ > include/linux/list.h | 3 ++- > include/linux/nospec.h | 16 ++++++++++++++++ > 3 files changed, 30 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h > index 35389b2af88e..722797ad74e2 100644 > --- a/arch/x86/include/asm/barrier.h > +++ b/arch/x86/include/asm/barrier.h > @@ -48,6 +48,18 @@ static inline unsigned long array_index_mask_nospec(unsigned long index, > /* Override the default implementation from linux/nospec.h. */ > #define array_index_mask_nospec array_index_mask_nospec > > +/* Override the default implementation from linux/nospec.h. */ > +#define select_nospec(cond, exptrue, expfalse) \ > +({ \ > + typeof(exptrue) _out = (exptrue); \ > + \ > + asm volatile("test %1, %1\n\t" \ > + "cmove %2, %0" \ > + : "+r" (_out) \ > + : "r" (cond), "r" (expfalse)); \ > + _out; \ > +}) > + > /* Prevent speculative execution past this barrier. */ > #define barrier_nospec() alternative("", "lfence", X86_FEATURE_LFENCE_RDTSC) > > diff --git a/include/linux/list.h b/include/linux/list.h > index dd6c2041d09c..1a1b39fdd122 100644 > --- a/include/linux/list.h > +++ b/include/linux/list.h > @@ -636,7 +636,8 @@ static inline void list_splice_tail_init(struct list_head *list, > */ > #define list_for_each_entry(pos, head, member) \ > for (pos = list_first_entry(head, typeof(*pos), member); \ > - !list_entry_is_head(pos, head, member); \ > + ({ bool _cond = !list_entry_is_head(pos, head, member); \ > + pos = select_nospec(_cond, pos, NULL); _cond; }); \ > pos = list_next_entry(pos, member)) > You are not "introducing" a new macro for this, you are modifying the existing one such that all users of it now have the select_nospec() call in it. Is that intentional? This is going to hit a _lot_ of existing entries that probably do not need it at all. Why not just create list_for_each_entry_nospec()? thanks, greg k-h