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=-11.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A84F5C433DF for ; Wed, 19 Aug 2020 00:58:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7C1D920657 for ; Wed, 19 Aug 2020 00:58:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726862AbgHSA6a (ORCPT ); Tue, 18 Aug 2020 20:58:30 -0400 Received: from mga09.intel.com ([134.134.136.24]:24920 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725554AbgHSA63 (ORCPT ); Tue, 18 Aug 2020 20:58:29 -0400 IronPort-SDR: zL93azRjQxXWuHMBXudIO16Tgu6ukyIDDoTT53Y6BEtcwagTA/dKwfPeFqPC2h0qeGLitp//mg qCAfQub8XRXA== X-IronPort-AV: E=McAfee;i="6000,8403,9717"; a="156100347" X-IronPort-AV: E=Sophos;i="5.76,329,1592895600"; d="scan'208";a="156100347" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Aug 2020 17:58:28 -0700 IronPort-SDR: wlO/uBnVpHem/P2UcCaELNv/WywFQxBYmZh7Hi8juyQVPQKnNcOUubfirWTqWZWpNXyW6Vbzv9 /SqTKGvo7F2w== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.76,329,1592895600"; d="scan'208";a="320290486" Received: from ranerica-svr.sc.intel.com ([172.25.110.23]) by fmsmga004.fm.intel.com with ESMTP; 18 Aug 2020 17:58:28 -0700 Date: Tue, 18 Aug 2020 18:00:19 -0700 From: Ricardo Neri To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Andy Lutomirski , Borislav Petkov , Tony Luck , x86 Subject: Re: [PATCH] x86/cpu: Fix typos and improve the comments in sync_core() Message-ID: <20200819010019.GA7074@ranerica-svr.sc.intel.com> References: <20200807032833.17484-1-ricardo.neri-calderon@linux.intel.com> <159767927411.3192.1923111080573965673.tip-bot2@tip-bot2> <20200818053130.GA3161093@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200818053130.GA3161093@gmail.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 18, 2020 at 07:31:30AM +0200, Ingo Molnar wrote: > > * tip-bot2 for Ricardo Neri wrote: > > > --- a/arch/x86/include/asm/sync_core.h > > +++ b/arch/x86/include/asm/sync_core.h > > @@ -5,6 +5,7 @@ > > #include > > #include > > #include > > +#include > > > > #ifdef CONFIG_X86_32 > > static inline void iret_to_self(void) > > @@ -54,14 +55,23 @@ static inline void iret_to_self(void) > > static inline void sync_core(void) > > { > > /* > > + * The SERIALIZE instruction is the most straightforward way to > > + * do this but it not universally available. > > + */ > > + if (static_cpu_has(X86_FEATURE_SERIALIZE)) { > > + serialize(); > > + return; > > + } > > + > > + /* > > + * For all other processors, there are quite a few ways to do this. > > + * IRET-to-self is nice because it works on every CPU, at any CPL > > + * (so it's compatible with paravirtualization), and it never exits > > + * to a hypervisor. The only down sides are that it's a bit slow > > + * (it seems to be a bit more than 2x slower than the fastest > > + * options) and that it unmasks NMIs. The "push %cs" is needed > > + * because, in paravirtual environments, __KERNEL_CS may not be a > > + * valid CS value when we do IRET directly. > > So there's two typos in the new comments, there are at least two > misapplied commas, it departs from existing style, and there's a typo > in the existing comments as well. > > Also, before this patch the 'compiler barrier' comment was valid for > the whole function (there was no branching), but after this patch it > reads of it was only valid for the legacy IRET-to-self branch. > > Which together broke my detector and triggered a bit of compulsive > bike-shed painting. ;-) See the resulting patch below. > > Thanks, > > Ingo > > ================> > From: Ingo Molnar > Date: Tue, 18 Aug 2020 07:24:05 +0200 > Subject: [PATCH] x86/cpu: Fix typos and improve the comments in sync_core() > > - Fix typos. > > - Move the compiler barrier comment to the top, because it's valid for the > whole function, not just the legacy branch. > > Signed-off-by: Ingo Molnar > --- > arch/x86/include/asm/sync_core.h | 16 ++++++++-------- > 1 file changed, 8 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/include/asm/sync_core.h b/arch/x86/include/asm/sync_core.h > index 4631c0f969d4..0fd4a9dfb29c 100644 > --- a/arch/x86/include/asm/sync_core.h > +++ b/arch/x86/include/asm/sync_core.h > @@ -47,16 +47,19 @@ static inline void iret_to_self(void) > * > * b) Text was modified on a different CPU, may subsequently be > * executed on this CPU, and you want to make sure the new version > - * gets executed. This generally means you're calling this in a IPI. > + * gets executed. This generally means you're calling this in an IPI. > * > * If you're calling this for a different reason, you're probably doing > * it wrong. > + * > + * Like all of Linux's memory ordering operations, this is a > + * compiler barrier as well. > */ > static inline void sync_core(void) > { > /* > * The SERIALIZE instruction is the most straightforward way to > - * do this but it not universally available. > + * do this, but it is not universally available. Indeed, I missed this grammar error. > */ > if (static_cpu_has(X86_FEATURE_SERIALIZE)) { > serialize(); > @@ -67,10 +70,10 @@ static inline void sync_core(void) > * For all other processors, there are quite a few ways to do this. > * IRET-to-self is nice because it works on every CPU, at any CPL > * (so it's compatible with paravirtualization), and it never exits > - * to a hypervisor. The only down sides are that it's a bit slow > + * to a hypervisor. The only downsides are that it's a bit slow > * (it seems to be a bit more than 2x slower than the fastest > - * options) and that it unmasks NMIs. The "push %cs" is needed > - * because, in paravirtual environments, __KERNEL_CS may not be a > + * options) and that it unmasks NMIs. The "push %cs" is needed, > + * because in paravirtual environments __KERNEL_CS may not be a I didn't realize that the double spaces after the period were part of the style. FWIW, Reviewed-by: Ricardo Neri