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=-9.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 32D04C2D0A3 for ; Tue, 3 Nov 2020 12:46:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BF49120731 for ; Tue, 3 Nov 2020 12:46:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729031AbgKCMq1 (ORCPT ); Tue, 3 Nov 2020 07:46:27 -0500 Received: from foss.arm.com ([217.140.110.172]:48334 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727328AbgKCMq1 (ORCPT ); Tue, 3 Nov 2020 07:46:27 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 81536106F; Tue, 3 Nov 2020 04:46:26 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.57.89]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BD1583F718; Tue, 3 Nov 2020 04:46:24 -0800 (PST) Date: Tue, 3 Nov 2020 12:46:22 +0000 From: Mark Rutland To: Will Deacon Cc: linux-arm-kernel@lists.infradead.org, Kees Cook , Catalin Marinas , Sami Tolvanen , Masahiro Yamada , Peter Zijlstra , linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 3/4] arm64: alternatives: Remove READ_ONCE() usage during patch operation Message-ID: <20201103124622.GC40454@C02TD0UTHF1T.local> References: <20201103121721.5166-1-will@kernel.org> <20201103121721.5166-4-will@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201103121721.5166-4-will@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 03, 2020 at 12:17:20PM +0000, Will Deacon wrote: > In preparation for patching the internals of READ_ONCE() itself, replace > its usage on the alternatives patching patch with a volatile variable > instead. > > Acked-by: Peter Zijlstra (Intel) > Signed-off-by: Will Deacon Acked-by: Mark Rutland Mark. > --- > arch/arm64/kernel/alternative.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/alternative.c b/arch/arm64/kernel/alternative.c > index 73039949b5ce..a57cffb752e8 100644 > --- a/arch/arm64/kernel/alternative.c > +++ b/arch/arm64/kernel/alternative.c > @@ -21,7 +21,8 @@ > #define ALT_ORIG_PTR(a) __ALT_PTR(a, orig_offset) > #define ALT_REPL_PTR(a) __ALT_PTR(a, alt_offset) > > -static int all_alternatives_applied; > +/* Volatile, as we may be patching the guts of READ_ONCE() */ > +static volatile int all_alternatives_applied; > > static DECLARE_BITMAP(applied_alternatives, ARM64_NCAPS); > > @@ -205,7 +206,7 @@ static int __apply_alternatives_multi_stop(void *unused) > > /* We always have a CPU 0 at this point (__init) */ > if (smp_processor_id()) { > - while (!READ_ONCE(all_alternatives_applied)) > + while (!all_alternatives_applied) > cpu_relax(); > isb(); > } else { > @@ -217,7 +218,7 @@ static int __apply_alternatives_multi_stop(void *unused) > BUG_ON(all_alternatives_applied); > __apply_alternatives(®ion, false, remaining_capabilities); > /* Barriers provided by the cache flushing */ > - WRITE_ONCE(all_alternatives_applied, 1); > + all_alternatives_applied = 1; > } > > return 0; > -- > 2.29.1.341.ge80a0c044ae-goog >