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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 C12E9C388F7 for ; Tue, 3 Nov 2020 12:47:06 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 563DA20731 for ; Tue, 3 Nov 2020 12:47:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="17uWmSuN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 563DA20731 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=7Y0WfJbO9lsmJ44vW+QOLBXCsipAT142lvOdDZw/KTU=; b=17uWmSuNrSDYnkThccBOWODR9 s2VTbyNi7N4YlJoSwX+wCcmnoh3+R5KDmXXfTXuSlWQo5YsUls8Hv88AFc15EFQHtbLe34/5UboRo X1tzzKlmoEKMPNnQMSFzNEu86D6o83wKrzR36X7JxOIihCesO5Bbr/9WKETcQRnKdjRrz/hd89dX+ 10aKmc20I3jVU5pq0UGXuB+EXmhqH7UIlGgMCISBXPSVAJ0ieMI9vFc7tWcDJ38e8HuJAPYHRxk/o lZC8061J7y02oygxgLbJfZrN85d2nHopsk5E0BdfCMZpNVZX90HSnDS7J4z/+VKzHAF+hvNvnf2aM mShwHJPmA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kZvhm-0006Lk-DO; Tue, 03 Nov 2020 12:46:31 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kZvhj-0006Kg-6G for linux-arm-kernel@lists.infradead.org; Tue, 03 Nov 2020 12:46:28 +0000 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 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-Disposition: inline In-Reply-To: <20201103121721.5166-4-will@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201103_074627_387805_1E3692D8 X-CRM114-Status: GOOD ( 20.28 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kees Cook , Peter Zijlstra , Catalin Marinas , Masahiro Yamada , linux-kernel@vger.kernel.org, Sami Tolvanen , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel