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 41904C433FE for ; Wed, 5 Oct 2022 11:12:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229803AbiJELMm (ORCPT ); Wed, 5 Oct 2022 07:12:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37466 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229623AbiJELMi (ORCPT ); Wed, 5 Oct 2022 07:12:38 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 4BA8452FC6; Wed, 5 Oct 2022 04:12:37 -0700 (PDT) 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 81643106F; Wed, 5 Oct 2022 04:12:43 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.3.221]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 781673F73B; Wed, 5 Oct 2022 04:12:34 -0700 (PDT) Date: Wed, 5 Oct 2022 12:12:29 +0100 From: Mark Rutland To: "Paul E. McKenney" Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, Neeraj Upadhyay , Frederic Weisbecker , Boqun Feng , Catalin Marinas , Will Deacon , Thomas Gleixner , John Ogness , Petr Mladek , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH RFC v2 rcu 6/8] arch/arm64: Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option Message-ID: References: <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1> <20220929180731.2875722-6-paulmck@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220929180731.2875722-6-paulmck@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, On Thu, Sep 29, 2022 at 11:07:29AM -0700, Paul E. McKenney wrote: > The arm64 architecture uses either an LL/SC loop (old systems) or an LSE > stadd instruction (new systems) to implement this_cpu_add(), both of which > are NMI safe. IIUC "NMI safe" here just means atomic w.r.t. an NMI being taken and modfying the same location the atomic was targetting (i.e. just like ARCH_HAVE_NMI_SAFE_CMPXCHG, which arm64 selects today). Assuming so: Acked-by: Mark Rutland Only this patch went to LAKML, so maybe an earlier patch made that clear, but I didn't spot it. As one minor nit, it would be nice to align the naming with ARCH_HAVE_NMI_SAFE_CMPXCHG and select them next to each other in the Kconfig file is possible, but the Ack stands regardless. Thanks, Mark. > This means that the old and more-efficient srcu_read_lock() > may be used in NMI context, without the need for srcu_read_lock_nmisafe(). > Therefore, add the new Kconfig option ARCH_HAS_NMI_SAFE_THIS_CPU_OPS to > arch/arm64/Kconfig, which will cause NEED_SRCU_NMI_SAFE to be deselected, > thus preserving the current srcu_read_lock() behavior. > > Link: https://lore.kernel.org/all/20220910221947.171557773@linutronix.de/ > > Suggested-by: Neeraj Upadhyay > Suggested-by: Frederic Weisbecker > Suggested-by: Boqun Feng > Signed-off-by: Paul E. McKenney > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Thomas Gleixner > Cc: John Ogness > Cc: Petr Mladek > Cc: > --- > arch/arm64/Kconfig | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 571cc234d0b3..664725a0b5dd 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -31,6 +31,7 @@ config ARM64 > select ARCH_HAS_KCOV > select ARCH_HAS_KEEPINITRD > select ARCH_HAS_MEMBARRIER_SYNC_CORE > + select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS > select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE > select ARCH_HAS_PTE_DEVMAP > select ARCH_HAS_PTE_SPECIAL > -- > 2.31.1.189.g2e36527f23 >