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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 7443AC48BE6 for ; Wed, 16 Jun 2021 10:17:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 59C2C6128B for ; Wed, 16 Jun 2021 10:17:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232115AbhFPKT3 (ORCPT ); Wed, 16 Jun 2021 06:19:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52342 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231452AbhFPKT1 (ORCPT ); Wed, 16 Jun 2021 06:19:27 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0896CC061574 for ; Wed, 16 Jun 2021 03:17:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=wQe7EuPpNIEjNOyKMWIVWWnwyDkUKEff9D3B3wNK/4I=; b=RYUoVHchqZw2eca5irQjshssma u9j2VQ1iNaw4tx5lngEeFHvkBtzElTwtYS5VpEid958dE3OinqxvFaicI+hwC79VrAIKSQCLmaw76 G4EVhj5SayCCg/SUU5GoRl1LEnXXxdwe14IoU90eXf9yYTU0W3faqaSREzRhgVBGet/IPnuoycSzz g+fWQbEGv+KxnLmleMhrNIdfw5Yri1crx09c6Ea9adrxGsQNAILjQ1VYwJ9asANbxTGaAdWNMwyZm I9h/IIoVvXW2GSTT+V0qHWiwXhanntMEQ/M0S7Y+oQAwuBxqC3rxjFhYXefq7tHJfjIYhCPCHhVHs mkUbeBHg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1ltSay-007twI-UT; Wed, 16 Jun 2021 10:16:33 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id CE8CA300269; Wed, 16 Jun 2021 12:16:27 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BCA9020277F84; Wed, 16 Jun 2021 12:16:27 +0200 (CEST) Date: Wed, 16 Jun 2021 12:16:27 +0200 From: Peter Zijlstra To: Andy Lutomirski Cc: x86@kernel.org, Dave Hansen , LKML , linux-mm@kvack.org, Andrew Morton , Mathieu Desnoyers , Nicholas Piggin , Russell King , linux-arm-kernel@lists.infradead.org, Will Deacon Subject: Re: [PATCH 7/8] membarrier: Remove arm (32) support for SYNC_CORE Message-ID: References: <2142129092ff9aa00e600c42a26c4015b7f5ceec.1623813516.git.luto@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2142129092ff9aa00e600c42a26c4015b7f5ceec.1623813516.git.luto@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 15, 2021 at 08:21:12PM -0700, Andy Lutomirski wrote: > On arm32, the only way to safely flush icache from usermode is to call > cacheflush(2). This also handles any required pipeline flushes, so > membarrier's SYNC_CORE feature is useless on arm. Remove it. So SYNC_CORE is there to help an architecture that needs to do something per CPU. If I$ invalidation is broadcast and I$ invalidation also triggers the flush of any uarch caches derived from it (if there are any). Now arm_syscall() NR(cacheflush) seems to do flush_icache_user_range(), which, if I read things right, end up in arch/arm/mm/*.S, but that doesn't consider cache_ops_need_broadcast(). Will suggests that perhaps ARM 11MPCore might need this due to their I$ flush maybe not being broadcast