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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 9D531C48BE6 for ; Wed, 16 Jun 2021 11:11:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 48F126105A for ; Wed, 16 Jun 2021 11:11:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 48F126105A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D2C3C6B0070; Wed, 16 Jun 2021 07:11:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CB5586B0071; Wed, 16 Jun 2021 07:11:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B09836B0072; Wed, 16 Jun 2021 07:11:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0196.hostedemail.com [216.40.44.196]) by kanga.kvack.org (Postfix) with ESMTP id 7B9E66B0070 for ; Wed, 16 Jun 2021 07:11:44 -0400 (EDT) Received: from smtpin22.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 1FC998249980 for ; Wed, 16 Jun 2021 11:11:44 +0000 (UTC) X-FDA: 78259321728.22.3266746 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf07.hostedemail.com (Postfix) with ESMTP id 122ACA000252 for ; Wed, 16 Jun 2021 11:11:31 +0000 (UTC) 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=XyMAqdzcY6+j3KeLnrTUviBISDYWLd3gDa93b1F9u2g=; b=DsObk91CK5kGbFl/8uFi5mInm9 N59JXOouJ2WtushIn7Kdfp3ryM7nrEPpALT1JPVeLw+CMXxO0XJliHzLziX8dDDopX1L+zZspstm/ 4/uVt7lasiSvZMfKrkdkp9a9Pi5AWBWed/bQaxuoEntQ/K+e1bI5dghh6HBYcbRfzsNiE31LuNTL7 5PE9AZyR68K7Q599y7LB8pIFQLhc0MH9foE52PmbrraQqPNaG9zpxHHf569NarOMujS3Rip/dt1Dc Sm0k/nOOytOPSbZiNv5tSUAMPDJlKL/yVoKipYrU+Vci2Sf+K02zAJzEXzImtaG3bSrdA/HzaW+M7 rV2az/lA==; 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 1ltTRm-007xhs-B1; Wed, 16 Jun 2021 11:11:09 +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 BE979300252; Wed, 16 Jun 2021 13:10:58 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id ADDA420C169EB; Wed, 16 Jun 2021 13:10:58 +0200 (CEST) Date: Wed, 16 Jun 2021 13:10:58 +0200 From: Peter Zijlstra To: "Russell King (Oracle)" Cc: Andy Lutomirski , x86@kernel.org, Dave Hansen , LKML , linux-mm@kvack.org, Andrew Morton , Mathieu Desnoyers , Nicholas Piggin , 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> <20210616103446.GC22278@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210616103446.GC22278@shell.armlinux.org.uk> Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=DsObk91C; spf=none (imf07.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org; dmarc=none X-Stat-Signature: xqotwora99dipcfxejikuk9dpg46pbge X-Rspamd-Queue-Id: 122ACA000252 X-Rspamd-Server: rspam06 X-HE-Tag: 1623841891-579197 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jun 16, 2021 at 11:34:46AM +0100, Russell King (Oracle) wrote: > On Wed, Jun 16, 2021 at 12:20:06PM +0200, Peter Zijlstra wrote: > > On Wed, Jun 16, 2021 at 12:16:27PM +0200, Peter Zijlstra wrote: > > > 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). > > > > Incomplete sentence there: + then we don't need SYNC_CORE. > > > > > 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 > > If it leaves other cores with incoherent I cache, then that's already > a problem for SMP cores, since there could be no guarantee that the > modifications made by one core will be visible to some other core that > ends up running that code - and there is little option for userspace to > work around that except by pinning the thread making the modifications > and subsequently executing the code to a core. That's where SYNC_CORE can help. Or you make sys_cacheflush() do a system wide IPI. > The same is also true of flush_icache_range() - which is used when > loading a kernel module. In the case Will is referring to, these alias > to the same code. Yes, cache_ops_need_broadcast() seems to be missing in more places.