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=-8.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 67F90C49361 for ; Fri, 18 Jun 2021 00:13:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46F97613B9 for ; Fri, 18 Jun 2021 00:13:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233226AbhFRAPf (ORCPT ); Thu, 17 Jun 2021 20:15:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:35140 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233160AbhFRAPe (ORCPT ); Thu, 17 Jun 2021 20:15:34 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id C22EC613B4; Fri, 18 Jun 2021 00:13:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623975206; bh=nM5X1GSDxCk8rh3UgTy/aR3zlWC0sDSSq0YpILKyEOw=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=OMVzzQM29lbdahlsKSCVkJIHPNqJWdv46bej0dxQNvHfFZ1lx+2X51jV4n/h5APXr 6FAoQ57E0/MvTDa7+CQeg8RV0KRnQayjeq3MS/wiDkP5F/ydPJSLV1nqrNRFPJ4hYd gm2yBgu4zSYV3TAKzdCYZSBu5ih2hOszRhY5uFzyKioNIvL/5w6vnuiWSGgh7teYx5 mEqwNwWB/Vm+xbTsOZ6Yi5ETW509W13lkrpSvQyoTu8kkiZRI2S6tz0qobJj/Xvy9x 11CjCqYHnKB3Ubl663ze8hjxIMC8oG9VCEyiswd7jQh1NnrWoH4N3E2801z1EbiLK1 TzN+n0ZFCOOnw== Subject: Re: [PATCH 8/8] membarrier: Rewrite sync_core_before_usermode() and improve documentation To: Mathieu Desnoyers Cc: x86 , Dave Hansen , linux-kernel , linux-mm , Andrew Morton , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev , Nicholas Piggin , Catalin Marinas , Will Deacon , linux-arm-kernel , Peter Zijlstra , stable References: <07a8b963002cb955b7516e61bad19514a3acaa82.1623813516.git.luto@kernel.org> <1939350496.10696.1623943014767.JavaMail.zimbra@efficios.com> From: Andy Lutomirski Message-ID: <678def50-eecd-fb0f-eac0-c0ba1a442574@kernel.org> Date: Thu, 17 Jun 2021 17:13:24 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <1939350496.10696.1623943014767.JavaMail.zimbra@efficios.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/17/21 8:16 AM, Mathieu Desnoyers wrote: > ----- On Jun 15, 2021, at 11:21 PM, Andy Lutomirski luto@kernel.org wrote: > > [...] > >> +# An architecture that wants to support >> +# MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE needs to define precisely what it >> +# is supposed to do and implement membarrier_sync_core_before_usermode() to >> +# make it do that. Then it can select ARCH_HAS_MEMBARRIER_SYNC_CORE via >> +# Kconfig.Unfortunately, MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE is not a >> +# fantastic API and may not make sense on all architectures. Once an >> +# architecture meets these requirements, > > Can we please remove the editorial comment about the quality of the membarrier > sync-core's API ? Done >> +# >> +# On x86, a program can safely modify code, issue >> +# MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE, and then execute that code, via >> +# the modified address or an alias, from any thread in the calling process. >> +# >> +# On arm64, a program can modify code, flush the icache as needed, and issue >> +# MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE to force a "context synchronizing >> +# event", aka pipeline flush on all CPUs that might run the calling process. >> +# Then the program can execute the modified code as long as it is executed >> +# from an address consistent with the icache flush and the CPU's cache type. >> +# >> +# On powerpc, a program can use MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE >> +# similarly to arm64. It would be nice if the powerpc maintainers could >> +# add a more clear explanantion. > > We should document the requirements on ARMv7 as well. Done. > > Thanks, > > Mathieu >