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 0147CC49EA2 for ; Fri, 18 Jun 2021 00:13:29 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A7F07613EC for ; Fri, 18 Jun 2021 00:13:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A7F07613EC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 25A106B0070; Thu, 17 Jun 2021 20:13:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 209D36B0071; Thu, 17 Jun 2021 20:13:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 083406B0072; Thu, 17 Jun 2021 20:13:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0168.hostedemail.com [216.40.44.168]) by kanga.kvack.org (Postfix) with ESMTP id C4CCD6B0070 for ; Thu, 17 Jun 2021 20:13:27 -0400 (EDT) Received: from smtpin37.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 6F47A5851 for ; Fri, 18 Jun 2021 00:13:27 +0000 (UTC) X-FDA: 78264920454.37.C86E152 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf16.hostedemail.com (Postfix) with ESMTP id 88FCA801934C for ; Fri, 18 Jun 2021 00:13:26 +0000 (UTC) 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 Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=OMVzzQM2; spf=pass (imf16.hostedemail.com: domain of luto@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=luto@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-Stat-Signature: zhydrnejb935gf47565nyk488jx9a5yj X-Rspamd-Queue-Id: 88FCA801934C X-Rspamd-Server: rspam06 X-HE-Tag: 1623975206-282898 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 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 >