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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E2A41C7619A for ; Wed, 5 Apr 2023 10:44:05 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 767426B0071; Wed, 5 Apr 2023 06:44:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 715AE6B0072; Wed, 5 Apr 2023 06:44:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5DD106B007E; Wed, 5 Apr 2023 06:44:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 4B6076B0071 for ; Wed, 5 Apr 2023 06:44:05 -0400 (EDT) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id CD6561C68E5 for ; Wed, 5 Apr 2023 10:44:04 +0000 (UTC) X-FDA: 80647002408.17.5FA45E9 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf26.hostedemail.com (Postfix) with ESMTP id 22F0214000C for ; Wed, 5 Apr 2023 10:44:02 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=RfEi0EWH; spf=pass (imf26.hostedemail.com: domain of frederic@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=frederic@kernel.org; dmarc=pass (policy=none) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1680691443; a=rsa-sha256; cv=none; b=JsPtwC9M4B131B2mfCPK8DuhPW40jlF15aA0xF48oYvdjGKPRban2ywqlDRTEODaetyw6l vEfF0CyicOWr6i9AhtHfCqy2GjV3Hlf8ZydrlWsWwYPRHvnUlTmRxBARCMc50ENa2g2Ktc yGoqmfJkVsE5f3hmLA0yL6g/kJ2VlQo= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=RfEi0EWH; spf=pass (imf26.hostedemail.com: domain of frederic@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=frederic@kernel.org; dmarc=pass (policy=none) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1680691443; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=FWEoECAfY+wWsgkbeCj2WH8L2epM/LlmHPmMJIPH3QM=; b=XQscZE4DbmpPyYP55ntfZDcaqbFS0CQ8grnwMxAzsY3BWPRf8GPEkWq7m4v3ZkgKd1mzcm s+V7qmnkkGd7OqRuKPCVTfBTwmm6UEZbzfHoimyQMou6bhYlZjPuxpMdkPCJaghmrpFiHN U3CqA74PjUT3ylzVjetUaRnXGTEKwgk= Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 0DD036247E; Wed, 5 Apr 2023 10:44:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BFC61C433EF; Wed, 5 Apr 2023 10:44:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1680691441; bh=+ZO/yBxfJv0GaHczUgdJTBFHBjfQ/ykADeJttq42HmQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RfEi0EWHrVtgDNTDmAkQHpOA1xGMHUdirDcpsD08NWpiRE8In3RAHPfhmz+mLo3Re keFWgaWXAHpSzJgLMWdEzHtCNaP6XaC77hbIAZwK+4PpDX/Zwb9pTItZlq4DbE4Bcj gF37NoMLKD33dyuHM4yV5O3ouVk+s6lLupFGmAHvGBDdJp1MrGsgJ5ZzVLp7GXS7g2 UIOMTpAu0+CUNt+73VKyRli+76KWSC33YcG5QeaD76fiXSWmghliODfhBl98LZE/dA PhaBHuqHXYQ037jMpcPmRNTtYCqZtKeIbh0pk5/nikjbQBZDel/38qAxiwMpnOZnDc uqZAC/jHMG+Ow== Date: Wed, 5 Apr 2023 12:43:58 +0200 From: Frederic Weisbecker To: Yair Podemsky Cc: linux@armlinux.org.uk, mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, davem@davemloft.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, will@kernel.org, aneesh.kumar@linux.ibm.com, akpm@linux-foundation.org, peterz@infradead.org, arnd@arndb.de, keescook@chromium.org, paulmck@kernel.org, jpoimboe@kernel.org, samitolvanen@google.com, ardb@kernel.org, juerg.haefliger@canonical.com, rmk+kernel@armlinux.org.uk, geert+renesas@glider.be, tony@atomide.com, linus.walleij@linaro.org, sebastian.reichel@collabora.com, nick.hawkins@hpe.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, mtosatti@redhat.com, vschneid@redhat.com, dhildenb@redhat.com, alougovs@redhat.com Subject: Re: [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode Message-ID: References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230404134224.137038-4-ypodemsk@redhat.com> X-Rspam-User: X-Rspamd-Queue-Id: 22F0214000C X-Rspamd-Server: rspam01 X-Stat-Signature: cieff3yccdebdekbubixwbmht6qbtuff X-HE-Tag: 1680691442-124282 X-HE-Meta: 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 daFc7PDJ ouQWK4G+gKSIAspkfoeo3x7xjcD1DGxqTv6OgERa3ewXjsyXu8rr1/zcNQnyuDDcPYQ1rna4P0FcUwGBXYmQ2bI5mkzz8Eino2GTFsGy+S9FfWNr5ny97+J3EB1Azf1R+pt7RtHbfh5yArIh5W8vHTyxT67XEUQtro4GMbK/Pt7xzYhsOkRUkTHUi8wz6ZLbHDKdnVarVUuctvJHvZhTApU8ZcPpv/ow6fQCs8OslFiVm/lEew6KU1BB0jYAmk2J+uQQH5vQeS8eoNeNhUQlDnLiQs/rlsRdjYNOoTbTx9Av+txBfEDKfEArRp1YdQjwFPq7gpTxgvJtqFENYVuM40ZAIfOaO4VlmTjA/0EUEhifDjxXWIzgNJadb3k7e1bsppy24+bQREGmB/wALPRCtefgNOA2ObQYwE2nJNhVAQvkWOSdRj0THw9vTtLaR0EAN3hmE 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 Tue, Apr 04, 2023 at 04:42:24PM +0300, Yair Podemsky wrote: > @@ -191,6 +192,20 @@ static void tlb_remove_table_smp_sync(void *arg) > /* Simply deliver the interrupt */ > } > > + > +#ifdef CONFIG_CONTEXT_TRACKING > +static bool cpu_in_kernel(int cpu, void *info) > +{ > + struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu); Like Peter said, an smp_mb() is required here before the read (unless there is already one between the page table modification and that ct->state read?). So that you have this pairing: WRITE page_table WRITE ct->state smp_mb() smp_mb() // implied by atomic_fetch_or READ ct->state READ page_table > + int state = atomic_read(&ct->state); > + /* will return true only for cpus in kernel space */ > + return state & CT_STATE_MASK == CONTEXT_KERNEL; > +} Also note that this doesn't stricly prevent userspace from being interrupted. You may well observe the CPU in kernel but it may receive the IPI later after switching to userspace. We could arrange for avoiding that with marking ct->state with a pending work bit to flush upon user entry/exit but that's a bit more overhead so I first need to know about your expectations here, ie: can you tolerate such an occasional interruption or not? Thanks.