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 5C261C7619A for ; Wed, 5 Apr 2023 12:00:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9A5446B0071; Wed, 5 Apr 2023 08:00:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 92D7C6B0072; Wed, 5 Apr 2023 08:00:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 77FDA6B0074; Wed, 5 Apr 2023 08:00:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 5C9C56B0071 for ; Wed, 5 Apr 2023 08:00:28 -0400 (EDT) Received: from smtpin13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 486D91610FF for ; Wed, 5 Apr 2023 12:00:27 +0000 (UTC) X-FDA: 80647194894.13.EE90DD1 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf23.hostedemail.com (Postfix) with ESMTP id C0FD6140020 for ; Wed, 5 Apr 2023 12:00:24 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=g7kiVUSt; spf=pass (imf23.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1680696025; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=RSlHLlJfuqzoKBsSMqongiC+StHcDiIfT1vSmb6xVfw=; b=txHEa5K5DE+2NYvTJpEHZHBsxzB4MQr2UDsmIDcZ5hlDrEfY4TyGrFJO5HQDWAbqt6R/i4 Wk9qFIibBl0EYQzbkXaWbARmEFCDhBZnt49OCX98xIy6KxuvUnz046mKWnf/aJEycvMJmG J1rNmwLcQQzrbcj5Y+UPjgSWS36kwgM= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=g7kiVUSt; spf=pass (imf23.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1680696025; a=rsa-sha256; cv=none; b=O4vvDDkh1T3Xy0qcuVL33UliZd6PAmaUhxRZjiSE5UlfqU1MHghHE3YZ/jyxB0eyMp6jGV r/k1dcdwLMzuAG0WFieoW2P+9iP6L6xs6r1qVm4LvjOlLJDvHnwQ6ikAD/LKs2R/mZsKkC g1J5FZon0RWcVpkRoUmM/xoliGtN/aU= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1680696024; h=from:from: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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=RSlHLlJfuqzoKBsSMqongiC+StHcDiIfT1vSmb6xVfw=; b=g7kiVUStmMqlVf6kKVkdAaBI6r+wCGh1ipMKnr0c8EMjpfYZ4c2BiN7Ny8x9g4vBp3WYAM 0dfvO5luk2oRbpGJ2yGEIL0bJDqwiYRwBes6k87LtPnkdMElgeeJOKlVuRoSmmNaAeB9Vp mLOBSm9pljj1GFwaDca8gEHWvDFtCXQ= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-222-z46Q7uRrOM2UUQHFpr4zoA-1; Wed, 05 Apr 2023 08:00:22 -0400 X-MC-Unique: z46Q7uRrOM2UUQHFpr4zoA-1 Received: by mail-wm1-f72.google.com with SMTP id bi7-20020a05600c3d8700b003edecc610abso19037197wmb.7 for ; Wed, 05 Apr 2023 05:00:21 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680696020; h=content-transfer-encoding:in-reply-to:organization:from:references :cc:to:content-language:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=RSlHLlJfuqzoKBsSMqongiC+StHcDiIfT1vSmb6xVfw=; b=ZUL40fAPmX63Vk1/O89vI7DfgswlyRwwZY/0YO9kU7Tzmd89evtGAWzqMNUqeZoKIL f5oYEct2WHhzyxVeJYM4e846CiiUvbVtP/hcnc6QXk8i0Ry+ei5n5JGJ2rfjYg+0rMvE WoIj/0OO81txqaQg0xg4WdiAK6jAFC7Y0wxnccuUVDActIs1bnvEdrwPOkN6KR2xOhJ+ JgfLbxfmz+u1JIrrhIPEeQkhVDFfYfXIoU8h6RH2kwPf2REu6uYwDZxX62QG/0yWuZfz 9TR7na8gQC+Ra9rS89EYjQUNTFSK1r2X7eHMkIs9AjTxuNoZEQ2BF+BT/hd1wJ47wFgV ahhg== X-Gm-Message-State: AAQBX9fJrS3ivimsA2KGC8av180nkUq/Y4WkNEJfFKYiqqYHarV0O6xc fOznKubp1XNj9O3yfaHWsCjDoLV+g35Gi+s04SkFXaMcJl/QWt2unixnl0SQnlibVi0bfEqPL8S 0GRwRkhHWiC8= X-Received: by 2002:adf:f851:0:b0:2c6:85ef:4086 with SMTP id d17-20020adff851000000b002c685ef4086mr4082503wrq.32.1680696020606; Wed, 05 Apr 2023 05:00:20 -0700 (PDT) X-Google-Smtp-Source: AKy350a1LUfUOKuj3jMotBlpC19SVSB9cyW7enGegvzefcAmYdi8D6SEfOrURf0tsGiN5OpOE9NhWQ== X-Received: by 2002:adf:f851:0:b0:2c6:85ef:4086 with SMTP id d17-20020adff851000000b002c685ef4086mr4082439wrq.32.1680696020257; Wed, 05 Apr 2023 05:00:20 -0700 (PDT) Received: from ?IPV6:2003:cb:c703:d00:ca74:d9ea:11e0:dfb? (p200300cbc7030d00ca74d9ea11e00dfb.dip0.t-ipconnect.de. [2003:cb:c703:d00:ca74:d9ea:11e0:dfb]) by smtp.gmail.com with ESMTPSA id b13-20020adff24d000000b002c573778432sm14717731wrp.102.2023.04.05.05.00.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Apr 2023 05:00:19 -0700 (PDT) Message-ID: <480e9492-2043-4788-eaff-4995e9e3b56e@redhat.com> Date: Wed, 5 Apr 2023 14:00:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH 3/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to CPUs in kernel mode To: Peter Zijlstra , Frederic Weisbecker Cc: Yair Podemsky , 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, 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 References: <20230404134224.137038-1-ypodemsk@redhat.com> <20230404134224.137038-4-ypodemsk@redhat.com> <20230405114148.GA351571@hirez.programming.kicks-ass.net> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230405114148.GA351571@hirez.programming.kicks-ass.net> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: a9kk3i3z5zezo5yjgwni7xydxw1wguji X-Rspamd-Queue-Id: C0FD6140020 X-HE-Tag: 1680696024-494549 X-HE-Meta: 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 4qtRRy4O 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 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 05.04.23 13:41, Peter Zijlstra wrote: > On Wed, Apr 05, 2023 at 01:10:07PM +0200, Frederic Weisbecker wrote: >> On Wed, Apr 05, 2023 at 12:44:04PM +0200, Frederic Weisbecker wrote: >>> On Tue, Apr 04, 2023 at 04:42:24PM +0300, Yair Podemsky wrote: >>>> + 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? >> >> Bah, actually what can we do to prevent from that racy IPI? Not much I fear... > > Yeah, so I don't think that's actually a problem. The premise is that > *IFF* NOHZ_FULL stays in userspace, then it will never observe the IPI. > > If it violates this by doing syscalls or other kernel entries; it gets > to keep the pieces. Yair is currently on vacation, so I'm replying on his behalf. Indeed, RT userspace is supposed to not call into the kernel, that's the premise. -- Thanks, David / dhildenb