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 40C8CC77B73 for ; Tue, 2 May 2023 15:45:49 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CA1916B0071; Tue, 2 May 2023 11:45:48 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C51E36B0074; Tue, 2 May 2023 11:45:48 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B1A046B0075; Tue, 2 May 2023 11:45:48 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by kanga.kvack.org (Postfix) with ESMTP id 9528B6B0071 for ; Tue, 2 May 2023 11:45:48 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1683042348; 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=/jXCvdd7DNygReOZu9LsiaslZNiW9u3JpZSmEUHzOZk=; b=J52hfGUo/TRYJPoJDNQtuEKvLYE6iLuJrW0dVqEiIgZPXDlOXQDw8GiEiDhlxZXJsWJrO5 BaBhhGk/vuMLb2TuKJNtUmTESX4zQTkfmz/2SR+Sl87n7KchJbON+w1/+5+zl606E4tptn 0MV8y6IWrKb3dYhtoRq0Xq5uKM+PBHo= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-380-Rj-tQJlSODqNAzpClLlcEw-1; Tue, 02 May 2023 11:45:45 -0400 X-MC-Unique: Rj-tQJlSODqNAzpClLlcEw-1 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-3f19517536eso13162695e9.2 for ; Tue, 02 May 2023 08:45:44 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1683042344; x=1685634344; h=content-transfer-encoding:in-reply-to:subject:organization:from :references:cc:to:content-language:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=/jXCvdd7DNygReOZu9LsiaslZNiW9u3JpZSmEUHzOZk=; b=JTJ7ZDrY5/KhJY1O97XFTVSZu/zXQQ+AI9iOOQtKxr5sdY7z3dRbLuq4SIlSdSD9Re Xi/ZWss2WOwjTGLJW487axi4KoA6mn+03blTATZK5sBc0CKgShAyCfhghqah59etegeu Wih3xbxb9Zen4jjj6MDEK3wEf8dLuxMP0PbuBZQFsObm3DX+HFm260cgk36SMp8/acBF y/6c3dwIaVmLKB4XuCxbM23Ox/FaG1kxf7ee3KnC/xytmzuRQjaw5qKy+NSVjxdVC6Vg r346XHfiskfq5eFBRM/zjStWnO88ZlY+5zpWIQUpvdD7qdYnnGbByZGSmcaABxh+i20G eMsA== X-Gm-Message-State: AC+VfDx8cZR6gLJslT16j+Rj3mPtcAIrNjs80iWZvApvrB23uJYS8pro mnJeX/YAMmgl3OK2G7R0HnwvLghCbq0Zg/y2n+mlHOQx2AySSbmZn4bET7kt13gRiDdeFwjdfhj n4+ogfGjeSow= X-Received: by 2002:a7b:c3c4:0:b0:3f3:3a81:32b with SMTP id t4-20020a7bc3c4000000b003f33a81032bmr5684972wmj.15.1683042343901; Tue, 02 May 2023 08:45:43 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ6iCnNxLty4fpwGjWmlTk0Cw9dYjc5Qp9Xj7jiPRTTMbQu6pqQFr0IF1EjCkXU8IZxvcKndbQ== X-Received: by 2002:a7b:c3c4:0:b0:3f3:3a81:32b with SMTP id t4-20020a7bc3c4000000b003f33a81032bmr5684921wmj.15.1683042343556; Tue, 02 May 2023 08:45:43 -0700 (PDT) Received: from ?IPV6:2003:cb:c700:2400:6b79:2aa:9602:7016? (p200300cbc70024006b7902aa96027016.dip0.t-ipconnect.de. [2003:cb:c700:2400:6b79:2aa:9602:7016]) by smtp.gmail.com with ESMTPSA id f25-20020a7bc8d9000000b003f0b1b8cd9bsm35846962wml.4.2023.05.02.08.45.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 May 2023 08:45:42 -0700 (PDT) Message-ID: <4fd5f74f-3739-f469-fd8a-ad0ea22ec966@redhat.com> Date: Tue, 2 May 2023 17:45:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 To: Jason Gunthorpe , Peter Xu Cc: Matthew Rosato , Christian Borntraeger , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jens Axboe , Matthew Wilcox , Dennis Dalessandro , Leon Romanovsky , Christian Benvenuti , Nelson Escobar , Bernard Metzler , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Bjorn Topel , Magnus Karlsson , Maciej Fijalkowski , Jonathan Lemon , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Christian Brauner , Richard Cochran , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, Oleg Nesterov , John Hubbard , Jan Kara , "Kirill A . Shutemov" , Pavel Begunkov , Mika Penttila , Dave Chinner , Theodore Ts'o References: <1ffbbfb7-6bca-0ab0-1a96-9ca81d5fa373@redhat.com> <3c17e07a-a7f9-18fc-fa99-fa55a5920803@linux.ibm.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings In-Reply-To: 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-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 02.05.23 17:36, Jason Gunthorpe wrote: > On Tue, May 02, 2023 at 11:32:57AM -0400, Peter Xu wrote: >>> How does s390 avoid mmu notifiers without having lots of problems?? It >>> is not really optional to hook the invalidations if you need to build >>> a shadow page table.. >> >> Totally no idea on s390 details, but.. per my read above, if the firmware >> needs to make sure the page is always available (so no way to fault it in >> on demand), which means a longterm pinning seems appropriate here. >> >> Then if pinned a must, there's no need for mmu notifiers (as the page will >> simply not be invalidated anyway)? > > And what if someone deliberately changes the mapping? memory hotplug > in the VM, or whatever? Besides s390 not supporting memory hotplug in VMs (yet): if the guest wants a different guest physical address, I guess that's the problem of the guest, and it can update it: KVM_S390_ZPCIOP_REG_AEN is triggered from QEMU via s390_pci_kvm_aif_enable(), triggered by the guest via a special instruction. If the hypervisor changes the mapping, it's just the same thing as mixing e.g. MADV_DONTNEED with longterm pinning in vfio: don't do it. And if you do it, you get to keep the mess you created for your VM. Linux will make sure to not change the mapping: for example, page migration of a pinned page will fail. But maybe I am missing something important here. -- Thanks, David / dhildenb