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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 7DA68C47253 for ; Fri, 1 May 2020 17:45:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 60B4A2173E for ; Fri, 1 May 2020 17:45:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="dpXdnK0H" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729953AbgEARpZ (ORCPT ); Fri, 1 May 2020 13:45:25 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:37744 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729772AbgEARpZ (ORCPT ); Fri, 1 May 2020 13:45:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588355123; 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:autocrypt:autocrypt; bh=3erjJ6PUj0+kTbH6WM4sv87u+V7N5mk0eIrgDOfdhPg=; b=dpXdnK0HidpvX5Hh5H75j9sj+9JD0r3X4Dy+sP3HLxnFkA6KUCY45R+y4GD7PRrM/UKDs2 h8HLbj+tsnx6r0H4DVdD4fgRjbzB4NL6YNjbFgaHgKF5tTVcy2DNLGj18n647btc69kRQF 892wHm8FwItYC1EYgZy7+Xh14ax7CXU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-247-RMUFCZcdPIaCTt6gBqiHfA-1; Fri, 01 May 2020 13:45:19 -0400 X-MC-Unique: RMUFCZcdPIaCTt6gBqiHfA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2B00D835B8E; Fri, 1 May 2020 17:45:17 +0000 (UTC) Received: from [10.36.112.180] (ovpn-112-180.ams2.redhat.com [10.36.112.180]) by smtp.corp.redhat.com (Postfix) with ESMTP id 69C445C1D2; Fri, 1 May 2020 17:45:08 +0000 (UTC) Subject: Re: [PATCH v2 2/3] mm/memory_hotplug: Introduce MHP_NO_FIRMWARE_MEMMAP To: Dan Williams Cc: Andrew Morton , "Eric W. Biederman" , Linux Kernel Mailing List , Linux MM , virtio-dev@lists.oasis-open.org, virtualization@lists.linux-foundation.org, linuxppc-dev , Linux ACPI , linux-nvdimm , linux-hyperv@vger.kernel.org, linux-s390 , xen-devel , Michal Hocko , "Michael S . Tsirkin" , Michal Hocko , Pankaj Gupta , Wei Yang , Baoquan He References: <20200430102908.10107-1-david@redhat.com> <20200430102908.10107-3-david@redhat.com> <87pnbp2dcz.fsf@x220.int.ebiederm.org> <1b49c3be-6e2f-57cb-96f7-f66a8f8a9380@redhat.com> <871ro52ary.fsf@x220.int.ebiederm.org> <373a6898-4020-4af1-5b3d-f827d705dd77@redhat.com> <875zdg26hp.fsf@x220.int.ebiederm.org> <20200430152403.e0d6da5eb1cad06411ac6d46@linux-foundation.org> <5c908ec3-9495-531e-9291-cbab24f292d6@redhat.com> <2d019c11-a478-9d70-abd5-4fd2ebf4bc1d@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: <62dd4ce2-86cc-5b85-734f-ec8766528a1b@redhat.com> Date: Fri, 1 May 2020 19:45:08 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01.05.20 19:39, Dan Williams wrote: > On Fri, May 1, 2020 at 10:21 AM David Hildenbrand wrote: >> >> On 01.05.20 18:56, Dan Williams wrote: >>> On Fri, May 1, 2020 at 2:34 AM David Hildenbrand wrote: >>>> >>>> On 01.05.20 00:24, Andrew Morton wrote: >>>>> On Thu, 30 Apr 2020 20:43:39 +0200 David Hildenbrand wrote: >>>>> >>>>>>> >>>>>>> Why does the firmware map support hotplug entries? >>>>>> >>>>>> I assume: >>>>>> >>>>>> The firmware memmap was added primarily for x86-64 kexec (and still, is >>>>>> mostly used on x86-64 only IIRC). There, we had ACPI hotplug. When DIMMs >>>>>> get hotplugged on real HW, they get added to e820. Same applies to >>>>>> memory added via HyperV balloon (unless memory is unplugged via >>>>>> ballooning and you reboot ... the the e820 is changed as well). I assume >>>>>> we wanted to be able to reflect that, to make kexec look like a real reboot. >>>>>> >>>>>> This worked for a while. Then came dax/kmem. Now comes virtio-mem. >>>>>> >>>>>> >>>>>> But I assume only Andrew can enlighten us. >>>>>> >>>>>> @Andrew, any guidance here? Should we really add all memory to the >>>>>> firmware memmap, even if this contradicts with the existing >>>>>> documentation? (especially, if the actual firmware memmap will *not* >>>>>> contain that memory after a reboot) >>>>> >>>>> For some reason that patch is misattributed - it was authored by >>>>> Shaohui Zheng , who hasn't been heard from in >>>>> a decade. I looked through the email discussion from that time and I'm >>>>> not seeing anything useful. But I wasn't able to locate Dave Hansen's >>>>> review comments. >>>> >>>> Okay, thanks for checking. I think the documentation from 2008 is pretty >>>> clear what has to be done here. I will add some of these details to the >>>> patch description. >>>> >>>> Also, now that I know that esp. kexec-tools already don't consider >>>> dax/kmem memory properly (memory will not get dumped via kdump) and >>>> won't really suffer from a name change in /proc/iomem, I will go back to >>>> the MHP_DRIVER_MANAGED approach and >>>> 1. Don't create firmware memmap entries >>>> 2. Name the resource "System RAM (driver managed)" >>>> 3. Flag the resource via something like IORESOURCE_MEM_DRIVER_MANAGED. >>>> >>>> This way, kernel users and user space can figure out that this memory >>>> has different semantics and handle it accordingly - I think that was >>>> what Eric was asking for. >>>> >>>> Of course, open for suggestions. >>> >>> I'm still more of a fan of this being communicated by "System RAM" >> >> I was mentioning somewhere in this thread that "System RAM" inside a >> hierarchy (like dax/kmem) will already be basically ignored by >> kexec-tools. So, placing it inside a hierarchy already makes it look >> special already. >> >> But after all, as we have to change kexec-tools either way, we can >> directly go ahead and flag it properly as special (in case there will >> ever be other cases where we could no longer distinguish it). >> >>> being parented especially because that tells you something about how >>> the memory is driver-managed and which mechanism might be in play. >> >> The could be communicated to some degree via the resource hierarchy. >> >> E.g., >> >> [root@localhost ~]# cat /proc/iomem >> ... >> 140000000-33fffffff : Persistent Memory >> 140000000-1481fffff : namespace0.0 >> 150000000-33fffffff : dax0.0 >> 150000000-33fffffff : System RAM (driver managed) >> >> vs. >> >> :/# cat /proc/iomem >> [...] >> 140000000-333ffffff : virtio-mem (virtio0) >> 140000000-147ffffff : System RAM (driver managed) >> 148000000-14fffffff : System RAM (driver managed) >> 150000000-157ffffff : System RAM (driver managed) >> >> Good enough for my taste. >> >>> What about adding an optional /sys/firmware/memmap/X/parent attribute. >> >> I really don't want any firmware memmap entries for something that is >> not part of the firmware provided memmap. In addition, >> /sys/firmware/memmap/ is still a fairly x86_64 specific thing. Only mips >> and two arm configs enable it at all. >> >> So, IMHO, /sys/firmware/memmap/ is definitely not the way to go. > > I think that's a policy decision and policy decisions do not belong in > the kernel. Give the tooling the opportunity to decide whether System > RAM stays that way over a kexec. The parenthetical reference otherwise > looks out of place to me in the /proc/iomem output. What makes it > "driver managed" is how the kernel handles it, not how the kernel > names it. At least, virtio-mem is different. It really *has to be handled* by the driver. This is not a policy. It's how it works. -- Thanks, David / dhildenb