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 AE51FC47255 for ; Thu, 30 Apr 2020 16:49:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 82CD92070B for ; Thu, 30 Apr 2020 16:49:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NtQGQgg0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726849AbgD3Qt5 (ORCPT ); Thu, 30 Apr 2020 12:49:57 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:21431 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726565AbgD3Qtz (ORCPT ); Thu, 30 Apr 2020 12:49:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588265393; 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=B9luQcDf1oWYK0AhgcBL9GSRdmBN4OPZecF4rGENsoA=; b=NtQGQgg06wZHi/izsHAXTPyB4kDYQxjzKf5OLw+OcEIlKUNvp/GGviliu6tR9TUJPGNE1W 8GPEoQGYYhVloiPqnQG7SIU4nd5zaHdFDVKy66ku+g2G850dkAwgU3hBHrto/elCNG0i5P WSJwrRQFU3tEhkABjBuV3XTN3DM77Ak= 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-317-v8jSMvXVN_mxbmwJaY0ocA-1; Thu, 30 Apr 2020 12:49:49 -0400 X-MC-Unique: v8jSMvXVN_mxbmwJaY0ocA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 93C0F462; Thu, 30 Apr 2020 16:49:46 +0000 (UTC) Received: from [10.36.113.172] (ovpn-113-172.ams2.redhat.com [10.36.113.172]) by smtp.corp.redhat.com (Postfix) with ESMTP id 929D0512E4; Thu, 30 Apr 2020 16:49:40 +0000 (UTC) Subject: Re: [PATCH v2 2/3] mm/memory_hotplug: Introduce MHP_NO_FIRMWARE_MEMMAP To: "Eric W. Biederman" Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtio-dev@lists.oasis-open.org, virtualization@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, linux-acpi@vger.kernel.org, linux-nvdimm@lists.01.org, linux-hyperv@vger.kernel.org, linux-s390@vger.kernel.org, xen-devel@lists.xenproject.org, Michal Hocko , Andrew Morton , "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> 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: <373a6898-4020-4af1-5b3d-f827d705dd77@redhat.com> Date: Thu, 30 Apr 2020 18:49:39 +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: <871ro52ary.fsf@x220.int.ebiederm.org> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30.04.20 18:33, Eric W. Biederman wrote: > David Hildenbrand writes: >=20 >> On 30.04.20 17:38, Eric W. Biederman wrote: >>> David Hildenbrand writes: >>> >>>> Some devices/drivers that add memory via add_memory() and friends (e= .g., >>>> dax/kmem, but also virtio-mem in the future) don't want to create en= tries >>>> in /sys/firmware/memmap/ - primarily to hinder kexec from adding thi= s >>>> memory to the boot memmap of the kexec kernel. >>>> >>>> In fact, such memory is never exposed via the firmware memmap as Sys= tem >>>> RAM (e.g., e820), so exposing this memory via /sys/firmware/memmap/ = is >>>> wrong: >>>> "kexec needs the raw firmware-provided memory map to setup the >>>> parameter segment of the kernel that should be booted with >>>> kexec. Also, the raw memory map is useful for debugging. For >>>> that reason, /sys/firmware/memmap is an interface that provides >>>> the raw memory map to userspace." [1] >>>> >>>> We don't have to worry about firmware_map_remove() on the removal pa= th. >>>> If there is no entry, it will simply return with -EINVAL. >>>> >>>> [1] >>>> https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-firmware-= memmap >>> >>> >>> You know what this justification is rubbish, and I have previously >>> explained why it is rubbish. >> >> Actually, no, I don't think it is rubbish. See patch #3 and the cover >> letter why this is the right thing to do *for special memory*, *not >> ordinary DIMMs*. >> >> And to be quite honest, I think your response is a little harsh. I don= 't >> recall you replying to my virtio-mem-related comments. >> >>> >>> Nacked-by: "Eric W. Biederman" >>> >>> This needs to be based on weather the added memory is ultimately norm= al >>> ram or is something special. >> >> Yes, that's what the caller are expected to decide, see patch #3. >> >> kexec should try to be as closely as possible to a real reboot - IMHO. >=20 > That is very fuzzy in terms of hotplug memory. The kexec'd kernel > should see the hotplugged memory assuming it is ordinary memory. >=20 > But kexec is not a reboot although it is quite similar. Kexec is > swapping one running kernel and it's state for another kernel without > rebooting. I agree (especially regarding the arm64 DIMM hotplug discussion). However, for the two cases a) dax/kmem b) virtio-mem We really want to let the driver take back control and figure out "what to do with the memory". >=20 >>> Justifying behavior by documentation that does not consider memory >>> hotplug is bad thinking. >> >> Are you maybe confusing this patch series with the arm64 approach? Thi= s >> is not about ordinary hotplugged DIMMs. >=20 > I think I am. >=20 > My challenge is that I don't see anything in the description that says > this isn't about ordinary hotplugged DIMMs. All I saw was hotplug > memory. I'm sorry if that was confusing, I tried to stress that kmem and virtio-mem is special in the description. I squeezed a lot of that information into the cover letter and into patch #3. >=20 > If the class of memory is different then please by all means let's mark > it differently in struct resource so everyone knows it is different. > But that difference needs to be more than hotplug. >=20 > That difference needs to be the hypervisor loaned us memory and might > take it back at any time, or this memory is persistent and so it has > these different characteristics so don't use it as ordinary ram. Yes, and I think kmem took an excellent approach of explicitly putting that "System RAM" into a resource hierarchy. That "System RAM" won't show up as a root node under /proc/iomem (see patch #3), which already results in kexec-tools to treat it in a special way. I am thinking about doing the same for virtio-mem. >=20 > That information is also useful to other people looking at the system > and seeing what is going on. >=20 > Just please don't muddle the concepts, or assume that whatever subset o= f > hotplug memory you are dealing with is the only subset. I can certainly rephrase the subject/description/comment, stating that this is not to be used for ordinary hotplugged DIMMs - only when the device driver is under control to decide what to do with that memory - especially when kexec'ing. (previously, I called this flag MHP_DRIVER_MANAGED, but I think MHP_NO_FIRMWARE_MEMMAP is clearer, we just need a better description) Would that make it clearer? Thanks! --=20 Thanks, David / dhildenb