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 02406C2BA19 for ; Tue, 14 Apr 2020 08:00:19 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9CAE32072D for ; Tue, 14 Apr 2020 08:00:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IJzSMsLs" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9CAE32072D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 34B8F8E0003; Tue, 14 Apr 2020 04:00:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2FB788E0001; Tue, 14 Apr 2020 04:00:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1C38C8E0003; Tue, 14 Apr 2020 04:00:18 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0141.hostedemail.com [216.40.44.141]) by kanga.kvack.org (Postfix) with ESMTP id 05A408E0001 for ; Tue, 14 Apr 2020 04:00:18 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id C648D4FFA for ; Tue, 14 Apr 2020 08:00:17 +0000 (UTC) X-FDA: 76705712874.07.match27_1f9a95404d831 X-HE-Tag: match27_1f9a95404d831 X-Filterd-Recvd-Size: 14036 Received: from us-smtp-delivery-1.mimecast.com (us-smtp-1.mimecast.com [207.211.31.81]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Tue, 14 Apr 2020 08:00:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586851216; 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=69vyvevBf1KIn28IpfF1pAbaOXH/RcttTXTg7fHA63I=; b=IJzSMsLsfXJ0iQESm3glnlxKg4L6bOQc0H0tL+QBFSdJFQGlXfbGjG5q/V0EGtnKN7h6kE G5cDaNIhFh4S1JLVTqdKjR3HvnStOz8xOIWZMlfcofZPrHxZQjPvt/ygMiZ4KChYaiEL+h DZ2cqDpvxWuqZisdzqWuDaYLsZ3AuZg= 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-447-_HqSsyuWP3C8KkGdWmBcRw-1; Tue, 14 Apr 2020 04:00:13 -0400 X-MC-Unique: _HqSsyuWP3C8KkGdWmBcRw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 382328017FC; Tue, 14 Apr 2020 08:00:11 +0000 (UTC) Received: from [10.36.113.201] (ovpn-113-201.ams2.redhat.com [10.36.113.201]) by smtp.corp.redhat.com (Postfix) with ESMTP id 068949F9B2; Tue, 14 Apr 2020 08:00:06 +0000 (UTC) Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image To: Baoquan He , "Eric W. Biederman" Cc: Russell King - ARM Linux admin , Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , kexec@lists.infradead.org, linux-mm@kvack.org, James Morse , Andrew Morton , Will Deacon , linux-arm-kernel@lists.infradead.org References: <20200410121013.03b609fd572504c03a666f4a@linux-foundation.org> <20200411034414.GH2129@MiWiFi-R3L-srv> <20200411093009.GH25745@shell.armlinux.org.uk> <20200412053507.GA4247@MiWiFi-R3L-srv> <20200412080836.GM25745@shell.armlinux.org.uk> <87wo6klbw0.fsf@x220.int.ebiederm.org> <20200413023701.GA20265@MiWiFi-R3L-srv> <871rorjzmc.fsf@x220.int.ebiederm.org> <20200414064031.GB4247@MiWiFi-R3L-srv> 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: <86e96214-7053-340b-5c1a-ff97fb94d8e0@redhat.com> Date: Tue, 14 Apr 2020 10:00:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200414064031.GB4247@MiWiFi-R3L-srv> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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 14.04.20 08:40, Baoquan He wrote: > On 04/13/20 at 08:15am, Eric W. Biederman wrote: >> Baoquan He writes: >> >>> On 04/12/20 at 02:52pm, Eric W. Biederman wrote: >>>> >>>> The only benefit of kexec_file_load is that it is simple enough from a >>>> kernel perspective that signatures can be checked. >>> >>> We don't have this restriction any more with below commit: >>> >>> commit 99d5cadfde2b ("kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG >>> and KEXEC_SIG_FORCE") >>> >>> With KEXEC_SIG_FORCE not set, we can use kexec_load_file to cover both >>> secure boot or legacy system for kexec/kdump. Being simple enough is >>> enough to astract and convince us to use it instead. And kexec_file_loa= d >>> has been in use for several years on systems with secure boot, since >>> added in 2014, on x86_64. >> >> No. Actaully kexec_file_load is the less capable interface, and less >> flexible interface. Which is why it is appropriate for signature >> verification. >=20 > Well, everyone has a stance and the corresponding view. You could have > wider view from long time maintenance and in upstrem position, and think > kexec_file_load is horrible. But I can only see from our work as a front > line engineer to maintain/develop kexec/kdump in RHEL, and think > kexec_file_load is easier to maintain. >=20 > Surely except of multiple kernel image format support. No matter it is > kexec_load and kexec_file_load, e.g in x86_64, we only support bzImage. > This is produced from kerel building by default. We have no way to > support it in our distros and add it into kexec_file_load. >=20 > [RFC PATCH] x86/boot: make ELF kernel multiboot-able > https://lkml.org/lkml/2017/2/15/654 >=20 >> >>>> kexec_load in every other respect is the more capable and functional >>>> interface. It makes no sense to get rid of it. >>>> >>>> It does make sense to reload with a loaded kernel on memory hotplug. >>>> That is simple and easy. If we are going to handle something in the >>>> kernel it should simple an automated unloading of the kernel on memory >>>> hotplug. >>>> >>>> >>>> I think it would be irresponsible to deprecate kexec_load on any >>>> platform. >>>> >>>> I also suspect that kexec_file_load could be taught to copy the dtb >>>> on arm32 if someone wants to deal with signatures. >>>> >>>> We definitely can not even think of deprecating kexec_load until >>>> architecture that supports it also supports kexec_file_load and everyo= ne >>>> is happy with that interface. That is Linus's no regression rule. >>> >>> I should pick a milder word to express our tendency and tell our plan >>> then 'obsolete'. Even though I added 'gradually', seems it doesn't help >>> much. I didn't mean to say 'deprecate' at all when replied. >>> >>> The situation and trend I understand about kexec_load and kexec_file_lo= ad >>> are: >>> >>> 1) Supporting kexec_file_load is suggested to add in ARCHes which don't >>> have yet, just as x86_64, arm64 and s390 have done; >>> =20 >>> 2) kexec_file_load is suggested to use, and take precedence over >>> kexec_load in the future, if both are supported in one ARCH. >> >> The deep problem is that kexec_file_load is distinctly less expressive >> than kexec_load. >> >>> 3) Kexec_load is kept being used by ARCHes w/o kexc_file_load support, >>> and by ARCHes for back compatibility w/ kexec_file_load support. >>> >>> For 1) and 2), I think the reason is obvious as Eric said, >>> kexec_file_load is simple enough. And currently, whenever we got a bug >>> report, we may need fix them twice, for kexec_load and kexec_file_load. >>> If kexec_file_load is made by default, e.g on x86_64, we will change it >>> in kernel space only, for kexec_file_load. This is what I meant about >>> 'obsolete gradually'. I think for arm64, s390, they will do these too. >>> Unless there's some critical/blocker bug in kexec_load, to corrupt the >>> old kexec_load interface in old product. >> >> Maybe. The code that kexec_file_load sucked into the kernel is quite >> stable and rarely needs changes except during a port of kexec to >> another architecture. >> >> Last I looked the real maintenance effor of kexec and kexec on panic was >> in the drivers. So I don't think we can use maintenance to do anything. >=20 > Not sure if I got it. But if check Lianbo's patches, a lot of effort has > been taken to make SEV work well on kexec_file_load. And we have > switched to use kexec_file_load in the newly published Fedora release > on x86_64 by default. Before this, Lianbo has investigated and done many > experiments to make sure the switching is safe. We finally made this > decision. Next we will do the switch in Enterprise distros. Once these > are proved safe, we will suggest customers to use kexec_file_load for > kexec rebooting too. In the future, we will only care about > kexec_file_load if everying is going well. But as I have explained > repeatedly, only caring about kexec_file_load means we will leave > kexec_load as is, we will not add new feature or improvement patches > for it. >=20 > commit 6a20bd54473e11011bf2b47efb52d0759d412854 > Author: Lianbo Jiang > Date: Thu Jan 16 13:47:35 2020 +0800 >=20 > kdump-lib: switch to the kexec_file_load() syscall on x86_64 by defau= lt >=20 >> >>> For 3), people can still use kexec_load and develop/fix for it, if no >>> kexec_file_load supported. But 32-bit arm should be a different one, >>> more like i386, we will leave it as is, and fix anything which could >>> break it. But people really expects to improve or add feature to it? E.= g >>> in this patchset, the mem hotplug issue James raised, I assume James is >>> focusing on arm64, x86_64, but not 32-bit arm. As DavidH commented in >>> another reply, people even don't agree to continue supporting memory >>> hotplug on 32-bit system. We ever took effort to fix a memory hotplug >>> bug on i386 with a patch, but people would rather set it as BROKEN. >> >> For memory hotplug just reload. Userspace already gets good events. >=20 > Kexec_file_load is easy to maintain. This is an example. >=20 > Lock the hotplug area where kexed-ed kernel is targeted in this patchset, > it's obviously not right. We can't disable memory hotplug just because > kexec-ed kernel is loaded ahead of time.=20 >=20 > Reloading is also not a good fix. Kexec-ed kernel is targeted at a > movable area, reloading can avoid kexec rebooting corruption if that > area is hot removed. But if that area is not removed, locating kernel > into the hotpluggable area will change the area into ummovable zone. > Unless we decide to not support memory hotplug in kexec-ed kernel, I > guess it's very hard. Now in our distros kexec rebooting has been > supported, the big cloud providers are deploying linux in guest, bugs on > kexec reboot failure has been reported. They need the memory hotplug to > increase/decrease memory. >=20 > The root cause is kexec-ed kernel is targeted at hotpluggable memory > region. Just avoiding the movable area can fix it. In kexec_file_load(), > just checking or picking those unmovable region to put kernel/initrd in > function locate_mem_hole_callback() can fix it. The page or pageblock's > zone is movable or not, it's easy to know. This fix doesn't need to > bother other component. I don't fully agree. E.g., just because memory is onlined to ZONE_NORMAL does not imply that it cannot get offlined and removed e.g., this is heavily used on ppc64, with 16MB sections. --=20 Thanks, David / dhildenb 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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 ED981C2BA19 for ; Tue, 14 Apr 2020 08:00:35 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B84CE2074D for ; Tue, 14 Apr 2020 08:00:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="QlK2CT3l"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IJzSMsLs" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B84CE2074D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:To:Subject:Reply-To:Content-ID:Content-Description :Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=m90CiDSgKhuAk4DCa2jV0XoPB4as1xzuviDBPwWhmHg=; b=QlK2CT3l0TY+Z6 IFA+k1F6CzTq9AWe7peGjQ8MDMG5eSimEHN+o0c+jaKQDosNwgp6m3KM+l5T8jtSImvZgrmGGnuE9 +a5wWUv6O3nYAzNhRXed/AWC3TtyOvU+IVpWtWxpAn7GuhrcyHv0z0zYbjhmd0puKeCm5O7mPpVGK 7gJUO9EkSBjzFLZ/XVpmTtE3kt1P5B5QQv4vF9HI1hb84xAlvdiVLrxr+zCjAFamb/iOQwvMFrGVU ecnJLK7YvS7fE44UkBdS/0W7Mv7w4+eIhPxSkEHOgjUrMquHor/4dwqL2JhJHHxLeQiI+dWEeVWAk l7GXZgR+467Uop1NxU2Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jOGUk-0003fw-MP; Tue, 14 Apr 2020 08:00:34 +0000 Received: from us-smtp-2.mimecast.com ([207.211.31.81] helo=us-smtp-delivery-1.mimecast.com) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jOGUT-0003PT-Mo for linux-arm-kernel@lists.infradead.org; Tue, 14 Apr 2020 08:00:20 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586851216; 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=69vyvevBf1KIn28IpfF1pAbaOXH/RcttTXTg7fHA63I=; b=IJzSMsLsfXJ0iQESm3glnlxKg4L6bOQc0H0tL+QBFSdJFQGlXfbGjG5q/V0EGtnKN7h6kE G5cDaNIhFh4S1JLVTqdKjR3HvnStOz8xOIWZMlfcofZPrHxZQjPvt/ygMiZ4KChYaiEL+h DZ2cqDpvxWuqZisdzqWuDaYLsZ3AuZg= 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-447-_HqSsyuWP3C8KkGdWmBcRw-1; Tue, 14 Apr 2020 04:00:13 -0400 X-MC-Unique: _HqSsyuWP3C8KkGdWmBcRw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 382328017FC; Tue, 14 Apr 2020 08:00:11 +0000 (UTC) Received: from [10.36.113.201] (ovpn-113-201.ams2.redhat.com [10.36.113.201]) by smtp.corp.redhat.com (Postfix) with ESMTP id 068949F9B2; Tue, 14 Apr 2020 08:00:06 +0000 (UTC) Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image To: Baoquan He , "Eric W. Biederman" References: <20200410121013.03b609fd572504c03a666f4a@linux-foundation.org> <20200411034414.GH2129@MiWiFi-R3L-srv> <20200411093009.GH25745@shell.armlinux.org.uk> <20200412053507.GA4247@MiWiFi-R3L-srv> <20200412080836.GM25745@shell.armlinux.org.uk> <87wo6klbw0.fsf@x220.int.ebiederm.org> <20200413023701.GA20265@MiWiFi-R3L-srv> <871rorjzmc.fsf@x220.int.ebiederm.org> <20200414064031.GB4247@MiWiFi-R3L-srv> 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: <86e96214-7053-340b-5c1a-ff97fb94d8e0@redhat.com> Date: Tue, 14 Apr 2020 10:00:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200414064031.GB4247@MiWiFi-R3L-srv> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200414_010017_828655_651DFB59 X-CRM114-Status: GOOD ( 35.13 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , kexec@lists.infradead.org, Russell King - ARM Linux admin , linux-mm@kvack.org, James Morse , Andrew Morton , Will Deacon , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 14.04.20 08:40, Baoquan He wrote: > On 04/13/20 at 08:15am, Eric W. Biederman wrote: >> Baoquan He writes: >> >>> On 04/12/20 at 02:52pm, Eric W. Biederman wrote: >>>> >>>> The only benefit of kexec_file_load is that it is simple enough from a >>>> kernel perspective that signatures can be checked. >>> >>> We don't have this restriction any more with below commit: >>> >>> commit 99d5cadfde2b ("kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG >>> and KEXEC_SIG_FORCE") >>> >>> With KEXEC_SIG_FORCE not set, we can use kexec_load_file to cover both >>> secure boot or legacy system for kexec/kdump. Being simple enough is >>> enough to astract and convince us to use it instead. And kexec_file_load >>> has been in use for several years on systems with secure boot, since >>> added in 2014, on x86_64. >> >> No. Actaully kexec_file_load is the less capable interface, and less >> flexible interface. Which is why it is appropriate for signature >> verification. > > Well, everyone has a stance and the corresponding view. You could have > wider view from long time maintenance and in upstrem position, and think > kexec_file_load is horrible. But I can only see from our work as a front > line engineer to maintain/develop kexec/kdump in RHEL, and think > kexec_file_load is easier to maintain. > > Surely except of multiple kernel image format support. No matter it is > kexec_load and kexec_file_load, e.g in x86_64, we only support bzImage. > This is produced from kerel building by default. We have no way to > support it in our distros and add it into kexec_file_load. > > [RFC PATCH] x86/boot: make ELF kernel multiboot-able > https://lkml.org/lkml/2017/2/15/654 > >> >>>> kexec_load in every other respect is the more capable and functional >>>> interface. It makes no sense to get rid of it. >>>> >>>> It does make sense to reload with a loaded kernel on memory hotplug. >>>> That is simple and easy. If we are going to handle something in the >>>> kernel it should simple an automated unloading of the kernel on memory >>>> hotplug. >>>> >>>> >>>> I think it would be irresponsible to deprecate kexec_load on any >>>> platform. >>>> >>>> I also suspect that kexec_file_load could be taught to copy the dtb >>>> on arm32 if someone wants to deal with signatures. >>>> >>>> We definitely can not even think of deprecating kexec_load until >>>> architecture that supports it also supports kexec_file_load and everyone >>>> is happy with that interface. That is Linus's no regression rule. >>> >>> I should pick a milder word to express our tendency and tell our plan >>> then 'obsolete'. Even though I added 'gradually', seems it doesn't help >>> much. I didn't mean to say 'deprecate' at all when replied. >>> >>> The situation and trend I understand about kexec_load and kexec_file_load >>> are: >>> >>> 1) Supporting kexec_file_load is suggested to add in ARCHes which don't >>> have yet, just as x86_64, arm64 and s390 have done; >>> >>> 2) kexec_file_load is suggested to use, and take precedence over >>> kexec_load in the future, if both are supported in one ARCH. >> >> The deep problem is that kexec_file_load is distinctly less expressive >> than kexec_load. >> >>> 3) Kexec_load is kept being used by ARCHes w/o kexc_file_load support, >>> and by ARCHes for back compatibility w/ kexec_file_load support. >>> >>> For 1) and 2), I think the reason is obvious as Eric said, >>> kexec_file_load is simple enough. And currently, whenever we got a bug >>> report, we may need fix them twice, for kexec_load and kexec_file_load. >>> If kexec_file_load is made by default, e.g on x86_64, we will change it >>> in kernel space only, for kexec_file_load. This is what I meant about >>> 'obsolete gradually'. I think for arm64, s390, they will do these too. >>> Unless there's some critical/blocker bug in kexec_load, to corrupt the >>> old kexec_load interface in old product. >> >> Maybe. The code that kexec_file_load sucked into the kernel is quite >> stable and rarely needs changes except during a port of kexec to >> another architecture. >> >> Last I looked the real maintenance effor of kexec and kexec on panic was >> in the drivers. So I don't think we can use maintenance to do anything. > > Not sure if I got it. But if check Lianbo's patches, a lot of effort has > been taken to make SEV work well on kexec_file_load. And we have > switched to use kexec_file_load in the newly published Fedora release > on x86_64 by default. Before this, Lianbo has investigated and done many > experiments to make sure the switching is safe. We finally made this > decision. Next we will do the switch in Enterprise distros. Once these > are proved safe, we will suggest customers to use kexec_file_load for > kexec rebooting too. In the future, we will only care about > kexec_file_load if everying is going well. But as I have explained > repeatedly, only caring about kexec_file_load means we will leave > kexec_load as is, we will not add new feature or improvement patches > for it. > > commit 6a20bd54473e11011bf2b47efb52d0759d412854 > Author: Lianbo Jiang > Date: Thu Jan 16 13:47:35 2020 +0800 > > kdump-lib: switch to the kexec_file_load() syscall on x86_64 by default > >> >>> For 3), people can still use kexec_load and develop/fix for it, if no >>> kexec_file_load supported. But 32-bit arm should be a different one, >>> more like i386, we will leave it as is, and fix anything which could >>> break it. But people really expects to improve or add feature to it? E.g >>> in this patchset, the mem hotplug issue James raised, I assume James is >>> focusing on arm64, x86_64, but not 32-bit arm. As DavidH commented in >>> another reply, people even don't agree to continue supporting memory >>> hotplug on 32-bit system. We ever took effort to fix a memory hotplug >>> bug on i386 with a patch, but people would rather set it as BROKEN. >> >> For memory hotplug just reload. Userspace already gets good events. > > Kexec_file_load is easy to maintain. This is an example. > > Lock the hotplug area where kexed-ed kernel is targeted in this patchset, > it's obviously not right. We can't disable memory hotplug just because > kexec-ed kernel is loaded ahead of time. > > Reloading is also not a good fix. Kexec-ed kernel is targeted at a > movable area, reloading can avoid kexec rebooting corruption if that > area is hot removed. But if that area is not removed, locating kernel > into the hotpluggable area will change the area into ummovable zone. > Unless we decide to not support memory hotplug in kexec-ed kernel, I > guess it's very hard. Now in our distros kexec rebooting has been > supported, the big cloud providers are deploying linux in guest, bugs on > kexec reboot failure has been reported. They need the memory hotplug to > increase/decrease memory. > > The root cause is kexec-ed kernel is targeted at hotpluggable memory > region. Just avoiding the movable area can fix it. In kexec_file_load(), > just checking or picking those unmovable region to put kernel/initrd in > function locate_mem_hole_callback() can fix it. The page or pageblock's > zone is movable or not, it's easy to know. This fix doesn't need to > bother other component. I don't fully agree. E.g., just because memory is onlined to ZONE_NORMAL does not imply that it cannot get offlined and removed e.g., this is heavily used on ppc64, with 16MB sections. -- Thanks, David / dhildenb _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from us-smtp-1.mimecast.com ([207.211.31.81] helo=us-smtp-delivery-1.mimecast.com) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jOGUT-0003LZ-Mo for kexec@lists.infradead.org; Tue, 14 Apr 2020 08:00:19 +0000 Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image References: <20200410121013.03b609fd572504c03a666f4a@linux-foundation.org> <20200411034414.GH2129@MiWiFi-R3L-srv> <20200411093009.GH25745@shell.armlinux.org.uk> <20200412053507.GA4247@MiWiFi-R3L-srv> <20200412080836.GM25745@shell.armlinux.org.uk> <87wo6klbw0.fsf@x220.int.ebiederm.org> <20200413023701.GA20265@MiWiFi-R3L-srv> <871rorjzmc.fsf@x220.int.ebiederm.org> <20200414064031.GB4247@MiWiFi-R3L-srv> From: David Hildenbrand Message-ID: <86e96214-7053-340b-5c1a-ff97fb94d8e0@redhat.com> Date: Tue, 14 Apr 2020 10:00:06 +0200 MIME-Version: 1.0 In-Reply-To: <20200414064031.GB4247@MiWiFi-R3L-srv> Content-Language: en-US List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Baoquan He , "Eric W. Biederman" Cc: Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , kexec@lists.infradead.org, Russell King - ARM Linux admin , linux-mm@kvack.org, James Morse , Andrew Morton , Will Deacon , linux-arm-kernel@lists.infradead.org On 14.04.20 08:40, Baoquan He wrote: > On 04/13/20 at 08:15am, Eric W. Biederman wrote: >> Baoquan He writes: >> >>> On 04/12/20 at 02:52pm, Eric W. Biederman wrote: >>>> >>>> The only benefit of kexec_file_load is that it is simple enough from a >>>> kernel perspective that signatures can be checked. >>> >>> We don't have this restriction any more with below commit: >>> >>> commit 99d5cadfde2b ("kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG >>> and KEXEC_SIG_FORCE") >>> >>> With KEXEC_SIG_FORCE not set, we can use kexec_load_file to cover both >>> secure boot or legacy system for kexec/kdump. Being simple enough is >>> enough to astract and convince us to use it instead. And kexec_file_load >>> has been in use for several years on systems with secure boot, since >>> added in 2014, on x86_64. >> >> No. Actaully kexec_file_load is the less capable interface, and less >> flexible interface. Which is why it is appropriate for signature >> verification. > > Well, everyone has a stance and the corresponding view. You could have > wider view from long time maintenance and in upstrem position, and think > kexec_file_load is horrible. But I can only see from our work as a front > line engineer to maintain/develop kexec/kdump in RHEL, and think > kexec_file_load is easier to maintain. > > Surely except of multiple kernel image format support. No matter it is > kexec_load and kexec_file_load, e.g in x86_64, we only support bzImage. > This is produced from kerel building by default. We have no way to > support it in our distros and add it into kexec_file_load. > > [RFC PATCH] x86/boot: make ELF kernel multiboot-able > https://lkml.org/lkml/2017/2/15/654 > >> >>>> kexec_load in every other respect is the more capable and functional >>>> interface. It makes no sense to get rid of it. >>>> >>>> It does make sense to reload with a loaded kernel on memory hotplug. >>>> That is simple and easy. If we are going to handle something in the >>>> kernel it should simple an automated unloading of the kernel on memory >>>> hotplug. >>>> >>>> >>>> I think it would be irresponsible to deprecate kexec_load on any >>>> platform. >>>> >>>> I also suspect that kexec_file_load could be taught to copy the dtb >>>> on arm32 if someone wants to deal with signatures. >>>> >>>> We definitely can not even think of deprecating kexec_load until >>>> architecture that supports it also supports kexec_file_load and everyone >>>> is happy with that interface. That is Linus's no regression rule. >>> >>> I should pick a milder word to express our tendency and tell our plan >>> then 'obsolete'. Even though I added 'gradually', seems it doesn't help >>> much. I didn't mean to say 'deprecate' at all when replied. >>> >>> The situation and trend I understand about kexec_load and kexec_file_load >>> are: >>> >>> 1) Supporting kexec_file_load is suggested to add in ARCHes which don't >>> have yet, just as x86_64, arm64 and s390 have done; >>> >>> 2) kexec_file_load is suggested to use, and take precedence over >>> kexec_load in the future, if both are supported in one ARCH. >> >> The deep problem is that kexec_file_load is distinctly less expressive >> than kexec_load. >> >>> 3) Kexec_load is kept being used by ARCHes w/o kexc_file_load support, >>> and by ARCHes for back compatibility w/ kexec_file_load support. >>> >>> For 1) and 2), I think the reason is obvious as Eric said, >>> kexec_file_load is simple enough. And currently, whenever we got a bug >>> report, we may need fix them twice, for kexec_load and kexec_file_load. >>> If kexec_file_load is made by default, e.g on x86_64, we will change it >>> in kernel space only, for kexec_file_load. This is what I meant about >>> 'obsolete gradually'. I think for arm64, s390, they will do these too. >>> Unless there's some critical/blocker bug in kexec_load, to corrupt the >>> old kexec_load interface in old product. >> >> Maybe. The code that kexec_file_load sucked into the kernel is quite >> stable and rarely needs changes except during a port of kexec to >> another architecture. >> >> Last I looked the real maintenance effor of kexec and kexec on panic was >> in the drivers. So I don't think we can use maintenance to do anything. > > Not sure if I got it. But if check Lianbo's patches, a lot of effort has > been taken to make SEV work well on kexec_file_load. And we have > switched to use kexec_file_load in the newly published Fedora release > on x86_64 by default. Before this, Lianbo has investigated and done many > experiments to make sure the switching is safe. We finally made this > decision. Next we will do the switch in Enterprise distros. Once these > are proved safe, we will suggest customers to use kexec_file_load for > kexec rebooting too. In the future, we will only care about > kexec_file_load if everying is going well. But as I have explained > repeatedly, only caring about kexec_file_load means we will leave > kexec_load as is, we will not add new feature or improvement patches > for it. > > commit 6a20bd54473e11011bf2b47efb52d0759d412854 > Author: Lianbo Jiang > Date: Thu Jan 16 13:47:35 2020 +0800 > > kdump-lib: switch to the kexec_file_load() syscall on x86_64 by default > >> >>> For 3), people can still use kexec_load and develop/fix for it, if no >>> kexec_file_load supported. But 32-bit arm should be a different one, >>> more like i386, we will leave it as is, and fix anything which could >>> break it. But people really expects to improve or add feature to it? E.g >>> in this patchset, the mem hotplug issue James raised, I assume James is >>> focusing on arm64, x86_64, but not 32-bit arm. As DavidH commented in >>> another reply, people even don't agree to continue supporting memory >>> hotplug on 32-bit system. We ever took effort to fix a memory hotplug >>> bug on i386 with a patch, but people would rather set it as BROKEN. >> >> For memory hotplug just reload. Userspace already gets good events. > > Kexec_file_load is easy to maintain. This is an example. > > Lock the hotplug area where kexed-ed kernel is targeted in this patchset, > it's obviously not right. We can't disable memory hotplug just because > kexec-ed kernel is loaded ahead of time. > > Reloading is also not a good fix. Kexec-ed kernel is targeted at a > movable area, reloading can avoid kexec rebooting corruption if that > area is hot removed. But if that area is not removed, locating kernel > into the hotpluggable area will change the area into ummovable zone. > Unless we decide to not support memory hotplug in kexec-ed kernel, I > guess it's very hard. Now in our distros kexec rebooting has been > supported, the big cloud providers are deploying linux in guest, bugs on > kexec reboot failure has been reported. They need the memory hotplug to > increase/decrease memory. > > The root cause is kexec-ed kernel is targeted at hotpluggable memory > region. Just avoiding the movable area can fix it. In kexec_file_load(), > just checking or picking those unmovable region to put kernel/initrd in > function locate_mem_hole_callback() can fix it. The page or pageblock's > zone is movable or not, it's easy to know. This fix doesn't need to > bother other component. I don't fully agree. E.g., just because memory is onlined to ZONE_NORMAL does not imply that it cannot get offlined and removed e.g., this is heavily used on ppc64, with 16MB sections. -- Thanks, David / dhildenb _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec