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,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 A98A5C2BA19 for ; Tue, 14 Apr 2020 09:37:11 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4A77020644 for ; Tue, 14 Apr 2020 09:37:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Zjxkw3D3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4A77020644 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 D63108E0003; Tue, 14 Apr 2020 05:37:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D140E8E0001; Tue, 14 Apr 2020 05:37:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C02BC8E0003; Tue, 14 Apr 2020 05:37:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0180.hostedemail.com [216.40.44.180]) by kanga.kvack.org (Postfix) with ESMTP id A96C38E0001 for ; Tue, 14 Apr 2020 05:37:10 -0400 (EDT) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 667108245571 for ; Tue, 14 Apr 2020 09:37:10 +0000 (UTC) X-FDA: 76705957020.09.music06_45916d1ef623 X-HE-Tag: music06_45916d1ef623 X-Filterd-Recvd-Size: 15672 Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [207.211.31.120]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Tue, 14 Apr 2020 09:37:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586857029; 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=F+e8d31+yFHyW+PwzGSt59ZUTL7KnqXHNqi9QCkJoK8=; b=Zjxkw3D3Sq8SemRMqajf53gtI/+9pys3Fhsq+49ctyx9Vn5NIsGOjdZOn1md9aZM2grY6E Hocue/uL84uwMysPHsEdtg0riX1+UMTaLNfv2ZGwoUXwtDxYyWpsbEq8UaempQRjaEdLZo eX0XTVDqOonspqN0GJx0URcsYztfOb4= 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-411-10XFZthZP1qQl-MIZU0g0w-1; Tue, 14 Apr 2020 05:37:07 -0400 X-MC-Unique: 10XFZthZP1qQl-MIZU0g0w-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 E44FB1926DA4; Tue, 14 Apr 2020 09:37:05 +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 DC0235C1B5; Tue, 14 Apr 2020 09:37:02 +0000 (UTC) Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image To: Baoquan He Cc: "Eric W. Biederman" , 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, linuxppc-dev@lists.ozlabs.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> <86e96214-7053-340b-5c1a-ff97fb94d8e0@redhat.com> <20200414092201.GD4247@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: Date: Tue, 14 Apr 2020 11:37:01 +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: <20200414092201.GD4247@MiWiFi-R3L-srv> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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 11:22, Baoquan He wrote: > On 04/14/20 at 10:00am, David Hildenbrand wrote: >> 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_S= IG >>>>> and KEXEC_SIG_FORCE") >>>>> >>>>> With KEXEC_SIG_FORCE not set, we can use kexec_load_file to cover bot= h >>>>> 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_l= oad >>>>> 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 thin= k >>> kexec_file_load is horrible. But I can only see from our work as a fron= t >>> 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 memo= ry >>>>>> 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 ever= yone >>>>>> 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 he= lp >>>>> 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; >>>>> =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 bu= g >>>>> report, we may need fix them twice, for kexec_load and kexec_file_loa= d. >>>>> 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 th= e >>>>> 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 w= as >>>> in the drivers. So I don't think we can use maintenance to do anythin= g. >>> >>> Not sure if I got it. But if check Lianbo's patches, a lot of effort ha= s >>> 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 man= y >>> 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 def= ault >>> >>>> >>>>> 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 patchse= t, >>> it's obviously not right. We can't disable memory hotplug just because >>> kexec-ed kernel is loaded ahead of time.=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 o= n >>> 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. >=20 > Really? I just know there are two kinds of mem hoplug in ppc, but don't > know the details. So in this case, is there any flag or a way to know > those memory block are hotpluggable? I am curious how those kernel data > is avoided to be put in this area. Or ppc just freely uses it for kernel > data or user space data, then try to migrate when hot remove? See arch/powerpc/platforms/pseries/hotplug-memory.c:dlpar_memory_remove_by_coun= t() Under DLAPR, it can remove memory in LMB granularity, which is usually 16MB (=3D=3D single section on ppc64). DLPAR will directly online all hotplugged memory (LMBs) from the kernel using device_online(), which will go to ZONE_NORMAL. When trying to remove memory, it simply scans for offlineable 16MB memory blocks (=3D=3Dsection =3D=3D LMB), offlines and removes them. No nee= d for the movable zone and all the involved issues. Now, the interesting question is, can we have LMBs added during boot (not via add_memory()), that will later be removed via remove_memory(). IIRC, we had BUGs related to that, so I think yes. If a section contains no unmovable allocations (after boot), it can get removed. --=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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 314E9C2BA19 for ; Tue, 14 Apr 2020 09:38:53 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 731A320644 for ; Tue, 14 Apr 2020 09:38:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Zjxkw3D3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 731A320644 Authentication-Results: mail.kernel.org; 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Tue, 14 Apr 2020 09:37:05 +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 DC0235C1B5; Tue, 14 Apr 2020 09:37:02 +0000 (UTC) Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image To: Baoquan He 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> <86e96214-7053-340b-5c1a-ff97fb94d8e0@redhat.com> <20200414092201.GD4247@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: Date: Tue, 14 Apr 2020 11:37:01 +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: <20200414092201.GD4247@MiWiFi-R3L-srv> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , linuxppc-dev@lists.ozlabs.org, kexec@lists.infradead.org, Russell King - ARM Linux admin , linux-mm@kvack.org, James Morse , "Eric W. Biederman" , Andrew Morton , Will Deacon , linux-arm-kernel@lists.infradead.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 14.04.20 11:22, Baoquan He wrote: > On 04/14/20 at 10:00am, David Hildenbrand wrote: >> 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_S= IG >>>>> and KEXEC_SIG_FORCE") >>>>> >>>>> With KEXEC_SIG_FORCE not set, we can use kexec_load_file to cover bot= h >>>>> 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_l= oad >>>>> 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 thin= k >>> kexec_file_load is horrible. But I can only see from our work as a fron= t >>> 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 memo= ry >>>>>> 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 ever= yone >>>>>> 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 he= lp >>>>> 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; >>>>> =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 bu= g >>>>> report, we may need fix them twice, for kexec_load and kexec_file_loa= d. >>>>> 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 th= e >>>>> 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 w= as >>>> in the drivers. So I don't think we can use maintenance to do anythin= g. >>> >>> Not sure if I got it. But if check Lianbo's patches, a lot of effort ha= s >>> 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 man= y >>> 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 def= ault >>> >>>> >>>>> 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 patchse= t, >>> it's obviously not right. We can't disable memory hotplug just because >>> kexec-ed kernel is loaded ahead of time.=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 o= n >>> 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. >=20 > Really? I just know there are two kinds of mem hoplug in ppc, but don't > know the details. So in this case, is there any flag or a way to know > those memory block are hotpluggable? I am curious how those kernel data > is avoided to be put in this area. Or ppc just freely uses it for kernel > data or user space data, then try to migrate when hot remove? See arch/powerpc/platforms/pseries/hotplug-memory.c:dlpar_memory_remove_by_coun= t() Under DLAPR, it can remove memory in LMB granularity, which is usually 16MB (=3D=3D single section on ppc64). DLPAR will directly online all hotplugged memory (LMBs) from the kernel using device_online(), which will go to ZONE_NORMAL. When trying to remove memory, it simply scans for offlineable 16MB memory blocks (=3D=3Dsection =3D=3D LMB), offlines and removes them. No nee= d for the movable zone and all the involved issues. Now, the interesting question is, can we have LMBs added during boot (not via add_memory()), that will later be removed via remove_memory(). IIRC, we had BUGs related to that, so I think yes. If a section contains no unmovable allocations (after boot), it can get removed. --=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 38A89C2BA19 for ; Tue, 14 Apr 2020 09:37:20 +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 036C120644 for ; Tue, 14 Apr 2020 09:37:20 +0000 (UTC) Authentication-Results: mail.kernel.org; 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bh=F+e8d31+yFHyW+PwzGSt59ZUTL7KnqXHNqi9QCkJoK8=; b=TAKNCzTtsf7cszzwR6vH+Qax6b/UUGygbMOnGRtb68orli8n+prRqSpE5J7iNAYWwKcqc5 CIjBaBUEOw0/4EwqEY1v6UPfZ5B8pwMlbnNu8fVs/6pTwDOD1AC0gxvt2JBp/xVxxTflqJ GDqgdY3jNwn7x2EoCM/jiZzBKSWwzEA= 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-411-10XFZthZP1qQl-MIZU0g0w-1; Tue, 14 Apr 2020 05:37:07 -0400 X-MC-Unique: 10XFZthZP1qQl-MIZU0g0w-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 E44FB1926DA4; Tue, 14 Apr 2020 09:37:05 +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 DC0235C1B5; Tue, 14 Apr 2020 09:37:02 +0000 (UTC) Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image To: Baoquan He 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> <86e96214-7053-340b-5c1a-ff97fb94d8e0@redhat.com> <20200414092201.GD4247@MiWiFi-R3L-srv> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200414092201.GD4247@MiWiFi-R3L-srv> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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_023712_979339_F6CC596E X-CRM114-Status: GOOD ( 31.68 ) 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 , linuxppc-dev@lists.ozlabs.org, kexec@lists.infradead.org, Russell King - ARM Linux admin , linux-mm@kvack.org, James Morse , "Eric W. Biederman" , 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 11:22, Baoquan He wrote: > On 04/14/20 at 10:00am, David Hildenbrand wrote: >> 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. > > Really? I just know there are two kinds of mem hoplug in ppc, but don't > know the details. So in this case, is there any flag or a way to know > those memory block are hotpluggable? I am curious how those kernel data > is avoided to be put in this area. Or ppc just freely uses it for kernel > data or user space data, then try to migrate when hot remove? See arch/powerpc/platforms/pseries/hotplug-memory.c:dlpar_memory_remove_by_count() Under DLAPR, it can remove memory in LMB granularity, which is usually 16MB (== single section on ppc64). DLPAR will directly online all hotplugged memory (LMBs) from the kernel using device_online(), which will go to ZONE_NORMAL. When trying to remove memory, it simply scans for offlineable 16MB memory blocks (==section == LMB), offlines and removes them. No need for the movable zone and all the involved issues. Now, the interesting question is, can we have LMBs added during boot (not via add_memory()), that will later be removed via remove_memory(). IIRC, we had BUGs related to that, so I think yes. If a section contains no unmovable allocations (after boot), it can get removed. -- 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-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 1jOI0G-0002Au-Ov for kexec@lists.infradead.org; Tue, 14 Apr 2020 09:37:14 +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> <86e96214-7053-340b-5c1a-ff97fb94d8e0@redhat.com> <20200414092201.GD4247@MiWiFi-R3L-srv> From: David Hildenbrand Message-ID: Date: Tue, 14 Apr 2020 11:37:01 +0200 MIME-Version: 1.0 In-Reply-To: <20200414092201.GD4247@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 Cc: Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , linuxppc-dev@lists.ozlabs.org, kexec@lists.infradead.org, Russell King - ARM Linux admin , linux-mm@kvack.org, James Morse , "Eric W. Biederman" , Andrew Morton , Will Deacon , linux-arm-kernel@lists.infradead.org On 14.04.20 11:22, Baoquan He wrote: > On 04/14/20 at 10:00am, David Hildenbrand wrote: >> 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. > > Really? I just know there are two kinds of mem hoplug in ppc, but don't > know the details. So in this case, is there any flag or a way to know > those memory block are hotpluggable? I am curious how those kernel data > is avoided to be put in this area. Or ppc just freely uses it for kernel > data or user space data, then try to migrate when hot remove? See arch/powerpc/platforms/pseries/hotplug-memory.c:dlpar_memory_remove_by_count() Under DLAPR, it can remove memory in LMB granularity, which is usually 16MB (== single section on ppc64). DLPAR will directly online all hotplugged memory (LMBs) from the kernel using device_online(), which will go to ZONE_NORMAL. When trying to remove memory, it simply scans for offlineable 16MB memory blocks (==section == LMB), offlines and removes them. No need for the movable zone and all the involved issues. Now, the interesting question is, can we have LMBs added during boot (not via add_memory()), that will later be removed via remove_memory(). IIRC, we had BUGs related to that, so I think yes. If a section contains no unmovable allocations (after boot), it can get removed. -- Thanks, David / dhildenb _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec