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 657B7C2BA1A for ; Fri, 24 Apr 2020 07:39:36 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1B7D420724 for ; Fri, 24 Apr 2020 07:39:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VPM5DtZD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1B7D420724 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 962DC8E0005; Fri, 24 Apr 2020 03:39:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 912718E0003; Fri, 24 Apr 2020 03:39:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7DA1E8E0005; Fri, 24 Apr 2020 03:39:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0137.hostedemail.com [216.40.44.137]) by kanga.kvack.org (Postfix) with ESMTP id 662038E0003 for ; Fri, 24 Apr 2020 03:39:35 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 25DF6180AD81D for ; Fri, 24 Apr 2020 07:39:35 +0000 (UTC) X-FDA: 76741948710.07.beam26_8dd74ba701a10 X-HE-Tag: beam26_8dd74ba701a10 X-Filterd-Recvd-Size: 9838 Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [205.139.110.120]) by imf14.hostedemail.com (Postfix) with ESMTP for ; Fri, 24 Apr 2020 07:39:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587713974; 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=aNxlKYwgJG4hi61htBIsmsJO7dK9IBMS50zV2gyXdls=; b=VPM5DtZDyTtF9pIoLxr0J9C6D6M5hjz+eIJmOM4xIK4oPr3QW8P7Xy7fqkR3padeDkQQ01 EWjyWnvfFK33QFuGg29O3COl9gCX7tGsMtWUomCxIOgXynLWBMOFcWb3L1dz5W4s2dYjqq SB8o1vrh28nMxd9GyuRNEExatQsYxc8= 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-470-RfVNamZaMp2cTOrg0kCeAA-1; Fri, 24 Apr 2020 03:39:30 -0400 X-MC-Unique: RfVNamZaMp2cTOrg0kCeAA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E926D461; Fri, 24 Apr 2020 07:39:28 +0000 (UTC) Received: from [10.36.113.138] (ovpn-113-138.ams2.redhat.com [10.36.113.138]) by smtp.corp.redhat.com (Postfix) with ESMTP id A049D600E8; Fri, 24 Apr 2020 07:39:26 +0000 (UTC) Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image To: "Eric W. Biederman" Cc: James Morse , kexec@lists.infradead.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , Andrew Morton , Will Deacon References: <20200326180730.4754-1-james.morse@arm.com> <20200326180730.4754-2-james.morse@arm.com> <87d088h4k8.fsf@x220.int.ebiederm.org> <87y2qn1r18.fsf@x220.int.ebiederm.org> <87ftcuxj1a.fsf@x220.int.ebiederm.org> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: <4ca41c5f-4cbf-342c-528a-d274c4e2ca10@redhat.com> Date: Fri, 24 Apr 2020 09:39:25 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <87ftcuxj1a.fsf@x220.int.ebiederm.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=windows-1252 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 23.04.20 18:29, Eric W. Biederman wrote: > David Hildenbrand writes: >=20 >>> The confusing part was talking about memory being still in use, >>> that is actually scheduled for use in the future. >> >> +1 >> >>> >>>>> Usually somewhere in the loaded image >>>>> is a copy of the memory map at the time the kexec kernel was loaded. >>>>> That will invalidate the memory map as well. >>>> >>>> Ah, unconditionally. Sure, x86 needs this. >>>> (arm64 re-discovers the memory map from firmware tables after kexec) >> >> Does this include hotplugged DIMMs e.g., under KVM? >> [...] >=20 > As far as I know. If the memory map changes we need to drop the loaded > image. >=20 >=20 > Having thought about it a little more I suspect it would be the > other way and just block all hotplug actions after a kexec_load. > As all we expect to happen is running shutdown scripts. >=20 > If blocking the hotplug action uses printk to print a nice message > saying something like: "Hotplug blocked because of a loaded kexec image", > then people will be able to figure out what is going on and > call kexec -u if they haven't started the shutdown scripts yet. >=20 >=20 > Either way it is something simple and unconditional that will make > things work. >=20 Personally, I consider memory hotplug more important than keeping loaded kexec data alive (just because somebody once decided to do a "kexec -l" and never did a "kexec -e" we should not block any memory hot(un)plug - especially in virtualized environments - for all eternity). So IMHO we would invalidate loaded kexec data (not the crashkernel, of course) on memory hot(un)plug and print a warning. In addition, we can let kexec-tools try to reload whatever they loaded after getting notified that something changed. The "something changed" is visible to user space e.g., via udev events for /sys/devices/memory/memoryX/ >>>>> All of this should be for a very brief window of a few seconds, as >>>>> the loaded kexec image is quite short. >>>> >>>> It seems I'm the outlier anticipating anything could happen between >>>> those syscalls. >>> >>> The design is: >>> =09sys_kexec_load() >>> =09shutdown scripts >>> sys_reboot(LINUX_REBOOT_CMD_KEXEC); >>> >>> There are two system call simply so that the shutdown scripts can run. >>> Now maybe someone somewhere does something different but that is not >>> expected. >>> >>> Only the kexec on panic kernel is expected to persist somewhat >>> indefinitely. But that should be in memory that is reserved from boot >>> time, and so the memory hotplug should have enough visibility to not >>> allow that memory to be given up. >> >> Yes, and AFAIK, memory blocks which hold the reserved crashkernel area >> can usually not get offlined and, therefore, the memory cannot get remov= ed. >> >> Interestingly, s390x even has a hotplug notifier for that >> >> arch/s390/kernel/setup.c:kdump_mem_notifier() >> >> (offlining of memory on s390x can result in memory getting depopulated >> in the hypervisor, so after it would have been offlined, it would no >> longer be accessible. I somewhat doubt that this notifier is really >> needed - all pages in the crashkernel area should look like ordinary >> allocated pages when the area is reserved early during boot via the >> memblock allocator, and therefore offlining cannot succeed. But that's a >> different story - and I suspect this is a leftover from pre-memblock tim= es.) >=20 > It might be worth seeing if that is true, or if we need to generalize the > s390x code. I'll try to find some time to test if the s390x handler is still relevant. --=20 Thanks, David / dhildenb