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 6FAA3C55185 for ; Wed, 22 Apr 2020 16:40:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EB28021569 for ; Wed, 22 Apr 2020 16:40:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Ct0k0Jrm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB28021569 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 603398E0011; Wed, 22 Apr 2020 12:40:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5B4AF8E0003; Wed, 22 Apr 2020 12:40:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4A33B8E0011; Wed, 22 Apr 2020 12:40:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0176.hostedemail.com [216.40.44.176]) by kanga.kvack.org (Postfix) with ESMTP id 330BA8E0003 for ; Wed, 22 Apr 2020 12:40:30 -0400 (EDT) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E36585008 for ; Wed, 22 Apr 2020 16:40:29 +0000 (UTC) X-FDA: 76736054178.27.dress93_5b9a0e2686e2c X-HE-Tag: dress93_5b9a0e2686e2c X-Filterd-Recvd-Size: 8047 Received: from us-smtp-delivery-1.mimecast.com (us-smtp-2.mimecast.com [207.211.31.81]) by imf33.hostedemail.com (Postfix) with ESMTP for ; Wed, 22 Apr 2020 16:40:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587573628; 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=O8dHC9tIPnlBcOmhl3RdZyYoyltFLHCpw21qAs5lDYI=; b=Ct0k0JrmmQLNcqKibrjIqxbkbY+qxzb+E2gMaW9PoDVcjr5jOIk0qCL6QVGRcU6Z/QfC6J 3fJQ4VC+KqvU+gG2PReCnGXiFoQ9EJ9pg3MFkp1lqPS2vCUuu6XfiPiPdefdJToYZjzgS2 N2S2PYUGTWph6Tvty2c3PvVz9eVoQRU= 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-431-o5L3ZBzmP_qCY7qnAZTpyA-1; Wed, 22 Apr 2020 12:40:27 -0400 X-MC-Unique: o5L3ZBzmP_qCY7qnAZTpyA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A2A571800D6B; Wed, 22 Apr 2020 16:40:25 +0000 (UTC) Received: from [10.36.114.57] (ovpn-114-57.ams2.redhat.com [10.36.114.57]) by smtp.corp.redhat.com (Postfix) with ESMTP id 81BC55D9E2; Wed, 22 Apr 2020 16:40:23 +0000 (UTC) Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image To: "Eric W. Biederman" , James Morse Cc: 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> 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: Wed, 22 Apr 2020 18:40:22 +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: <87y2qn1r18.fsf@x220.int.ebiederm.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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: > The confusing part was talking about memory being still in use, > that is actually scheduled for use in the future. +1 >=20 >>> 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? [...] >>> 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. >=20 > The design is: > =09sys_kexec_load() > =09shutdown scripts > sys_reboot(LINUX_REBOOT_CMD_KEXEC); >=20 > 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. >=20 > 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 removed. 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 times.= ) --=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,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 0BCD6C54FCB for ; Wed, 22 Apr 2020 16:40:41 +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 D29DE214AF for ; Wed, 22 Apr 2020 16:40:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="i9L6zssZ"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Ct0k0Jrm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D29DE214AF 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=PCpu95fOh1SV2N0pu2SrkhzuBukui29dhd4bnsE38mQ=; b=i9L6zssZBV8MIS MrTfBPaRpkCAkxgIFQdIih2DWSYxye0/xaUg+k9hCJ81IzoEdXVtXshRKXr50IKHeNLaGNcV2X/CJ 1UJ+58KxjKL75kGfldJWzoJJljLVHnmgxlFR5l48dTuo9gyLbPaYcR+rapDEvLYAb5ddAdZ4nCF0E YNFTliG4PnIZhc/zKSDzWzX6ORsVTrlTjbtptSxYjxR8rb51tmAJHcrtCA62WeqFthDlCzF6kSF6z YKLhZ3sGueXWWawOSOVmBrkbNAbisbV0/6vHIqHzG+TINQERER1NgibtEh8ymBbabB7eFAC9EAJ4g i+D04vgEHRydQjJ0f9lQ==; 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 1jRIQO-0006ZD-44; Wed, 22 Apr 2020 16:40:36 +0000 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120] helo=us-smtp-1.mimecast.com) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jRIQJ-0006V7-JC for linux-arm-kernel@lists.infradead.org; Wed, 22 Apr 2020 16:40:33 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587573628; 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=O8dHC9tIPnlBcOmhl3RdZyYoyltFLHCpw21qAs5lDYI=; b=Ct0k0JrmmQLNcqKibrjIqxbkbY+qxzb+E2gMaW9PoDVcjr5jOIk0qCL6QVGRcU6Z/QfC6J 3fJQ4VC+KqvU+gG2PReCnGXiFoQ9EJ9pg3MFkp1lqPS2vCUuu6XfiPiPdefdJToYZjzgS2 N2S2PYUGTWph6Tvty2c3PvVz9eVoQRU= 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-431-o5L3ZBzmP_qCY7qnAZTpyA-1; Wed, 22 Apr 2020 12:40:27 -0400 X-MC-Unique: o5L3ZBzmP_qCY7qnAZTpyA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A2A571800D6B; Wed, 22 Apr 2020 16:40:25 +0000 (UTC) Received: from [10.36.114.57] (ovpn-114-57.ams2.redhat.com [10.36.114.57]) by smtp.corp.redhat.com (Postfix) with ESMTP id 81BC55D9E2; Wed, 22 Apr 2020 16:40:23 +0000 (UTC) Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image To: "Eric W. Biederman" , James Morse 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> 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: Wed, 22 Apr 2020 18:40:22 +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: <87y2qn1r18.fsf@x220.int.ebiederm.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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-20200422_094031_722196_B26B2F38 X-CRM114-Status: GOOD ( 17.33 ) 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, linux-mm@kvack.org, 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 > 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? [...] >>> 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: > sys_kexec_load() > shutdown 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 removed. 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 times.) -- 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-delivery-1.mimecast.com ([207.211.31.120] helo=us-smtp-1.mimecast.com) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jRIQJ-0006VU-P5 for kexec@lists.infradead.org; Wed, 22 Apr 2020 16:40:33 +0000 Subject: Re: [PATCH 1/3] kexec: Prevent removal of memory in use by a loaded kexec image 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> From: David Hildenbrand Message-ID: Date: Wed, 22 Apr 2020 18:40:22 +0200 MIME-Version: 1.0 In-Reply-To: <87y2qn1r18.fsf@x220.int.ebiederm.org> 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: "Eric W. Biederman" , James Morse Cc: Anshuman Khandual , Catalin Marinas , Bhupesh Sharma , kexec@lists.infradead.org, linux-mm@kvack.org, Andrew Morton , Will Deacon , linux-arm-kernel@lists.infradead.org > 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? [...] >>> 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: > sys_kexec_load() > shutdown 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 removed. 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 times.) -- Thanks, David / dhildenb _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec