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=-5.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,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 2422BC2D0A3 for ; Tue, 3 Nov 2020 10:12:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BEBA6206F8 for ; Tue, 3 Nov 2020 10:12:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="GNa/9Cyg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726211AbgKCKMM (ORCPT ); Tue, 3 Nov 2020 05:12:12 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:26121 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726312AbgKCKML (ORCPT ); Tue, 3 Nov 2020 05:12:11 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604398329; 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; bh=OyipNVQSi+6EWMMakyEP0aw5V3oxIqNV8RP/zduqoUw=; b=GNa/9Cygvl4mUZcGn7V7OtWZ6w8d4PuD4m+FHGDrOVFBMKqurcOe9YTmT0AQ+yZNSJjHk3 Vra/tNN+2dbcnohmTsjObAJiPL40+W45ireLES3gNXRyBu5KSfPCWAdaigxIEP5m5hQSWO lmbviLNsQlNizkBtTFZ/0RqbcYir2mY= 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-270-LbFmUSJyMSGOd-g7tICDgg-1; Tue, 03 Nov 2020 05:12:05 -0500 X-MC-Unique: LbFmUSJyMSGOd-g7tICDgg-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 5B23E186840C; Tue, 3 Nov 2020 10:12:00 +0000 (UTC) Received: from [10.36.115.7] (ovpn-115-7.ams2.redhat.com [10.36.115.7]) by smtp.corp.redhat.com (Postfix) with ESMTP id 771815D9CC; Tue, 3 Nov 2020 10:11:52 +0000 (UTC) Subject: Re: [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas To: Mike Rapoport Cc: Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Idan Yaniv , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , Thomas Gleixner , Shuah Khan , Tycho Andersen , Will Deacon , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org References: <20200924132904.1391-1-rppt@kernel.org> <9c38ac3b-c677-6a87-ce82-ec53b69eaf71@redhat.com> <20201102174308.GF4879@kernel.org> <20201103095247.GH4879@kernel.org> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <5709dadf-81c6-5b40-93d4-fbef94d5aad8@redhat.com> Date: Tue, 3 Nov 2020 11:11:51 +0100 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: <20201103095247.GH4879@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 03.11.20 10:52, Mike Rapoport wrote: > On Mon, Nov 02, 2020 at 06:51:09PM +0100, David Hildenbrand wrote: >>>> Assume you have a system with quite some ZONE_MOVABLE memory (esp. in >>>> virtualized environments), eating up a significant amount of !ZONE_MOVABLE >>>> memory dynamically at runtime can lead to non-obvious issues. It looks like >>>> you have plenty of free memory, but the kernel might still OOM when trying >>>> to do kernel allocations e.g., for pagetables. With CMA we at least know >>>> what we're dealing with - it behaves like ZONE_MOVABLE except for the owner >>>> that can place unmovable pages there. We can use it to compute statically >>>> the amount of ZONE_MOVABLE memory we can have in the system without doing >>>> harm to the system. >>> >>> Why would you say that secretmem allocates from !ZONE_MOVABLE? >>> If we put boot time reservations aside, the memory allocation for >>> secretmem follows the same rules as the memory allocations for any file >>> descriptor. That means we allocate memory with GFP_HIGHUSER_MOVABLE. >> >> Oh, okay - I missed that! I had the impression that pages are unmovable and >> allocating from ZONE_MOVABLE would be a violation of that? >> >>> After the allocation the memory indeed becomes unmovable but it's not >>> like we are eating memory from other zones here. >> >> ... and here you have your problem. That's a no-no. We only allow it in very >> special cases where it can't be avoided - e.g., vfio having to pin guest >> memory when passing through memory to VMs. >> >> Hotplug memory, online it to ZONE_MOVABLE. Allocate secretmem. Try to unplug >> the memory again -> endless loop in offline_pages(). >> >> Or have a CMA area that gets used with GFP_HIGHUSER_MOVABLE. Allocate >> secretmem. The owner of the area tries to allocate memory - always fails. >> Purpose of CMA destroyed. >> >>> >>>> Ideally, we would want to support page migration/compaction and allow for >>>> allocation from ZONE_MOVABLE as well. Would involve temporarily mapping, >>>> copying, unmapping. Sounds feasible, but not sure which roadblocks we would >>>> find on the way. >>> >>> We can support migration/compaction with temporary mapping. The first >>> roadblock I've hit there was that migration allocates 4K destination >>> page and if we use it in secret map we are back to scrambling the direct >>> map into 4K pieces. It still sounds feasible but not as trivial :) >> >> That sounds like the proper way for me to do it then. > > Although migration of secretmem pages sounds feasible now, there maybe > other issues I didn't see because I'm not very familiar with > migration/compaction code. Migration of PMDs might also be feasible - and it would be even cleaner. But I agree that that might require more work and starting with something simpler (!movable) is the right way to move forward. -- Thanks, David / dhildenb