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=-5.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 7E27DC433DB for ; Mon, 22 Feb 2021 10:50:24 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1CD0E64E04 for ; Mon, 22 Feb 2021 10:50:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1CD0E64E04 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 7989A6B0006; Mon, 22 Feb 2021 05:50:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 722026B006C; Mon, 22 Feb 2021 05:50:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5C3E76B006E; Mon, 22 Feb 2021 05:50:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0042.hostedemail.com [216.40.44.42]) by kanga.kvack.org (Postfix) with ESMTP id 460806B0006 for ; Mon, 22 Feb 2021 05:50:23 -0500 (EST) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 025CD18016BDB for ; Mon, 22 Feb 2021 10:50:22 +0000 (UTC) X-FDA: 77845584726.18.232CC8E Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf07.hostedemail.com (Postfix) with ESMTP id D6160A0009D3 for ; Mon, 22 Feb 2021 10:50:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613991021; 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=B5Wwlru6GdzCo3Pp8y35Np82fHYLWpJqEicYWng65cw=; b=FdvkyOBmZeei7QJsFpH+WCZmLFOVd6LoIZY5GUKnc7ZOnIDanPNF3bPJksp96A3LTnZhMG 2Hr4YYlFDYQwwVyaDkONmEVs/rafO0bXPnvJ5OHitZBTzHzssHgORvDTaQnJ4rAuqSwBOV LzZUT7Jlq24YnYg2C4AlWC3WN3VeuGQ= 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-367-FssqEYNDO-izvW_G71aw3w-1; Mon, 22 Feb 2021 05:50:17 -0500 X-MC-Unique: FssqEYNDO-izvW_G71aw3w-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 37EEA100CC88; Mon, 22 Feb 2021 10:50:12 +0000 (UTC) Received: from [10.36.115.16] (ovpn-115-16.ams2.redhat.com [10.36.115.16]) by smtp.corp.redhat.com (Postfix) with ESMTP id 61DED7771A; Mon, 22 Feb 2021 10:50:03 +0000 (UTC) From: David Hildenbrand To: jejb@linux.ibm.com, Michal Hocko Cc: Mike Rapoport , Mike Rapoport , Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , 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, Hagen Paul Pfeifer , Palmer Dabbelt References: <20210214091954.GM242749@kernel.org> <052DACE9-986B-424C-AF8E-D6A4277DE635@redhat.com> <244f86cba227fa49ca30cd595c4e5538fe2f7c2b.camel@linux.ibm.com> <12c3890b233c8ec8e3967352001a7b72a8e0bfd0.camel@linux.ibm.com> <000cfaa0a9a09f07c5e50e573393cda301d650c9.camel@linux.ibm.com> <5a8567a9-6940-c23f-0927-e4b5c5db0d5e@redhat.com> <304e4c9d-81aa-20ac-cfbe-245ed0de9a86@redhat.com> Organization: Red Hat GmbH Subject: Re: [PATCH v17 07/10] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <878ca057-3262-179d-eb9b-a26829307d09@redhat.com> Date: Mon, 22 Feb 2021 11:50:02 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <304e4c9d-81aa-20ac-cfbe-245ed0de9a86@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Stat-Signature: qmfwkpr6nkf38rebp1kestfod1fmht5x X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D6160A0009D3 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf07; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1613991021-124902 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 22.02.21 10:38, David Hildenbrand wrote: > On 17.02.21 17:19, James Bottomley wrote: >> On Tue, 2021-02-16 at 18:16 +0100, David Hildenbrand wrote: >> [...] >>>>> The discussion regarding migratability only really popped up >>>>> because this is a user-visible thing and not being able to >>>>> migrate can be a real problem (fragmentation, ZONE_MOVABLE, ...). >>>> >>>> I think the biggest use will potentially come from hardware >>>> acceleration. If it becomes simple to add say encryption to a >>>> secret page with no cost, then no flag needed. However, if we only >>>> have a limited number of keys so once we run out no more encrypted >>>> memory then it becomes a costly resource and users might want a >>>> choice of being backed by encryption or not. >>> >>> Right. But wouldn't HW support with configurable keys etc. need more >>> syscall parameters (meaning, even memefd_secret() as it is would not >>> be sufficient?). I suspect the simplistic flag approach might not >>> be sufficient. I might be wrong because I have no clue about MKTME >>> and friends. >> >> The theory I was operating under is key management is automatic and >> hidden, but key scarcity can't be, so if you flag requesting hardware >> backing then you either get success (the kernel found a key) or failur= e >> (the kernel is out of keys). If we actually want to specify the key >> then we need an extra argument and we *must* have a new system call. >> >>> Anyhow, I still think extending memfd_create() might just be good >>> enough - at least for now. >> >> I really think this is the wrong approach for a user space ABI. If we >> think we'll ever need to move to a separate syscall, we should begin >> with one. The pain of trying to shift userspace from memfd_create to = a >> new syscall would be enormous. It's not impossible (see clone3) but >> it's a pain we should avoid if we know it's coming. >=20 > Sorry for the late reply, there is just too much going on :) >=20 > *If* we ever realize we need to pass more parameters we can easily have > a new syscall for that purpose. *Then*, we know how that syscall will > look like. Right now, it's just pure speculation. >=20 > Until then, going with memfd_create() works just fine IMHO. >=20 > The worst think that could happen is that we might not be able to creat= e > all fancy sectremem flavors in the future via memfd_create() but only > via different, highly specialized syscall. I don't see a real problem > with that. >=20 Adding to that, I'll give up arguing now as I have more important things=20 to do. It has been questioned by various people why we need a dedicate=20 syscall and at least for me, without a satisfying answer. Worst thing is that we end up with a syscall that could have been=20 avoided, for example, because 1. We add existing/future memfd_create() flags to memfd_secret() as well=20 when we need them (sealing, hugetlb., ..). 2. We decide in the future to still add MFD_SECRET support to=20 memfd_secret(). So be it. --=20 Thanks, David / dhildenb