From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=37L1=HY=lists.01.org=linux-nvdimm-bounces@kernel.org>
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=-5.0 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,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 B70A6C433E0
	for <linux-nvdimm@archiver.kernel.org>; Mon, 22 Feb 2021 10:50:24 +0000 (UTC)
Received: from ml01.01.org (ml01.01.org [198.145.21.10])
	(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 4EF5B64E41
	for <linux-nvdimm@archiver.kernel.org>; Mon, 22 Feb 2021 10:50:24 +0000 (UTC)
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4EF5B64E41
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-nvdimm-bounces@lists.01.org
Received: from ml01.vlan13.01.org (localhost [IPv6:::1])
	by ml01.01.org (Postfix) with ESMTP id 2438E100EBB78;
	Mon, 22 Feb 2021 02:50:24 -0800 (PST)
Received-SPF: Pass (mailfrom) identity=mailfrom; client-ip=216.205.24.124; helo=us-smtp-delivery-124.mimecast.com; envelope-from=david@redhat.com; receiver=<UNKNOWN> 
Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits))
	(No client certificate requested)
	by ml01.01.org (Postfix) with ESMTPS id 51FBF100EC1C8
	for <linux-nvdimm@lists.01.org>; Mon, 22 Feb 2021 02:50:20 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;
	s=mimecast20190719; t=1613991019;
	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=AX6S5jlyFuflTUx2zqx5z6yBrSd2+MnM/4YhHnjFCrVfzIP8/WwEg9xHCE5gqsJLkj/ROD
	60DCOlE36abjUd0ElRxQpoVh8IWnzi5RCsITce0UKEoqOsuRWzzSX9oqrhN9VXQxZHVUkp
	Cq0Trf72niZeIWV9ZOjfCVT0NZYG7T0=
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 <david@redhat.com>
To: jejb@linux.ibm.com, Michal Hocko <mhocko@suse.com>
References: <20210214091954.GM242749@kernel.org>
 <052DACE9-986B-424C-AF8E-D6A4277DE635@redhat.com>
 <244f86cba227fa49ca30cd595c4e5538fe2f7c2b.camel@linux.ibm.com>
 <YCo7TqUnBdgJGkwN@dhcp22.suse.cz>
 <be1d821d3f0aec24ad13ca7126b4359822212eb0.camel@linux.ibm.com>
 <YCrJjYmr7A2nO6lA@dhcp22.suse.cz>
 <12c3890b233c8ec8e3967352001a7b72a8e0bfd0.camel@linux.ibm.com>
 <dfd7db5c-a8c7-0676-59f8-70aa6bcaabe7@redhat.com>
 <000cfaa0a9a09f07c5e50e573393cda301d650c9.camel@linux.ibm.com>
 <5a8567a9-6940-c23f-0927-e4b5c5db0d5e@redhat.com>
 <b58debfe598331791ecc238a6bf8d2cf1762203a.camel@linux.ibm.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-Language: en-US
X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13
Message-ID-Hash: HBUYJA4RFIXYVGRSP6WXQ6CPVUL2CBBC
X-Message-ID-Hash: HBUYJA4RFIXYVGRSP6WXQ6CPVUL2CBBC
X-MailFrom: david@redhat.com
X-Mailman-Rule-Hits: nonmember-moderation
X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation
CC: Mike Rapoport <rppt@kernel.org>, Mike Rapoport <rppt@linux.ibm.com>, Andrew Morton <akpm@linux-foundation.org>, Alexander Viro <viro@zeniv.linux.org.uk>, Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>, Catalin Marinas <catalin.marinas@arm.com>, Christopher Lameter <cl@linux.com>, Dave Hansen <dave.hansen@linux.intel.com>, Elena Reshetova <elena.reshetova@intel.com>, "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>, "Kirill A. Shutemov" <kirill@shutemov.name>, Matthew Wilcox <willy@infradead.org>, Mark Rutland <mark.rutland@arm.com>, Michael Kerrisk <mtk.manpages@gmail.com>, Palmer Dabbelt <palmer@dabbelt.com>, Paul Walmsley <paul.walmsley@sifive.com>, Peter Zijlstra <peterz@infradead.org>, Rick Edgecombe <rick.p.edgecombe@intel.com>, Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>, Shuah Khan <shuah@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Tycho Andersen <tycho@tycho.ws>, Will Deacon <wil
 l@kernel.org>, 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 <hagen@jauu.net>, Palmer Dabbelt <palmerdabbelt@google.com>
X-Mailman-Version: 3.1.1
Precedence: list
List-Id: "Linux-nvdimm developer list." <linux-nvdimm.lists.01.org>
Archived-At: <https://lists.01.org/hyperkitty/list/linux-nvdimm@lists.01.org/message/HBUYJA4RFIXYVGRSP6WXQ6CPVUL2CBBC/>
List-Archive: <https://lists.01.org/hyperkitty/list/linux-nvdimm@lists.01.org/>
List-Help: <mailto:linux-nvdimm-request@lists.01.org?subject=help>
List-Post: <mailto:linux-nvdimm@lists.01.org>
List-Subscribe: <mailto:linux-nvdimm-join@lists.01.org>
List-Unsubscribe: <mailto:linux-nvdimm-leave@lists.01.org>
Content-Type: text/plain; charset="us-ascii"; format="flowed"
Content-Transfer-Encoding: 7bit

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 failure
>> (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.
> 
> Sorry for the late reply, there is just too much going on :)
> 
> *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.
> 
> Until then, going with memfd_create() works just fine IMHO.
> 
> The worst think that could happen is that we might not be able to create
> 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.
> 

Adding to that, I'll give up arguing now as I have more important things 
to do. It has been questioned by various people why we need a dedicate 
syscall and at least for me, without a satisfying answer.

Worst thing is that we end up with a syscall that could have been 
avoided, for example, because
1. We add existing/future memfd_create() flags to memfd_secret() as well 
when we need them (sealing, hugetlb., ..).
2. We decide in the future to still add MFD_SECRET support to 
memfd_secret().

So be it.

-- 
Thanks,

David / dhildenb
_______________________________________________
Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org
To unsubscribe send an email to linux-nvdimm-leave@lists.01.org