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=-5.2 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 74386C433E0 for ; Thu, 11 Feb 2021 10:02:30 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0237F64EAA for ; Thu, 11 Feb 2021 10:02:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0237F64EAA 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 5BAD56B00AA; Thu, 11 Feb 2021 05:02:29 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 5696D6B00AB; Thu, 11 Feb 2021 05:02:29 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3E2266B00AC; Thu, 11 Feb 2021 05:02:29 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0128.hostedemail.com [216.40.44.128]) by kanga.kvack.org (Postfix) with ESMTP id 1CE3F6B00AA for ; Thu, 11 Feb 2021 05:02:29 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id D6FFC6C36 for ; Thu, 11 Feb 2021 10:02:28 +0000 (UTC) X-FDA: 77805547176.12.boat83_61133a827617 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id B5FEF18001FA8 for ; Thu, 11 Feb 2021 10:02:28 +0000 (UTC) X-HE-Tag: boat83_61133a827617 X-Filterd-Recvd-Size: 6291 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [63.128.21.124]) by imf21.hostedemail.com (Postfix) with ESMTP for ; Thu, 11 Feb 2021 10:02:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613037747; 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=HvJ6ODrJsIAiBu7p562Cs80l2ihUXPDYjoFL2LYVwNg=; b=c5bsa43y5sQynpuLaf58W8udP9TioovbETtznXBYnDpqOo7vbUhqusFFm1LoANvMehc4Gw 1Y1etWtFBtVWQg853mc3msBQSMLulVOxUn0OQ3Re/yguwxptZcVcW48gILtkNtDjvHfYlr J1OMQrbL5c4ofJFAuXAt4PbQwJdAXTk= 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-412-xjh0NtfMOp6y4PYLBjaekA-1; Thu, 11 Feb 2021 05:02:23 -0500 X-MC-Unique: xjh0NtfMOp6y4PYLBjaekA-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 79EADC73A0; Thu, 11 Feb 2021 10:02:18 +0000 (UTC) Received: from [10.36.114.52] (ovpn-114-52.ams2.redhat.com [10.36.114.52]) by smtp.corp.redhat.com (Postfix) with ESMTP id D2B4F5D9E8; Thu, 11 Feb 2021 10:02:08 +0000 (UTC) To: 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 , James Bottomley , "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: <20210208084920.2884-1-rppt@kernel.org> <20210208084920.2884-8-rppt@kernel.org> <20210208212605.GX242749@kernel.org> <20210209090938.GP299309@linux.ibm.com> <20210211071319.GF242749@kernel.org> <0d66baec-1898-987b-7eaf-68a015c027ff@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH v17 07/10] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: Date: Thu, 11 Feb 2021 11:02:07 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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 11.02.21 10:38, Michal Hocko wrote: > On Thu 11-02-21 10:01:32, David Hildenbrand wrote: > [...] >> AFAIKS, we would need MFD_SECRET and disallow >> MFD_ALLOW_SEALING and MFD_HUGETLB. >=20 > Yes for an initial version. But I do expect a request to support both > features is just a matter of time. >=20 >> In addition, we could add MFD_SECRET_NEVER_MAP, which could disallow a= ny kind of >> temporary mappings (eor migration). TBC. >=20 > I believe this is the mode Mike wants to have by default. A more relax > one would be an opt-in. MFD_SECRET_RELAXED which would allow temporal > mappings in the kernel for content copying (e.g. for migration). >=20 >> --- >> >> Some random thoughts regarding files. >> >> What is the page size of secretmem memory? Sometimes we use huge pages= , >> sometimes we fallback to 4k pages. So I assume huge pages in general? >=20 > Unless there is an explicit request for hugetlb I would say the page > size is not really important like for any other fds. Huge pages can be > used transparently. > =20 >> What are semantics of MADV()/FALLOCATE() etc on such files? >=20 > I would expect the same semantic as regular shmem (memfd_create) except > the memory doesn't have _any_ backing storage which makes it > unevictable. So the reclaim related madv won't work but there shouldn't > be any real reason why e.g. MADV_DONTNEED, WILLNEED, DONT_FORK and > others don't work. Another thought regarding "doesn't have _any_ backing storage" What are the right semantics when it comes to memory accounting/commit? As secretmem does not have a) any backing storage b) cannot go to swap The MAP_NORESERVE vs. !MAP_NORESERVE handling gets a little unclear. Why=20 "reserve swap space" if the allocations cannot ever go to swap? Sure, we=20 want to "reserve physical memory", but in contrast to other users that=20 can go to swap. Of course, this is only relevant for MAP_PRIVATE secretmem mappings.=20 Other MAP_SHARED assumes there is no need for reserving swap space as it=20 can just go to the backing storage. (yeah, tmpfs/shmem is weird in that=20 regard as well, but again, it's a bit different) --=20 Thanks, David / dhildenb