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 BB7EEC433E0 for ; Thu, 11 Feb 2021 09:49:10 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4111164E9C for ; Thu, 11 Feb 2021 09:49:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4111164E9C 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 8250E6B00A6; Thu, 11 Feb 2021 04:49:09 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7D5B16B00A7; Thu, 11 Feb 2021 04:49:09 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 69D536B00A8; Thu, 11 Feb 2021 04:49:09 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0211.hostedemail.com [216.40.44.211]) by kanga.kvack.org (Postfix) with ESMTP id 55D186B00A6 for ; Thu, 11 Feb 2021 04:49:09 -0500 (EST) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 0425183FD for ; Thu, 11 Feb 2021 09:49:09 +0000 (UTC) X-FDA: 77805513618.21.burst38_0508aa927617 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id D6571180442C0 for ; Thu, 11 Feb 2021 09:49:08 +0000 (UTC) X-HE-Tag: burst38_0508aa927617 X-Filterd-Recvd-Size: 6184 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf25.hostedemail.com (Postfix) with ESMTP for ; Thu, 11 Feb 2021 09:49:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613036947; 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=D4KClAbW7qAjd5KF/8/23pSoF5vXBE09nxYc8TlmEUM=; b=Wvdx4T0etpdPbxWRf+PxEFJXyobCquw7Ia8NzvSSWzmUeffoQFWCwdClzG+m2Hkk8SGnwz YemrIMC0OdkIuCDMBpWRJZLYEyOEpk0bZYvgjNDOCVi2cH9z7BygdvvfF0ff+TP6/Zp8DF XksTP0UZovQLIQrBYO+RF7TlE+rTDvQ= 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-249-9tsn6XZgPY-p0wHYN_-nmw-1; Thu, 11 Feb 2021 04:49:03 -0500 X-MC-Unique: 9tsn6XZgPY-p0wHYN_-nmw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6F49280364D; Thu, 11 Feb 2021 09:48:58 +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 4AE5010016F4; Thu, 11 Feb 2021 09:48:49 +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: <367808fc-8f5c-10a4-fc0b-a71df616dfce@redhat.com> Date: Thu, 11 Feb 2021 10:48:48 +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 2.84 on 10.5.11.22 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: >> 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. If everything is currently allocated/mapped on PTE granularity, then yes=20 I agree. I remember previous versions used to "pool 2MB pages", which=20 might have been problematic (thus, my concerns regarding mmap() etc.).=20 If that part is now gone, good! > =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. Agreed if we don't have hugepage semantics. >> Is userfaultfd() properly fenced? Or does it even work (doubt)? >> >> How does it behave if I mmap(FIXED) something in between? >> In which granularity can I do that (->page-size?)? >=20 > Again, nothing really exceptional here. This is a mapping like any > other from address space manipulation POV. Agreed with the PTE mapping approach. >=20 >> What are other granularity restrictions (->page size)? >> >> Don't want to open a big discussion here, just some random thoughts. >> Maybe it has all been already figured out and most of the answers >> above are "Fails with -EINVAL". >=20 > I think that the behavior should be really in sync with shmem semantic > as much as possible. Most operations should simply work with an > aditional direct map manipulation. There is no real reason to be > special. Some functionality might be missing, e.g. hugetlb support but > that has been traditionally added on top of shmem interface so nothing > really new here. Agreed! --=20 Thanks, David / dhildenb