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=-6.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 0C32FC433DB for ; Thu, 11 Feb 2021 23:10:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A684564E05 for ; Thu, 11 Feb 2021 23:10:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229501AbhBKXKa (ORCPT ); Thu, 11 Feb 2021 18:10:30 -0500 Received: from mail.kernel.org ([198.145.29.99]:47506 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229564AbhBKXKO (ORCPT ); Thu, 11 Feb 2021 18:10:14 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id F14AF64DF3; Thu, 11 Feb 2021 23:09:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1613084973; bh=5lHiqnqqzqNi5/OSSDr9bdxtAGi+3a9C3En/9Cfu+Ss=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KdQTRQFGFCn97Jxdu/WPirdvPSClIiQe3eCuboHTtWi+7E6/HzcS9qnWDJfg5uDFN ZY5PuEAEMXaKZcGprf7SdyWk9I93Lln3hFbxMp/KrXIzze9mx092L3Jh7i5UxEbimS cejoByXzKhnjLnxouWOf/ewU3WweBYFzmyuAwZ+NBMVNgyCt3ntX2Xw6TB28PoSs4H mwoZV1kJ8Ervt9UJn0zr12hQYhd+uIYZ9COxTA7mUSvHvGQIa7oorM8qITwmhhkYJK xRQGEMhSjFJwWRNKbKOuAa8QLAh9zI5u11sQAct0mWsv9haX/Z+R9q39gWv4lXPETF dH+b9ZCWAtkuQ== Date: Fri, 12 Feb 2021 01:09:10 +0200 From: Mike Rapoport To: David Hildenbrand Cc: Michal Hocko , 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 Subject: Re: [PATCH v17 07/10] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <20210211230910.GL242749@kernel.org> References: <20210208212605.GX242749@kernel.org> <20210209090938.GP299309@linux.ibm.com> <20210211071319.GF242749@kernel.org> <0d66baec-1898-987b-7eaf-68a015c027ff@redhat.com> <20210211112702.GI242749@kernel.org> <05082284-bd85-579f-2b3e-9b1af663eb6f@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <05082284-bd85-579f-2b3e-9b1af663eb6f@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 11, 2021 at 01:07:10PM +0100, David Hildenbrand wrote: > On 11.02.21 12:27, Mike Rapoport wrote: > > On Thu, Feb 11, 2021 at 10:01:32AM +0100, David Hildenbrand wrote: > > So let's talk about the main user-visible differences to other memfd files > (especially, other purely virtual files like hugetlbfs). With secretmem: > > - File content can only be read/written via memory mappings. > - File content cannot be swapped out. > > I think there are still valid ways to modify file content using syscalls: > e.g., fallocate(PUNCH_HOLE). Things like truncate also seems to work just > fine. These work perfectly with any file, so maybe we should have added memfd_create as a flag to open(2) back then and now the secretmem file descriptors? > > > AFAIKS, we would need MFD_SECRET and disallow > > > MFD_ALLOW_SEALING and MFD_HUGETLB. > > > > So here we start to multiplex. > > Yes. And as Michal said, maybe we can support combinations in the future. Isn't there a general agreement that syscall multiplexing is not a good thing? memfd_create already has flags validation that does not look very nice. Adding there only MFD_SECRET will make it a bit less nice, but when we'll grow new functionality into secretmem that will become horrible. -- Sincerely yours, Mike.