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=-6.0 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 11F7AC433E9 for ; Sun, 14 Feb 2021 09:21:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E72D864E4E for ; Sun, 14 Feb 2021 09:21:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229768AbhBNJUy (ORCPT ); Sun, 14 Feb 2021 04:20:54 -0500 Received: from mail.kernel.org ([198.145.29.99]:46840 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229528AbhBNJUx (ORCPT ); Sun, 14 Feb 2021 04:20:53 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2CB2B64D73; Sun, 14 Feb 2021 09:19:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1613294412; bh=IojP/99cv2KZA0UAqkGIVvcnNQXpAQrGnDSYSmISYMk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ggTE3epmRlYiZpCIulQqzfZIZLk/o9Hy+eMY/vtIj4RBJvlbLU6YBe6xW+nn3Nh9o MyYMRX8NGusIKQSvjXjeNrYN2FzXGXOOYKN32wbF5K9UR5i2fL54NWoZ4kzch8O1fz 0j0N6t7YI6VhKfHIfT1MILdmaVlC+bJrUkGBAjCyOCyGfWtt4wmkaNl5ygGD55KRog FpJCiXGCmq9B5RiAfE9vA/ahNtHagvIeFYzLpSK837gPh4weRSFHUqNEb1+FAp4m0u 60OF5nZHG/kKqrkEsLohg2nOPziZfAIwq4U8bxWTmen5x/8iLmJMxF5gj8klmC/iDZ Da8cagTHmtKmw== Date: Sun, 14 Feb 2021 11:19:54 +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: <20210214091954.GM242749@kernel.org> References: <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> <20210211230910.GL242749@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Feb 12, 2021 at 10:18:19AM +0100, David Hildenbrand wrote: > On 12.02.21 00:09, Mike Rapoport wrote: > > 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? > > I think open() vs memfd_create() makes sense: for open, the path specifies > main properties (tmpfs, hugetlbfs, filesystem). On memfd, there is no such > path and the "type" has to be specified differently. > > Also, open() might open existing files - memfd always creates new files. Yes, but still open() returns a handle to a file and memfd_create() returns a handle to a file. The differences may be well hidden by e.g. O_MEMORY and than features unique to memfd files will have their set of O_SOMETHING flags. It's the same logic that says "we already have an interface that's close enough and it's fine to add a bunch of new flags there". And here we come to the question "what are the differences that justify a new system call?" and the answer to this is very subjective. And as such we can continue bikeshedding forever. -- Sincerely yours, Mike.