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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 D1A7CC433E6 for ; Tue, 9 Feb 2021 08:50:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9560164E54 for ; Tue, 9 Feb 2021 08:50:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230124AbhBIIuF (ORCPT ); Tue, 9 Feb 2021 03:50:05 -0500 Received: from mx2.suse.de ([195.135.220.15]:56736 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230201AbhBIIr6 (ORCPT ); Tue, 9 Feb 2021 03:47:58 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1612860431; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=7uXNoYTwJcul85Ggr79faNz9sm4xUBP5tyQrp7MGBDU=; b=igFK6y52//YbOeER2qu6o8xC111AEEf/9O0tsPnCXBARwevxGar35/sufXf6VC6tmzQnyW /X0B3+BhzxxFnhgpH7/ijVkSsmiVTBYgLKz7SupOE55ZHrLDJUiANJxkyr5fgautM81txk U8MaQSKu/ApzxONYDBE500FYqjbKj30= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7514CAB71; Tue, 9 Feb 2021 08:47:11 +0000 (UTC) Date: Tue, 9 Feb 2021 09:47:08 +0100 From: Michal Hocko To: Mike Rapoport Cc: Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , David Hildenbrand , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Mike Rapoport , 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: References: <20210208084920.2884-1-rppt@kernel.org> <20210208084920.2884-8-rppt@kernel.org> <20210208212605.GX242749@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210208212605.GX242749@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Mon 08-02-21 23:26:05, Mike Rapoport wrote: > On Mon, Feb 08, 2021 at 11:49:22AM +0100, Michal Hocko wrote: > > On Mon 08-02-21 10:49:17, Mike Rapoport wrote: [...] > > > The file descriptor based memory has several advantages over the > > > "traditional" mm interfaces, such as mlock(), mprotect(), madvise(). It > > > paves the way for VMMs to remove the secret memory range from the process; > > > > I do not understand how it helps to remove the memory from the process > > as the interface explicitly allows to add a memory that is removed from > > all other processes via direct map. > > The current implementation does not help to remove the memory from the > process, but using fd-backed memory seems a better interface to remove > guest memory from host mappings than mmap. As Andy nicely put it: > > "Getting fd-backed memory into a guest will take some possibly major work in > the kernel, but getting vma-backed memory into a guest without mapping it > in the host user address space seems much, much worse." OK, so IIUC this means that the model is to hand over memory from host to guest. I thought the guest would be under control of its address space and therefore it operates on the VMAs. This would benefit from an additional and more specific clarification. > > > As secret memory implementation is not an extension of tmpfs or hugetlbfs, > > > usage of a dedicated system call rather than hooking new functionality into > > > memfd_create(2) emphasises that memfd_secret(2) has different semantics and > > > allows better upwards compatibility. > > > > What is this supposed to mean? What are differences? > > Well, the phrasing could be better indeed. That supposed to mean that > they differ in the semantics behind the file descriptor: memfd_create > implements sealing for shmem and hugetlbfs while memfd_secret implements > memory hidden from the kernel. Right but why memfd_create model is not sufficient for the usecase? Please note that I am arguing against. To be honest I do not really care much. Using an existing scheme is usually preferable from my POV but there might be real reasons why shmem as a backing "storage" is not appropriate. > > > The secretmem mappings are locked in memory so they cannot exceed > > > RLIMIT_MEMLOCK. Since these mappings are already locked an attempt to > > > mlock() secretmem range would fail and mlockall() will ignore secretmem > > > mappings. > > > > What about munlock? > > Isn't this implied? ;-) My bad here. I thought that munlock fails on vmas which are not mlocked and I was curious about the behavior when mlockall() is followed by munlock. But I do not see this being the case. So this should be ok. -- Michal Hocko SUSE Labs