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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3A408C00140 for ; Wed, 24 Aug 2022 10:43:43 +0000 (UTC) Received: from localhost ([::1]:47972 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oQnrK-0006Zx-BK for qemu-devel@archiver.kernel.org; Wed, 24 Aug 2022 06:43:42 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45254) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oQmyG-00081y-O5 for qemu-devel@nongnu.org; Wed, 24 Aug 2022 05:46:50 -0400 Received: from mga02.intel.com ([134.134.136.20]:36038) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oQmyE-0002aF-6c for qemu-devel@nongnu.org; Wed, 24 Aug 2022 05:46:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1661334406; x=1692870406; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:in-reply-to; bh=8HINI0FFOmHZ98p+KrUxRjOuWiCSe4IMz6bvZat9QRk=; b=TFCKUHDmP7spFLL65TJaYRg2KBql3OdV+VwyM3punwRDeT6o3C7btE8b Hhut6h4UonulqTVp2JYIC0PfyChZAIAhCebTkPkWf20YkDU8jpj1s3qyv KI2kHbVOVCb72g4Xre+haIkLf/Uqv/9MXsi7+u4WEaTo/JlKewaHyE5fQ NwhNJpyOb8HlIL36goPmDWGgrYz2u3ZiZJ5Txzrsh3NMpoFpVmUL7nHJi lDhhWFVTZQVRXXTZKLVWEaCVTdPhkckX3/mlKyIrgFGAWVyj9jFYY3H6R siCPruY45Qrp3HX1Yrecat5TJwUOHJI81MHxMFGWxtr9A0v3X9K2LuAWx A==; X-IronPort-AV: E=McAfee;i="6500,9779,10448"; a="280895659" X-IronPort-AV: E=Sophos;i="5.93,260,1654585200"; d="scan'208";a="280895659" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Aug 2022 02:46:43 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.93,260,1654585200"; d="scan'208";a="605977030" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.193.75]) by orsmga007.jf.intel.com with ESMTP; 24 Aug 2022 02:46:32 -0700 Date: Wed, 24 Aug 2022 17:41:49 +0800 From: Chao Peng To: Sean Christopherson Cc: David Hildenbrand , Hugh Dickins , "Kirill A . Shutemov" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org, linux-kselftest@vger.kernel.org, Paolo Bonzini , Jonathan Corbet , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com, Muchun Song , "Gupta, Pankaj" Subject: Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory Message-ID: <20220824094149.GA1383966@chaop.bj.intel.com> References: <20220706082016.2603916-1-chao.p.peng@linux.intel.com> <20220818132421.6xmjqduempmxnnu2@box> <226ab26d-9aa8-dce2-c7f0-9e3f5b65b63@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Received-SPF: none client-ip=134.134.136.20; envelope-from=chao.p.peng@linux.intel.com; helo=mga02.intel.com X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Chao Peng Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Aug 23, 2022 at 04:05:27PM +0000, Sean Christopherson wrote: > On Tue, Aug 23, 2022, David Hildenbrand wrote: > > On 19.08.22 05:38, Hugh Dickins wrote: > > > On Fri, 19 Aug 2022, Sean Christopherson wrote: > > >> On Thu, Aug 18, 2022, Kirill A . Shutemov wrote: > > >>> On Wed, Aug 17, 2022 at 10:40:12PM -0700, Hugh Dickins wrote: > > >>>> On Wed, 6 Jul 2022, Chao Peng wrote: > > >>>> But since then, TDX in particular has forced an effort into preventing > > >>>> (by flags, seals, notifiers) almost everything that makes it shmem/tmpfs. > > >>>> > > >>>> Are any of the shmem.c mods useful to existing users of shmem.c? No. > > >>>> Is MFD_INACCESSIBLE useful or comprehensible to memfd_create() users? No. > > >> > > >> But QEMU and other VMMs are users of shmem and memfd. The new features certainly > > >> aren't useful for _all_ existing users, but I don't think it's fair to say that > > >> they're not useful for _any_ existing users. > > > > > > Okay, I stand corrected: there exist some users of memfd_create() > > > who will also have use for "INACCESSIBLE" memory. > > > > As raised in reply to the relevant patch, I'm not sure if we really have > > to/want to expose MFD_INACCESSIBLE to user space. I feel like this is a > > requirement of specific memfd_notifer (memfile_notifier) implementations > > -- such as TDX that will convert the memory and MCE-kill the machine on > > ordinary write access. We might be able to set/enforce this when > > registering a notifier internally instead, and fail notifier > > registration if a condition isn't met (e.g., existing mmap). > > > > So I'd be curious, which other users of shmem/memfd would benefit from > > (MMU)-"INACCESSIBLE" memory obtained via memfd_create()? > > I agree that there's no need to expose the inaccessible behavior via uAPI. Making > it a kernel-internal thing that's negotiated/resolved when KVM binds to the fd > would align INACCESSIBLE with the UNMOVABLE and UNRECLAIMABLE flags (and any other > flags that get added in the future). > > AFAICT, the user-visible flag is a holdover from the early RFCs and doesn't provide > any unique functionality. That's also what I'm thinking. And I don't see problem immediately if user has populated the fd at the binding time. Actually that looks an advantage for previously discussed guest payload pre-loading. > > If we go that route, we might want to have shmem/memfd require INACCESSIBLE to be > set for the initial implementation. I.e. disallow binding without INACCESSIBLE > until there's a use case. I can do that. Chao