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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 65C00C433FE for ; Mon, 17 Oct 2022 16:20:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229815AbiJQQUT (ORCPT ); Mon, 17 Oct 2022 12:20:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52738 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229675AbiJQQUP (ORCPT ); Mon, 17 Oct 2022 12:20:15 -0400 Received: from mga07.intel.com (mga07.intel.com [134.134.136.100]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA74B6C119; Mon, 17 Oct 2022 09:20:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1666023614; x=1697559614; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=K4vrfLL2l6+gAD4B8xJLdJX5MnNTNVmUNPLnkielra0=; b=N7nxCALdyfkB4kjyQpAPG8oGeGiM2N5usrExBdOLiek/UhUGZ31J4gEC VPqthDlBSqaSkqrCooUdR1mvD1mDd4MSxuyXJLeuPKAgAl4v2Mio8HTEQ gMpjfg6sacyM0rcD1iO951v+8UAjHwz79SELDQ/JMvd/rSl06U5wgp88h naGCHhXJmFB1TvRKw5xg6antWgNZZVJTmXgJ026VXgSJBiiDaw5rrDbMy ClrYRkTahv9KmlzDG1fLz1IYVPLK83bObIdKibys1iwAlYr6S5A651JVs fgnyGyE8eRzglyNyJCM/wI1tcXYIf5O6P+bSDA4Wp3/1iXEQP9m+sqlUy w==; X-IronPort-AV: E=McAfee;i="6500,9779,10503"; a="370042966" X-IronPort-AV: E=Sophos;i="5.95,192,1661842800"; d="scan'208";a="370042966" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Oct 2022 09:20:12 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10503"; a="606182872" X-IronPort-AV: E=Sophos;i="5.95,192,1661842800"; d="scan'208";a="606182872" Received: from dludovic-mobl1.ger.corp.intel.com (HELO box.shutemov.name) ([10.252.44.179]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Oct 2022 09:19:58 -0700 Received: by box.shutemov.name (Postfix, from userid 1000) id EC9CB1045CA; Mon, 17 Oct 2022 19:19:55 +0300 (+03) Date: Mon, 17 Oct 2022 19:19:55 +0300 From: "Kirill A . Shutemov" To: Vlastimil Babka Cc: Chao Peng , 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, Paolo Bonzini , Jonathan Corbet , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H . Peter Anvin" , Hugh Dickins , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vishal Annapurve , Yu Zhang , luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, david@redhat.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, Quentin Perret , Michael Roth , mhocko@suse.com, Muchun Song , wei.w.wang@intel.com Subject: Re: [PATCH v8 1/8] mm/memfd: Introduce userspace inaccessible memfd Message-ID: <20221017161955.t4gditaztbwijgcn@box.shutemov.name> References: <20220915142913.2213336-1-chao.p.peng@linux.intel.com> <20220915142913.2213336-2-chao.p.peng@linux.intel.com> 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-kernel@vger.kernel.org On Mon, Oct 17, 2022 at 03:00:21PM +0200, Vlastimil Babka wrote: > On 9/15/22 16:29, Chao Peng wrote: > > From: "Kirill A. Shutemov" > > > > KVM can use memfd-provided memory for guest memory. For normal userspace > > accessible memory, KVM userspace (e.g. QEMU) mmaps the memfd into its > > virtual address space and then tells KVM to use the virtual address to > > setup the mapping in the secondary page table (e.g. EPT). > > > > With confidential computing technologies like Intel TDX, the > > memfd-provided memory may be encrypted with special key for special > > software domain (e.g. KVM guest) and is not expected to be directly > > accessed by userspace. Precisely, userspace access to such encrypted > > memory may lead to host crash so it should be prevented. > > > > This patch introduces userspace inaccessible memfd (created with > > MFD_INACCESSIBLE). Its memory is inaccessible from userspace through > > ordinary MMU access (e.g. read/write/mmap) but can be accessed via > > in-kernel interface so KVM can directly interact with core-mm without > > the need to map the memory into KVM userspace. > > > > It provides semantics required for KVM guest private(encrypted) memory > > support that a file descriptor with this flag set is going to be used as > > the source of guest memory in confidential computing environments such > > as Intel TDX/AMD SEV. > > > > KVM userspace is still in charge of the lifecycle of the memfd. It > > should pass the opened fd to KVM. KVM uses the kernel APIs newly added > > in this patch to obtain the physical memory address and then populate > > the secondary page table entries. > > > > The userspace inaccessible memfd can be fallocate-ed and hole-punched > > from userspace. When hole-punching happens, KVM can get notified through > > inaccessible_notifier it then gets chance to remove any mapped entries > > of the range in the secondary page tables. > > > > The userspace inaccessible memfd itself is implemented as a shim layer > > on top of real memory file systems like tmpfs/hugetlbfs but this patch > > only implemented tmpfs. The allocated memory is currently marked as > > unmovable and unevictable, this is required for current confidential > > usage. But in future this might be changed. > > > > Signed-off-by: Kirill A. Shutemov > > Signed-off-by: Chao Peng > > --- > > ... > > > +static long inaccessible_fallocate(struct file *file, int mode, > > + loff_t offset, loff_t len) > > +{ > > + struct inaccessible_data *data = file->f_mapping->private_data; > > + struct file *memfd = data->memfd; > > + int ret; > > + > > + if (mode & FALLOC_FL_PUNCH_HOLE) { > > + if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len)) > > + return -EINVAL; > > + } > > + > > + ret = memfd->f_op->fallocate(memfd, mode, offset, len); > > + inaccessible_notifier_invalidate(data, offset, offset + len); > > Wonder if invalidate should precede the actual hole punch, otherwise we open > a window where the page tables point to memory no longer valid? Yes, you are right. Thanks for catching this. > > + return ret; > > +} > > + > > ... > > > + > > +static struct file_system_type inaccessible_fs = { > > + .owner = THIS_MODULE, > > + .name = "[inaccessible]", > > Dunno where exactly is this name visible, but shouldn't it better be > "[memfd:inaccessible]"? Maybe. And skip brackets. > > > + .init_fs_context = inaccessible_init_fs_context, > > + .kill_sb = kill_anon_super, > > +}; > > + > -- Kiryl Shutsemau / Kirill A. Shutemov