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 73458C433EF for ; Thu, 2 Jun 2022 10:11:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233434AbiFBKLQ (ORCPT ); Thu, 2 Jun 2022 06:11:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42440 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230406AbiFBKLN (ORCPT ); Thu, 2 Jun 2022 06:11:13 -0400 Received: from mga06.intel.com (mga06b.intel.com [134.134.136.31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CED7D2AD5C2; Thu, 2 Jun 2022 03:11:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1654164672; x=1685700672; h=date:from:to:cc:subject:message-id:reply-to:references: mime-version:in-reply-to; bh=da86tUUULUVat8HuHmdIwGDy5StYU/aEj+aL1ESVKiM=; b=fHDYKqgFDHVQviH6ChjxYfgt1oORIuPN7lRKfUdcYRYt40abOD/amhhf C5eF6K4qDsSlNQIHbJ87jbtAbaEDOf3T0ifprAkgruf8hhUI7tOT2H6Rt nwk9Pm6SEFSQnfsSEFX/2Q9i1O3ZtiB5TmYPM3fPmpCQdHP03GLUMYO+z SYdKNyzIVd22JepgAltlTJ8wS5cBW3NUVY5kBQoAEgpQfdqvEql9Rqau/ Yyn7PIgh9sOTldkumprPtotX0p6oeKVLQZiBQVDG/2qSdYYhBnp2zMRAC WGFg9t80LwiWeCvx91frsgzmYOHucZqd6ZeU2s+jrIhoAIYa0R+b0oaYm g==; X-IronPort-AV: E=McAfee;i="6400,9594,10365"; a="336560321" X-IronPort-AV: E=Sophos;i="5.91,270,1647327600"; d="scan'208";a="336560321" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Jun 2022 03:11:08 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.91,270,1647327600"; d="scan'208";a="721237238" Received: from chaop.bj.intel.com (HELO localhost) ([10.240.192.101]) by fmsmga001.fm.intel.com with ESMTP; 02 Jun 2022 03:10:58 -0700 Date: Thu, 2 Jun 2022 18:07:33 +0800 From: Chao Peng To: "Gupta, Pankaj" Cc: Vishal Annapurve , 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 , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Yu Zhang , "Kirill A . Shutemov" , Andy Lutomirski , Jun Nakajima , 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 Subject: Re: [PATCH v6 3/8] mm/memfd: Introduce MFD_INACCESSIBLE flag Message-ID: <20220602100733.GA1296997@chaop.bj.intel.com> Reply-To: Chao Peng References: <20220519153713.819591-1-chao.p.peng@linux.intel.com> <20220519153713.819591-4-chao.p.peng@linux.intel.com> <20220601101747.GA1255243@chaop.bj.intel.com> <1f1b17e8-a16d-c029-88e0-01f522cc077a@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1f1b17e8-a16d-c029-88e0-01f522cc077a@amd.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 01, 2022 at 02:11:42PM +0200, Gupta, Pankaj wrote: > > > > > Introduce a new memfd_create() flag indicating the content of the > > > > created memfd is inaccessible from userspace through ordinary MMU > > > > access (e.g., read/write/mmap). However, the file content can be > > > > accessed via a different mechanism (e.g. KVM MMU) indirectly. > > > > > > > > > > SEV, TDX, pkvm and software-only VMs seem to have usecases to set up > > > initial guest boot memory with the needed blobs. > > > TDX already supports a KVM IOCTL to transfer contents to private > > > memory using the TDX module but rest of the implementations will need > > > to invent > > > a way to do this. > > > > There are some discussions in https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.org%2Flkml%2F2022%2F5%2F9%2F1292&data=05%7C01%7Cpankaj.gupta%40amd.com%7Cb81ef334e2dd44c6143308da43b87d17%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637896756895977587%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=oQbM2Hj7GlhJTwnTM%2FPnwsfJlmTL7JR9ULBysAqm6V8%3D&reserved=0 > > already. I somehow agree with Sean. TDX is using an dedicated ioctl to > > copy guest boot memory to private fd so the rest can do that similarly. > > The concern is the performance (extra memcpy) but it's trivial since the > > initial guest payload is usually optimized in size. > > > > > > > > Is there a plan to support a common implementation for either allowing > > > initial write access from userspace to private fd or adding a KVM > > > IOCTL to transfer contents to such a file, > > > as part of this series through future revisions? > > > > Indeed, adding pre-boot private memory populating on current design > > isn't impossible, but there are still some opens, e.g. how to expose > > private fd to userspace for access, pKVM and CC usages may have > > different requirements. Before that's well-studied I would tend to not > > add that and instead use an ioctl to copy. Whether we need a generic > > ioctl or feature-specific ioctl, I don't have strong opinion here. > > Current TDX uses a feature-specific ioctl so it's not covered in this > > series. > > Common function or ioctl to populate preboot private memory actually makes > sense. > > Sorry, did not follow much of TDX code yet, Is it possible to filter out > the current TDX specific ioctl to common function so that it can be used by > other technologies? TDX code is here: https://patchwork.kernel.org/project/kvm/patch/70ed041fd47c1f7571aa259450b3f9244edda48d.1651774250.git.isaku.yamahata@intel.com/ AFAICS It might be possible to filter that out to a common function. But would like to hear from Paolo/Sean for their opinion. Chao > > Thanks, > Pankaj