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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 1D037C433B4 for ; Tue, 18 May 2021 22:32:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EDF1A611B0 for ; Tue, 18 May 2021 22:32:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352760AbhERWd2 (ORCPT ); Tue, 18 May 2021 18:33:28 -0400 Received: from mga18.intel.com ([134.134.136.126]:43856 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237154AbhERWd0 (ORCPT ); Tue, 18 May 2021 18:33:26 -0400 IronPort-SDR: 0AKGjXjITwaCIWogiSAgKBCqlPdsf7n2KeLuK2+ySjYSCc4K0Y4DaTQGA1tfCtLUkZ5D7t0oOx pY8HWrxfvdLw== X-IronPort-AV: E=McAfee;i="6200,9189,9988"; a="188247135" X-IronPort-AV: E=Sophos;i="5.82,310,1613462400"; d="scan'208";a="188247135" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2021 15:31:51 -0700 IronPort-SDR: 8U5S8hYSriIPi/gZaFWO+9xVutNW5JvYrpmgC3OQ7CxFP8z/ERZ2ZNm6N/lzXru+OHvvJj++CL whtXtmB8ShGA== X-IronPort-AV: E=Sophos;i="5.82,310,1613462400"; d="scan'208";a="542156624" Received: from craigsmi-mobl.amr.corp.intel.com (HELO [10.212.132.228]) ([10.212.132.228]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2021 15:31:50 -0700 Subject: Re: [RFC v2-fix 1/1] x86/tdx: Make DMA pages shared To: "Kuppuswamy, Sathyanarayanan" , Sean Christopherson Cc: Peter Zijlstra , Andy Lutomirski , Tony Luck , Andi Kleen , Kirill Shutemov , Kuppuswamy Sathyanarayanan , Dan Williams , Raj Ashok , linux-kernel@vger.kernel.org, Kai Huang , Sean Christopherson References: <1ccf5e60d2d79308d50f93c8c3b32b1394bc7baf.1619458733.git.sathyanarayanan.kuppuswamy@linux.intel.com> <20210518011912.259112-1-sathyanarayanan.kuppuswamy@linux.intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/18/21 3:12 PM, Kuppuswamy, Sathyanarayanan wrote: > "TDX is similar. In TDX architecture, the private guest memory is > encrypted, which prevents anything other than guest from > accessing/modifying it. So to communicate with I/O devices, we need > to create decrypted mapping and make the pages shared." That's actually even more wrong. :( Check out "Machine Check Architecture Background" in the TDX architecture spec. Modification is totally permitted in the architecture. A host can write all day long to guest memory. Depending on how you use the word, "access" can also include writes. TDX really just prevents guests from *consuming* the gunk that an attacker might write. Also, don't say "decrypted". The memory is probably still TME-enabled and probably encrypted on the DIMM. It's still encrypted even if shared, it's just using the TME key, not the TD key.