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 A7556C433EF for ; Tue, 10 May 2022 10:42:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239975AbiEJKqQ (ORCPT ); Tue, 10 May 2022 06:46:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39850 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239882AbiEJKqO (ORCPT ); Tue, 10 May 2022 06:46:14 -0400 Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5C3AB28F1DB for ; Tue, 10 May 2022 03:42:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1652179337; x=1683715337; h=message-id:subject:from:to:cc:date:in-reply-to: references:mime-version:content-transfer-encoding; bh=A7b0wbGT99QIOnh89hBhN4ylBd9A+Bcmq8VgGdQf7N4=; b=Js/seXqFE4n+lOacFmBNMn5inpXFwgTtQehyBoWQKJW6Yp+jkznCVK2q mv0yuJ+Ee1E3AH6o7uKvcPvlxyRtZIsd7XQ6MVzNE4mxQyYHcLIvcQDlk HbdSGuC9VsdnmHbbGi+smSaFVKm5RqrO1MPtF/ABF+K+MUItBn6dSlRHH osqkqFo0bMHTmw/tf+DZ++ooPC23MORgsdO0lUI338msoaGjdtHUnMcwa fLP95ZQjquo+8pAhlKIi4g4uUPNPKK/lWatelY45HNA4cxXneUf2161g+ mNHhlR0qV7T9woh40burb/ZQ8dfH2TQIlcux5I3tn44sxgzb6CS/8s28u w==; X-IronPort-AV: E=McAfee;i="6400,9594,10342"; a="249864654" X-IronPort-AV: E=Sophos;i="5.91,214,1647327600"; d="scan'208";a="249864654" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 May 2022 03:42:17 -0700 X-IronPort-AV: E=Sophos;i="5.91,214,1647327600"; d="scan'208";a="602404116" Received: from aadavis-mobl1.amr.corp.intel.com (HELO khuang2-desk.gar.corp.intel.com) ([10.254.0.231]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 May 2022 03:42:12 -0700 Message-ID: <690ae2cb2099ac3e13c3da530a1b4a4eb5bafc5a.camel@intel.com> Subject: Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support From: Kai Huang To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Dave Hansen , Sathyanarayanan Kuppuswamy , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , Tony Luck , Andi Kleen , Wander Lairson Costa , Isaku Yamahata , marcelo.cerri@canonical.com, tim.gardner@canonical.com, khalid.elmously@canonical.com, philip.cox@canonical.com, linux-kernel@vger.kernel.org Date: Tue, 10 May 2022 22:42:10 +1200 In-Reply-To: <75d4755c9a376df2e98a267e10e60da3bd178b17.camel@intel.com> References: <20220503012721.ok7fbvxmnvsr6qny@box.shutemov.name> <58d07b2d-cef5-17ed-9c57-e12fe5665e04@intel.com> <40ccd0f0-35a1-5aa7-9e51-25ab196d79e5@linux.intel.com> <2ed5c9cc316950a5a47ee714715b7980f358a140.camel@intel.com> <20220507004236.5p5dyksftge7wwr3@black.fi.intel.com> <45d184273f1950320843f6696eb3071f7d354fd3.camel@intel.com> <20220509120927.7rg6v5pyc3f4pxsh@box.shutemov.name> <75d4755c9a376df2e98a267e10e60da3bd178b17.camel@intel.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 (3.42.4-1.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2022-05-10 at 11:54 +1200, Kai Huang wrote: > On Mon, 2022-05-09 at 15:09 +0300, Kirill A. Shutemov wrote: > > On Mon, May 09, 2022 at 03:37:22PM +1200, Kai Huang wrote: > > > On Sat, 2022-05-07 at 03:42 +0300, Kirill A. Shutemov wrote: > > > > On Fri, May 06, 2022 at 12:11:03PM +1200, Kai Huang wrote: > > > > > Kirill, what's your opinion? > > > > > > > > I said before that I think DMA API is the right tool here. > > > > > > > > Speculation about future of DMA in TDX is irrelevant here. If semantics > > > > change we will need to re-evaluate all users. VirtIO uses DMA API and it > > > > is conceptually the same use-case: communicate with the host. > > > > > > Virtio is designed for device driver to use, so it's fine to use DMA API. And > > > real DMA can happen to the virtio DMA buffers. Attestation doesn't have such > > > assumption. > > > > Whether attestation driver uses struct device is implementation detail. > > I don't see what is you point. > > No real DMA is involved in attestation. > > > > > > So I don't see why TD guest kernel cannot have a simple protocol to vmap() a > > > page (or couple of pages) as shared on-demand, like below: > > > > > > page = alloc_page(); > > > > > > addr = vmap(page, pgprot_decrypted(PAGE_KERNEL)); > > > > > > clflush_cache_range(page_address(page), PAGE_SIZE); > > > > > > MapGPA(page_to_phys(page) | cc_mkdec(0), PAGE_SIZE); > > > > > > And we can even avoid above clflush_cache_range() if I understand correctly. > > > > > > Or I missed something? > > > > For completeness, cover free path too. Are you going to opencode page > > accept too? > > Call __tdx_module_call(TDX_ACCEPT_PAGE, ...) right after MapGPA() to convert > back to private. I don't think there is any problem? > > > > > Private->Shared conversion is destructive. You have to split SEPT, flush > > TLB. Backward conversion even more costly. > > I think I won't call it destructive. > > And I suggested before, we can allocate a default size buffer (i.e. 4 pages), > which is large enough to cover all requests for now, during driver > initialization. This avoids IOCTL time conversion. We should still have code > in the IOCTL to check the request buffer size and when it is larger than the > default, the old should be freed a larger one should be allocated. But for now > this code path will never happen. > > Btw above is based on assumption that we don't support concurrent IOCTLs. This > version Sathya somehow changed to support concurrent IOCTLs but this was a > surprise as I thought we somehow agreed we don't need to support this. Hi Dave, Sorry I forgot to mention that GHCI 1.5 defines a generic TDVMCALL for a TD to communicate with VMM or another TD or some service in the host. This TDVMCALL can support many sub-commands. For now only sub-commands for TD migration is defined, but we can have more. For this, we cannot assume the size of the command buffer, and I don't see why we don't want to support concurrent TDVMCALLs. So looks from long term, we will very likely need IOCTL time buffer private-shared conversion. -- Thanks, -Kai