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 43523C46467 for ; Wed, 23 Nov 2022 18:19:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239553AbiKWSTI (ORCPT ); Wed, 23 Nov 2022 13:19:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239637AbiKWSSs (ORCPT ); Wed, 23 Nov 2022 13:18:48 -0500 Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1BF1711A0F; Wed, 23 Nov 2022 10:18:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1669227527; x=1700763527; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=E89CZqbaoYjUKLoTevrvJoCvfEz61O1bB0tNgiHnTvA=; b=ih6tOimMX0Pm8MMJOQndqTCFsJ96W3582sK4vUi3UCEWpOtxdgi775lD 7NFKcxByfHrOiwkngDSO6mTPdHUpJnB5JR+jleZDKzQJkUPLJDX/U0SCo epTX3uXQNVPHPvm45Ur3rSXH0ypR9SIGiKP5yvN9vkfFNZNXUZfsMt+X1 7mqJOv91VajbGTxg32SMNwJ1+SutDKBJAI+osyeJBmCBWrq4huOBChPaW rai9sfoaSuxMem2HqBbU8YTChqQDR9xImENGZEJaqLs7waopMvdvx4OF7 gbsm0hL48PGTJyqn3/bbqleWVg90ilbzqmGwhlJtaGQn2p697nv4sw49h A==; X-IronPort-AV: E=McAfee;i="6500,9779,10540"; a="294519300" X-IronPort-AV: E=Sophos;i="5.96,187,1665471600"; d="scan'208";a="294519300" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Nov 2022 10:18:46 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10540"; a="672965938" X-IronPort-AV: E=Sophos;i="5.96,187,1665471600"; d="scan'208";a="672965938" Received: from vcbudden-mobl3.amr.corp.intel.com (HELO [10.212.129.67]) ([10.212.129.67]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Nov 2022 10:18:45 -0800 Message-ID: <2d99f823-09bb-ff51-0e71-f254cc6ad28b@intel.com> Date: Wed, 23 Nov 2022 10:18:45 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [PATCH v7 06/20] x86/virt/tdx: Shut down TDX module in case of error Content-Language: en-US To: Sean Christopherson Cc: "Huang, Kai" , "peterz@infradead.org" , "kvm@vger.kernel.org" , "Luck, Tony" , "bagasdotme@gmail.com" , "ak@linux.intel.com" , "Wysocki, Rafael J" , "linux-kernel@vger.kernel.org" , "Chatre, Reinette" , "pbonzini@redhat.com" , "linux-mm@kvack.org" , "Yamahata, Isaku" , "kirill.shutemov@linux.intel.com" , "Shahar, Sagi" , "imammedo@redhat.com" , "Gao, Chao" , "Brown, Len" , "sathyanarayanan.kuppuswamy@linux.intel.com" , "Huang, Ying" , "Williams, Dan J" References: <48505089b645019a734d85c2c29f3c8ae2dbd6bd.1668988357.git.kai.huang@intel.com> <52b2be9b-defd-63ce-4cb2-96cd624a95a6@intel.com> <791bf9a2-a079-3cd6-90a3-42dbb332a38c@intel.com> <9f1ea2639839305dd8b82694b3d8c697803f43a1.camel@intel.com> <168ca2b3-ffac-31c4-0b83-2d0ee75f34a5@intel.com> From: Dave Hansen In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/23/22 09:37, Sean Christopherson wrote: > On Wed, Nov 23, 2022, Dave Hansen wrote: >> There's no way we can guarantee _that_. For one, the PAMT* allocations >> can always fail. I guess we could ask sysadmins to fire up a guest to >> "prime" things, but that seems a little silly. Maybe that would work as >> the initial implementation that we merge, but I suspect our users will >> demand more determinism, maybe a boot or module parameter. > Oh, you mean all of TDX initialization? I thought "initialization" here mean just > doing tdx_enable(). Yes, but the first call to tdx_enable() does TDH_SYS_INIT and all the subsequent work to get the module going. > Yeah, that's not going to be a viable option. Aside from lacking determinisim, > it would be all too easy to end up on a system with fragmented memory that can't > allocate the PAMTs post-boot. For now, the post-boot runtime PAMT allocations are the one any only way that TDX can be initialized. I pushed for it to be done this way. Here's why: Doing tdx_enable() is relatively slow and it eats up a non-zero amount of physically contiguous RAM for metadata (~1/256th or ~0.4% of RAM). Systems that support TDX but will never run TDX guests should not pay that cost. That means that we either make folks opt-in at boot-time or we try to make a best effort at runtime to do the metadata allocations. >From my perspective, the best-effort stuff is absolutely needed. Users are going to forget the command-line opt in and there's no harm in _trying_ the big allocations even if they fail. Second, in reality, the "real" systems that can run TDX guests are probably not going to sit around fragmenting memory for a month before they run their first guest. They're going to run one shortly after they boot when memory isn't fragmented and the best-effort allocation will work really well. Third, if anyone *REALLY* cared to make it reliable *and* wanted to sit around fragmenting memory for a month, they could just start a TDX guest and kill it to get TDX initialized. This isn't ideal. But, to me, it beats defining some new, separate ABI (or boot/module option) to do it. So, let's have those discussions. Long-term, what *is* the most reliable way to get the TDX module loaded with 100% determinism? What new ABI or interfaces are needed? Also, is that 100% determinism required the moment this series is merged? Or, can we work up to it? I think it can wait until this particular series is farther along.