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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 25007C07E9B for ; Tue, 20 Jul 2021 21:24:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 017986023F for ; Tue, 20 Jul 2021 21:24:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231743AbhGTUnU (ORCPT ); Tue, 20 Jul 2021 16:43:20 -0400 Received: from mga18.intel.com ([134.134.136.126]:1142 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234287AbhGTUly (ORCPT ); Tue, 20 Jul 2021 16:41:54 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10051"; a="198601041" X-IronPort-AV: E=Sophos;i="5.84,256,1620716400"; d="scan'208";a="198601041" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Jul 2021 14:22:18 -0700 X-IronPort-AV: E=Sophos;i="5.84,256,1620716400"; d="scan'208";a="469903732" Received: from kvadariv-mobl1.amr.corp.intel.com (HELO [10.212.155.118]) ([10.212.155.118]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Jul 2021 14:22:17 -0700 Subject: Re: [PATCH v3 5/6] platform/x86: intel_tdx_attest: Add TDX Guest attestation interface driver To: Andi Kleen , "Kuppuswamy, Sathyanarayanan" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Peter Zijlstra , Andy Lutomirski , Hans de Goede , Mark Gross , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko Cc: Peter H Anvin , Tony Luck , Dan Williams , Kirill Shutemov , Sean Christopherson , Kuppuswamy Sathyanarayanan , x86@kernel.org, linux-kernel@vger.kernel.org, platform-driver-x86@vger.kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org References: <20210720045552.2124688-1-sathyanarayanan.kuppuswamy@linux.intel.com> <20210720045552.2124688-6-sathyanarayanan.kuppuswamy@linux.intel.com> <4c43dfe4-e44b-9d6d-b012-63790bb47b19@linux.intel.com> <52caa0e2-d3da-eef0-da5f-e83cc54c133c@intel.com> <4f8dc9dd-0dbc-bff9-570b-0d20f673d3f0@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: <4f8dc9dd-0dbc-bff9-570b-0d20f673d3f0@linux.intel.com> 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 7/20/21 2:16 PM, Andi Kleen wrote: > On 7/20/2021 10:59 AM, Dave Hansen wrote: >> On 7/20/21 10:52 AM, Kuppuswamy, Sathyanarayanan wrote: >>>> Why does this need to use the page allocator directly? >> ^^ You didn't address this question. > > The address needs to be naturally aligned, and I'm not sure all slab > allocators guarantee 64 byte alignment. So using the page allocator > seems to be safer. I guess a comment would be good. The documentation > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/core-api/memory-allocation.rst#n146 claims: > The address of a chunk allocated with `kmalloc` is aligned to at least > ARCH_KMALLOC_MINALIGN bytes. For sizes which are a power of two, the > alignment is also guaranteed to be at least the respective size. This is another case where care in coding these things up, writing good changelogs and expressing assumptions in comments can save back-and-forth from a reviewer. Imagine if this had been: /* * tdreport_data needs to be 64-byte aligned. * Full page alignment is more than enough. */ tdreport_data = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 0); if (!tdreport_data) { ret = -ENOMEM; goto failed; }