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 C613AC433B4 for ; Fri, 23 Apr 2021 01:21:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 87B8461445 for ; Fri, 23 Apr 2021 01:21:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236777AbhDWBVr (ORCPT ); Thu, 22 Apr 2021 21:21:47 -0400 Received: from mga18.intel.com ([134.134.136.126]:10186 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229888AbhDWBVq (ORCPT ); Thu, 22 Apr 2021 21:21:46 -0400 IronPort-SDR: /n/kcIECIxNBrVAWBu9/zdPHhKYRIGwDOYld+V2K/PsFda2zgTLk4mMpqdB9uM0ECxGp62JJ0x vbFeF/KATKKg== X-IronPort-AV: E=McAfee;i="6200,9189,9962"; a="183483037" X-IronPort-AV: E=Sophos;i="5.82,244,1613462400"; d="scan'208";a="183483037" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Apr 2021 18:21:11 -0700 IronPort-SDR: KFejdVgSI4A2TicxB4czpczmqaesg3Y/ADFCslHGeofbgkbaIwZ7nZhiEKiNsxeIGiFb3lgLHu oamHqkAA20ZQ== X-IronPort-AV: E=Sophos;i="5.82,244,1613462400"; d="scan'208";a="384951187" Received: from anashraf-mobl.amr.corp.intel.com (HELO [10.213.177.111]) ([10.213.177.111]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Apr 2021 18:21:09 -0700 Subject: Re: [PATCH v2 1/1] x86/tdx: Add __tdcall() and __tdvmcall() helper functions To: "Kuppuswamy, Sathyanarayanan" , Peter Zijlstra , Andy Lutomirski Cc: Andi Kleen , Kirill Shutemov , Kuppuswamy Sathyanarayanan , Dan Williams , Raj Ashok , Sean Christopherson , linux-kernel@vger.kernel.org References: <8723950c-e07c-9a03-503a-ab232701d1e9@linux.intel.com> <77a13ae9-0220-030e-7ae4-fd26edd7b110@intel.com> <2a3f6b3d-cd80-0734-ce83-c067666c8326@linux.intel.com> <14332abf-c78c-3bc2-9a7c-ceacfa7a0661@intel.com> <596175e3-9d1e-6c9c-fadb-ad02c396e3ad@linux.intel.com> <9161efc0-fd25-d239-32b7-5d2c726579b0@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: <9161efc0-fd25-d239-32b7-5d2c726579b0@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 4/22/21 6:09 PM, Kuppuswamy, Sathyanarayanan wrote: > But let me try to explain it here. What I meant by complication is, > for in/out instruction, we use alternative_io() to substitute in/out > instructions with tdg_in()/tdg_out() assembly calls. So we have to ensure > that we don't corrupt registers or stack from the substituted instructions > > If you check the implementation of tdg_in()/tdg_out(), you will notice > that we have added code to preserve the caller registers. So, if we use > C wrapper for this use case, there is a chance that it might mess > the caller registers or stack. > >     alternative_io("in" #bwl " %w2, %" #bw "0",            \ >             "call tdg_in" #bwl, X86_FEATURE_TDX_GUEST,    \ >             "=a"(value), "d"(port)) Are you saying that calling C functions from inline assembly might corrupt the stack or registers? Are you suggesting that you simply can't call C functions from inline assembly? Or, that you can't express the register clobbers of a function call in inline assembly? You might want to check around the kernel to see how other folks do it.