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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E95A8C43332 for ; Wed, 18 Mar 2020 22:01:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B3F9420772 for ; Wed, 18 Mar 2020 22:01:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727224AbgCRWB0 (ORCPT ); Wed, 18 Mar 2020 18:01:26 -0400 Received: from mga07.intel.com ([134.134.136.100]:19359 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726619AbgCRWB0 (ORCPT ); Wed, 18 Mar 2020 18:01:26 -0400 IronPort-SDR: /qFH/8WYaDf8WdFopJwqO8iPeoOiObVOVwkjAM+xRk0JcETESwlaBLfx3GgU+pAA+4Hd7xNL9S zVSRtKUChNaw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2020 15:01:25 -0700 IronPort-SDR: Klu9TMou3EoHttQci5ZkRO0GJktwXeHEn6BrhsoQgdQ1qZn/HGT5fyX1pRRbe5f+p84CBjTjn1 GoGgtXe6EjpQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,569,1574150400"; d="scan'208";a="244961234" Received: from mbeldzik-mobl.ger.corp.intel.com (HELO localhost) ([10.252.55.127]) by orsmga003.jf.intel.com with ESMTP; 18 Mar 2020 15:01:15 -0700 Date: Thu, 19 Mar 2020 00:01:14 +0200 From: Jarkko Sakkinen To: "Xing, Cedric" Cc: Sean Christopherson , Jethro Beekman , Nathaniel McCallum , linux-kernel@vger.kernel.org, x86@kernel.org, linux-sgx@vger.kernel.org, akpm@linux-foundation.org, dave.hansen@intel.com, Neil Horman , "Huang, Haitao" , andriy.shevchenko@linux.intel.com, tglx@linutronix.de, "Svahn, Kai" , bp@alien8.de, Josh Triplett , luto@kernel.org, kai.huang@intel.com, David Rientjes , Patrick Uiterwijk , Andy Lutomirski , Connor Kuehl , Harald Hoyer , Lily Sturmann Subject: Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX enclave call Message-ID: <20200318220114.GB52244@linux.intel.com> References: <20200303233609.713348-1-jarkko.sakkinen@linux.intel.com> <20200303233609.713348-22-jarkko.sakkinen@linux.intel.com> <20200315012523.GC208715@linux.intel.com> <7f9f2efe-e9af-44da-6719-040600f5b351@fortanix.com> <20200316225534.GK24267@linux.intel.com> <7634c48d-a8e2-7366-6f04-06a27f8e5eaf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7634c48d-a8e2-7366-6f04-06a27f8e5eaf@intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 16, 2020 at 04:56:42PM -0700, Xing, Cedric wrote: > On 3/16/2020 3:55 PM, Sean Christopherson wrote: > > On Mon, Mar 16, 2020 at 02:31:36PM +0100, Jethro Beekman wrote: > > > Can someone remind me why we're not passing TCS in RBX but on the stack? > > > > I finally remembered why. It's pulled off the stack and passed into the > > exit handler. I'm pretty sure the vDSO could take it in %rbx and manually > > save it on the stack, but I'd rather keep the current behavior so that the > > vDSO is callable from C (assuming @leaf is changed to be passed via %rcx). > > > The idea is that the caller of this vDSO API is C callable, hence it cannot > receive TCS in %rbx anyway. Then it has to either MOV to %rbx or PUSH to > stack. Either way the complexity is the same. The vDSO API however has to > always save it on stack for exit handler. So receiving it via stack ends up > in simplest code. It is never C callable anyway given that not following the ABI so who cares about being C callable anyway? /Jarkko