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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 4A3B1C2BB1D for ; Mon, 16 Mar 2020 23:59:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1868B20663 for ; Mon, 16 Mar 2020 23:59:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733042AbgCPX7f (ORCPT ); Mon, 16 Mar 2020 19:59:35 -0400 Received: from mga06.intel.com ([134.134.136.31]:48081 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732932AbgCPX7f (ORCPT ); Mon, 16 Mar 2020 19:59:35 -0400 IronPort-SDR: rzKtaOE/4Ri3zXuy263VksSdMeBJ7wjvonGcL1F1CV5OHOJxe8PWrHXFrIK8CWZnTSkkO+L0HX nOI9CzZdDlLQ== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Mar 2020 16:59:34 -0700 IronPort-SDR: EXC5OOzw7kiXij0nmleAvE4HV7gl1QOatOdI+iOuUlgq374R5zeDr8XW1LmjOeNWMBJmjRY+II 7ydyTJgBvJ/w== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,562,1574150400"; d="scan'208";a="233334574" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga007.jf.intel.com with ESMTP; 16 Mar 2020 16:59:34 -0700 Date: Mon, 16 Mar 2020 16:59:34 -0700 From: Sean Christopherson To: "Xing, Cedric" Cc: Jarkko Sakkinen , 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 , Jethro Beekman , Connor Kuehl , Harald Hoyer , Lily Sturmann Subject: Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX enclave call Message-ID: <20200316235934.GM24267@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> <94ce05323c4de721c4a6347223885f2ad9f541af.camel@linux.intel.com> <5dc2ec4bc9433f9beae824759f411c32b45d4b74.camel@linux.intel.com> <20200316225322.GJ24267@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) 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 04:50:26PM -0700, Xing, Cedric wrote: > On 3/16/2020 3:53 PM, Sean Christopherson wrote: > >On Mon, Mar 16, 2020 at 11:38:24PM +0200, Jarkko Sakkinen wrote: > >>>My suggestions explicitly maintained robustness, and in fact increased > >>>it. If you think we've lost capability, please speak with specificity > >>>rather than in vague generalities. Under my suggestions we can: > >>>1. call the vDSO from C > >>>2. pass context to the handler > >>>3. have additional stack manipulation options in the handler > >>> > >>>The cost for this is a net 2 additional instructions. No existing > >>>capability is lost. > >> > >>My vague generality in this case is just that the whole design > >>approach so far has been to minimize the amount of wrapping to > >>EENTER. > > > >Yes and no. If we wanted to minimize the amount of wrapping around the > >vDSO's ENCLU then we wouldn't have the exit handler shenanigans in the > >first place. The whole process has been about balancing the wants of each > >use case against the overall quality of the API and code. > > > The design of this vDSO API was NOT to minimize wrapping, but to allow > maximal flexibility. More specifically, we strove not to restrict how info > was exchanged between the enclave and its host process. After all, calling > convention is compiler specific - i.e. the enclave could be built by a > different compiler (e.g. MSVC) that doesn't share the same list of CSRs as > the host process. Therefore, the API has been implemented to pass through > virtually all registers except those used by EENTER itself. Similarly, all > registers are passed back from enclave to the caller (or the exit handler) > except those used by EEXIT. %rbp is an exception because the vDSO API has to > anchor the stack, using either %rsp or %rbp. We picked %rbp to allow the > enclave to allocate space on the stack. And unless I'm missing something, using %rcx to pass @leaf would still satisfy the above, correct? Ditto for saving/restoring %rbx. I.e. a runtime that's designed to work with enclave's using a different calling convention wouldn't be able to take advantage of being able to call the vDSO from C, but neither would it take on any meaningful burden.