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=0.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,HK_RANDOM_FROM, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 8C3D8C10DCE for ; Sun, 15 Mar 2020 17:53:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5464B20637 for ; Sun, 15 Mar 2020 17:53:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gwLvACi/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729011AbgCORxs (ORCPT ); Sun, 15 Mar 2020 13:53:48 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:53268 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728985AbgCORxr (ORCPT ); Sun, 15 Mar 2020 13:53:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1584294826; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=4sCAV6YPEIN4XPv5c8gxRua4pipL3WppoMnmoXzPK/Y=; b=gwLvACi/FapZ6/fjGzEYJhYtbAOvrPoqlx/QgHrk9cGpHR6SUrgjpe8DAWgAVKj0zRNRcM f33m3+DIQocwGRoPbsLTJSkc1gCr0HH7mrglrvooWHnqi0obKWwiJu7NuaWfbS6KlfLFD2 aS7+xvWTv5goFLEicMZtdq3yLYh6ZjE= Received: from mail-io1-f71.google.com (mail-io1-f71.google.com [209.85.166.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-394-9PBbbQEiP66ti7Jz7OlvVw-1; Sun, 15 Mar 2020 13:53:44 -0400 X-MC-Unique: 9PBbbQEiP66ti7Jz7OlvVw-1 Received: by mail-io1-f71.google.com with SMTP id d16so10154775iop.17 for ; Sun, 15 Mar 2020 10:53:44 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=4sCAV6YPEIN4XPv5c8gxRua4pipL3WppoMnmoXzPK/Y=; b=opmVRA4susqzl5IA+npZAFPUQBsXbQnTRsAlDcpjT9lQeWV2/ONqif7TLOuU+XD6dx 3AUH9XWoV+VtCnyY3B0DfcCnh00lVZZHmERKod7fV3P4AY4flGLjhT7fODr9+LR9IGpD cQ9+I4iNb1VBgFkP6Bp5SXu0hYPTzgoNJbUwp+ypGkKzp2dYAX+IFTa38cb8gk/ifZ0c bWHinvA5wtIW1BUl52o8QaQHuz9PYzyyq5Bt6vDqOPt3N2k02IF4C0QkLt6NjWPyxCcD Uhoxpecgpw8pePRIFjOt+QBCJdJhTSbbh1ZGVfcZnB7Bf8Wljh78yLGGRdAkR1kGFger 4JYw== X-Gm-Message-State: ANhLgQ0jZ+qqLE5lDuajy2yBeZJdgftPYXhm88ffcXwTwzCRvURPphOy uR+NMYVmUQ14dGj1sGPEXRZGglF8O2EIsfxyLN2ByQpUAMbn+9HzdB2f+BbVvDIFVInVqHptacp foPF8jyfHf6/G5nr0y9nUk+RYeDG56Xs+H4qXo+Tp X-Received: by 2002:a05:6e02:685:: with SMTP id o5mr24142751ils.86.1584294824283; Sun, 15 Mar 2020 10:53:44 -0700 (PDT) X-Google-Smtp-Source: ADFU+vv5rfYob+x+SH8BDGDVnTOHAxWdTolLX/Uz7HHyi5g6stxSZI9yXG9waJeMX3XmVStg/i9g2MSrXdDSJkvVEns= X-Received: by 2002:a05:6e02:685:: with SMTP id o5mr24142734ils.86.1584294824017; Sun, 15 Mar 2020 10:53:44 -0700 (PDT) MIME-Version: 1.0 References: <20200303233609.713348-1-jarkko.sakkinen@linux.intel.com> <20200303233609.713348-22-jarkko.sakkinen@linux.intel.com> <20200315012523.GC208715@linux.intel.com> In-Reply-To: <20200315012523.GC208715@linux.intel.com> From: Nathaniel McCallum Date: Sun, 15 Mar 2020 13:53:33 -0400 Message-ID: Subject: Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX enclave call To: Jarkko Sakkinen Cc: linux-kernel@vger.kernel.org, x86@kernel.org, linux-sgx@vger.kernel.org, akpm@linux-foundation.org, dave.hansen@intel.com, "Christopherson, Sean J" , 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 , cedric.xing@intel.com, Patrick Uiterwijk , Andy Lutomirski , Jethro Beekman , Connor Kuehl , Harald Hoyer , Lily Sturmann Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 14, 2020 at 9:25 PM Jarkko Sakkinen wrote: > > On Wed, Mar 11, 2020 at 01:30:07PM -0400, Nathaniel McCallum wrote: > > Currently, the selftest has a wrapper around > > __vdso_sgx_enter_enclave() which preserves all x86-64 ABI callee-saved > > registers (CSRs), though it uses none of them. Then it calls this > > function which uses %rbx but preserves none of the CSRs. Then it jumps > > into an enclave which zeroes all these registers before returning. > > Thus: > > > > 1. wrapper saves all CSRs > > 2. wrapper repositions stack arguments > > 3. __vdso_sgx_enter_enclave() modifies, but does not save %rbx > > 4. selftest zeros all CSRs > > 5. wrapper loads all CSRs > > > > I'd like to propose instead that the enclave be responsible for saving > > and restoring CSRs. So instead of the above we have: > > 1. __vdso_sgx_enter_enclave() saves %rbx > > 2. enclave saves CSRs > > 3. enclave loads CSRs > > 4. __vdso_sgx_enter_enclave() loads %rbx > > > > I know that lots of other stuff happens during enclave transitions, > > but at the very least we could reduce the number of instructions > > through this critical path. > > What Jethro said and also that it is a good general principle to cut > down the semantics of any vdso as minimal as possible. > > I.e. even if saving RBX would make somehow sense it *can* be left > out without loss in terms of what can be done with the vDSO. Please read the rest of the thread. Sean and I have hammered out some sensible and effective changes.