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=-5.5 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 1B4DFC4338F for ; Wed, 28 Jul 2021 23:12:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E177960F9B for ; Wed, 28 Jul 2021 23:12:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232596AbhG1XMq (ORCPT ); Wed, 28 Jul 2021 19:12:46 -0400 Received: from mga07.intel.com ([134.134.136.100]:55857 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232392AbhG1XMp (ORCPT ); Wed, 28 Jul 2021 19:12:45 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10059"; a="276549632" X-IronPort-AV: E=Sophos;i="5.84,276,1620716400"; d="scan'208";a="276549632" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Jul 2021 16:12:42 -0700 X-IronPort-AV: E=Sophos;i="5.84,276,1620716400"; d="scan'208";a="581030981" Received: from shuangho-mobl1.amr.corp.intel.com (HELO [10.212.219.154]) ([10.212.219.154]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Jul 2021 16:12:41 -0700 Subject: Re: [PATCH v3 1/7] x86/sgx: Provide indication of life-cycle of EPC pages To: "Luck, Tony" , Sean Christopherson , Jarkko Sakkinen Cc: "x86@kernel.org" , "linux-kernel@vger.kernel.org" References: <20210719182009.1409895-1-tony.luck@intel.com> <20210728204653.1509010-1-tony.luck@intel.com> <20210728204653.1509010-2-tony.luck@intel.com> <17054ca5-0ef7-4b28-ab26-b1b96aa7403f@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: 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 7/28/21 3:57 PM, Luck, Tony wrote: >> Wouldn't it be safer to do something like: >> >> page->owner = owner ? owner : (void *)-1; >> >> -1 is non-NULL, but also invalid, which makes it harder for us to poke >> ourselves in the eye. > Does Linux have some #define INVALID_POINTER thing that > provides a guaranteed bad (e.g. non-canonical) value? > > (void *)-1 seems hacky. ERR_PTR(-SOMETHING) wouldn't be too bad. I guess it could even be: page->owner = ERR_PTR(SGX_EPC_PAGE_VA); and then: #define SGX_EPC_PAGE_VA 0xffff...something...greppable I *thought* we had a file full of these magic values, but maybe I'm misremembering the uapi magic header.