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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 F2C2BC04AB4 for ; Fri, 17 May 2019 09:06:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CB30720868 for ; Fri, 17 May 2019 09:06:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728398AbfEQJGb convert rfc822-to-8bit (ORCPT ); Fri, 17 May 2019 05:06:31 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:58038 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728245AbfEQJGa (ORCPT ); Fri, 17 May 2019 05:06:30 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-51-y_73BxfGMMizl2DShogLcw-1; Fri, 17 May 2019 10:06:27 +0100 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 17 May 2019 10:06:26 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 17 May 2019 10:06:26 +0100 From: David Laight To: 'Jan Kara' , Dan Williams CC: "linux-nvdimm@lists.01.org" , "stable@vger.kernel.org" , Jeff Moyer , Ingo Molnar , Christoph Hellwig , Al Viro , Thomas Gleixner , Matthew Wilcox , Jeff Smits , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Kees Cook Subject: RE: [PATCH] libnvdimm/pmem: Bypass CONFIG_HARDENED_USERCOPY overhead Thread-Topic: [PATCH] libnvdimm/pmem: Bypass CONFIG_HARDENED_USERCOPY overhead Thread-Index: AQHVDI00Hs6UetBw5UmdJ+47dYtmSqZvBeSA Date: Fri, 17 May 2019 09:06:26 +0000 Message-ID: <2d8b1ba7890940bf8a512d4eef0d99b3@AcuMS.aculab.com> References: <155805321833.867447.3864104616303535270.stgit@dwillia2-desk3.amr.corp.intel.com> <20190517084739.GB20550@quack2.suse.cz> In-Reply-To: <20190517084739.GB20550@quack2.suse.cz> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-MC-Unique: y_73BxfGMMizl2DShogLcw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Jan Kara > Sent: 17 May 2019 09:48 ... > So this last paragraph is not obvious to me as check_copy_size() does a lot > of various checks in CONFIG_HARDENED_USERCOPY case. I agree that some of > those checks don't make sense for PMEM pages but I'd rather handle that by > refining check_copy_size() and check_object_size() functions to detect and > appropriately handle pmem pages rather that generally skip all the checks > in pmem_copy_from/to_iter(). And yes, every check in such hot path is going > to cost performance but that's what user asked for with > CONFIG_HARDENED_USERCOPY... Kees? Except that all the distros enable it by default. So you get the performance cost whether you (as a user) want it or not. I've changed some of our code to use __get_user() to avoid these stupid overheads. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)