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_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 67F28C10F0E for ; Thu, 18 Apr 2019 13:13:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 44174217FA for ; Thu, 18 Apr 2019 13:13:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389036AbfDRNNq convert rfc822-to-8bit (ORCPT ); Thu, 18 Apr 2019 09:13:46 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:38352 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388299AbfDRNNp (ORCPT ); Thu, 18 Apr 2019 09:13:45 -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-98-nwPXMM-9NGqHeOMqUFPXMA-1; Thu, 18 Apr 2019 14:13:42 +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; Thu, 18 Apr 2019 14:14:52 +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; Thu, 18 Apr 2019 14:14:52 +0100 From: David Laight To: 'Thomas Gleixner' CC: 'Fenghua Yu' , 'Ingo Molnar' , 'Borislav Petkov' , 'H Peter Anvin' , "'Paolo Bonzini'" , 'Dave Hansen' , 'Ashok Raj' , 'Peter Zijlstra' , 'Ravi V Shankar' , 'Xiaoyao Li ' , 'Christopherson Sean J' , 'Kalle Valo' , 'Michael Chan' , 'linux-kernel' , 'x86' , "'kvm@vger.kernel.org'" , "'netdev@vger.kernel.org'" , "'linux-wireless@vger.kernel.org'" Subject: RE: [PATCH v7 04/21] x86/split_lock: Align x86_capability to unsigned long to avoid split locked access Thread-Topic: [PATCH v7 04/21] x86/split_lock: Align x86_capability to unsigned long to avoid split locked access Thread-Index: AQHU9Wc8cfw3/6sx9k22vKHnyDMwNqZBowBwgAAfOzD///urAIAAIrYg Date: Thu, 18 Apr 2019 13:14:52 +0000 Message-ID: References: <1555536851-17462-1-git-send-email-fenghua.yu@intel.com> <1555536851-17462-5-git-send-email-fenghua.yu@intel.com> <698b9419c81b443fb9c180d2b27fd34a@AcuMS.aculab.com> In-Reply-To: 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: nwPXMM-9NGqHeOMqUFPXMA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Thomas Gleixner > Sent: 18 April 2019 12:49 > On Thu, 18 Apr 2019, David Laight wrote: > > From: David Laight > > > Sent: 18 April 2019 10:21 > > > From: Fenghua Yu > > > > Sent: 17 April 2019 22:34 > > > > > > > > set_cpu_cap() calls locked BTS and clear_cpu_cap() calls locked BTR to > > > > operate on bitmap defined in x86_capability. > > > > > > > > Locked BTS/BTR accesses a single unsigned long location. In 64-bit mode, > > > > the location is at: > > > > base address of x86_capability + (bit offset in x86_capability / 64) * 8 > > > > > > > > Since base address of x86_capability may not be aligned to unsigned long, > > > > the single unsigned long location may cross two cache lines and > > > > accessing the location by locked BTS/BTR introductions will cause > > > > split lock. > > > > > > Isn't the problem that the type (and definition) of x86_capability[] are wrong. > > > If the 'bitmap' functions are used for it, it should be defined as a bitmap. > > > This would make it 'unsigned long' not __u32. > > > > > > This type munging of bitmaps only works on LE systems. > > > > > > OTOH the locked BTS/BTR instructions could be changed to use 32 bit accesses. > > > ISTR some of the associated functions use byte accesses. > > > > > > Perhaps there ought to be asm wrappers for BTS/BTR that do 8bit and > > > 32bit accesses. > > > > A quick look shows that this isn't the only __32[] that is being > > cast to (unsigned long) and then to set/test/clear_bit() in those > > files. > > > > I wonder how much other code is applying such casts? > > The reason for the cpuid stuff using u32 is that this is actually the width > of the information retrieved from CPUID. Right, but you shouldn't (as has been found out) cast pointers to integer types. Running grep -r --include '*.[ch]' '_bit([^(]*, *([^)]* ' . over the entire kernel source tree shows quite a few 'dubious' casts. They'll be doubly dubious on BE systems. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)