From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.7 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 0B5AA7D912 for ; Tue, 27 Aug 2019 22:46:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726044AbfH0Wqc (ORCPT ); Tue, 27 Aug 2019 18:46:32 -0400 Received: from mga09.intel.com ([134.134.136.24]:33194 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725992AbfH0Wqc (ORCPT ); Tue, 27 Aug 2019 18:46:32 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 Aug 2019 15:46:31 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,439,1559545200"; d="scan'208";a="192396943" Received: from yyu32-desk1.sc.intel.com ([10.144.153.205]) by orsmga002.jf.intel.com with ESMTP; 27 Aug 2019 15:46:30 -0700 Message-ID: <6c3dc33e16c8bbb6d45c0a6ec7c684de197fa065.camel@intel.com> Subject: Re: [PATCH v8 11/27] x86/mm: Introduce _PAGE_DIRTY_SW From: Yu-cheng Yu To: Peter Zijlstra Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin Date: Tue, 27 Aug 2019 15:37:12 -0700 In-Reply-To: <20190823140233.GC2332@hirez.programming.kicks-ass.net> References: <20190813205225.12032-1-yu-cheng.yu@intel.com> <20190813205225.12032-12-yu-cheng.yu@intel.com> <20190823140233.GC2332@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.1-2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Fri, 2019-08-23 at 16:02 +0200, Peter Zijlstra wrote: > On Tue, Aug 13, 2019 at 01:52:09PM -0700, Yu-cheng Yu wrote: > > > +static inline pte_t pte_move_flags(pte_t pte, pteval_t from, pteval_t to) > > +{ > > + if (pte_flags(pte) & from) > > + pte = pte_set_flags(pte_clear_flags(pte, from), to); > > + return pte; > > +} > > Aside of the whole conditional thing (I agree it would be better to have > this unconditionally); the function doesn't really do as advertised. > > That is, if @from is clear, it doesn't endeavour to make sure @to is > also clear. > > Now it might be sufficient, but in that case it really needs a comment > and or different name. > > An implementation that actually moves the bit is something like: > > pteval_t a,b; > > a = native_pte_value(pte); > b = (a >> from_bit) & 1; > a &= ~((1ULL << from_bit) | (1ULL << to_bit)); > a |= b << to_bit; > return make_native_pte(a); There can be places calling pte_wrprotect() on a PTE that is already RO + DIRTY_SW. Then in pte_move_flags(pte, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW) we do not want to clear _PAGE_DIRTY_SW. But, I will look into this and make it more obvious. Thanks, Yu-cheng