From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751385AbdHaAJa (ORCPT ); Wed, 30 Aug 2017 20:09:30 -0400 Received: from shards.monkeyblade.net ([184.105.139.130]:37426 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750761AbdHaAJ2 (ORCPT ); Wed, 30 Aug 2017 20:09:28 -0400 Date: Wed, 30 Aug 2017 17:09:25 -0700 (PDT) Message-Id: <20170830.170925.386619891775278628.davem@davemloft.net> To: khalid.aziz@oracle.com Cc: anthony.yznaga@oracle.com, dave.hansen@linux.intel.com, corbet@lwn.net, bob.picco@oracle.com, steven.sistare@oracle.com, pasha.tatashin@oracle.com, mike.kravetz@oracle.com, mingo@kernel.org, nitin.m.gupta@oracle.com, kirill.shutemov@linux.intel.com, tom.hromatka@oracle.com, eric.saint.etienne@oracle.com, allen.pais@oracle.com, cmetcalf@mellanox.com, akpm@linux-foundation.org, geert@linux-m68k.org, tklauser@distanz.ch, atish.patra@oracle.com, vijay.ac.kumar@oracle.com, peterz@infradead.org, mhocko@suse.com, jack@suse.cz, lstoakes@gmail.com, hughd@google.com, thomas.tai@oracle.com, paul.gortmaker@windriver.com, ross.zwisler@linux.intel.com, dave.jiang@intel.com, willy@infradead.org, ying.huang@intel.com, zhongjiang@huawei.com, minchan@kernel.org, vegard.nossum@oracle.com, imbrenda@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, aarcange@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, khalid@gonehiking.org Subject: Re: [PATCH v7 9/9] sparc64: Add support for ADI (Application Data Integrity) From: David Miller In-Reply-To: References: <7b8216b8-e732-0b31-a374-1a817d4fbc80@oracle.com> <20170830.153830.2267882580011615008.davem@davemloft.net> X-Mailer: Mew version 6.7 on Emacs 25.2 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Wed, 30 Aug 2017 17:09:27 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Khalid Aziz Date: Wed, 30 Aug 2017 17:23:37 -0600 > That is an interesting idea. This would enable TSTATE_MCDE on all > threads of a process as soon as one thread enables it. If we consider > the case where the parent creates a shared memory area and spawns a > bunch of threads. These threads access the shared memory without ADI > enabled. Now one of the threads decides to enable ADI on the shared > memory. As soon as it does that, we enable TSTATE_MCDE across all > threads and since threads are all using the same TTE for the shared > memory, every thread becomes subject to ADI verification. If one of > the other threads was in the middle of accessing the shared memory, it > will get a sigsegv. If we did not enable TSTATE_MCDE across all > threads, it could have continued execution without fault. In other > words, updating TSTATE_MCDE across all threads will eliminate the > option of running some threads with ADI enabled and some not while > accessing the same shared memory. This could be necessary at least for > short periods of time before threads can communicate with each other > and all switch to accessing shared memory with ADI enabled using same > tag. Does that sound like a valid use case or am I off in the weeds > here? A threaded application needs to synchronize and properly orchestrate access to shared memory. When a change is made to a mappping, in this case setting ADI attributes, it's being done for the address space not the thread. And the address space is shared amongst threads. Therefore ADI is not really a per-thread property but rather a per-address-space property.