From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751910AbdHaQk4 (ORCPT ); Thu, 31 Aug 2017 12:40:56 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:26371 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751717AbdHaQkx (ORCPT ); Thu, 31 Aug 2017 12:40:53 -0400 Subject: Re: [PATCH v7 9/9] sparc64: Add support for ADI (Application Data Integrity) To: David Miller 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 References: <7b8216b8-e732-0b31-a374-1a817d4fbc80@oracle.com> <20170830.153830.2267882580011615008.davem@davemloft.net> <20170830.170925.386619891775278628.davem@davemloft.net> From: Khalid Aziz Organization: Oracle Corp Message-ID: <3ff76988-43f2-85e4-eaf4-cc0d10b420a3@oracle.com> Date: Thu, 31 Aug 2017 10:38:30 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170830.170925.386619891775278628.davem@davemloft.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/30/2017 06:09 PM, David Miller wrote: > 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. > That does make sense. Thanks, Khalid