From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030342AbdADXqD (ORCPT ); Wed, 4 Jan 2017 18:46:03 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:44650 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750774AbdADXp4 (ORCPT ); Wed, 4 Jan 2017 18:45:56 -0500 Subject: Re: [RFC PATCH v3] sparc64: Add support for Application Data Integrity (ADI) To: Dave Hansen , davem@davemloft.net, corbet@lwn.net, arnd@arndb.de, akpm@linux-foundation.org References: <1483569999-13543-1-git-send-email-khalid.aziz@oracle.com> <6fcaab9f-40fb-fdfb-2c7e-bf21a862ab7c@linux.intel.com> Cc: hpa@zytor.com, viro@zeniv.linux.org.uk, nitin.m.gupta@oracle.com, chris.hyser@oracle.com, tushar.n.dave@oracle.com, sowmini.varadhan@oracle.com, mike.kravetz@oracle.com, adam.buchbinder@gmail.com, minchan@kernel.org, hughd@google.com, kirill.shutemov@linux.intel.com, keescook@chromium.org, allen.pais@oracle.com, aryabinin@virtuozzo.com, atish.patra@oracle.com, joe@perches.com, pmladek@suse.com, jslaby@suse.cz, cmetcalf@mellanox.com, paul.gortmaker@windriver.com, mhocko@suse.com, jmarchan@redhat.com, lstoakes@gmail.com, 0x7f454c46@gmail.com, vbabka@suse.cz, tglx@linutronix.de, mingo@redhat.com, dan.j.williams@intel.com, iamjoonsoo.kim@lge.com, mgorman@techsingularity.net, vdavydov.dev@gmail.com, hannes@cmpxchg.org, namit@vmware.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, Khalid Aziz From: Khalid Aziz Organization: Oracle Corp Message-ID: Date: Wed, 4 Jan 2017 16:43:36 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <6fcaab9f-40fb-fdfb-2c7e-bf21a862ab7c@linux.intel.com> Content-Type: text/plain; charset=windows-1252; format=flowed 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 01/04/2017 04:27 PM, Dave Hansen wrote: > On 01/04/2017 02:46 PM, Khalid Aziz wrote: >> This patch extends mprotect to enable ADI (TSTATE.mcde), enable/disable >> MCD (Memory Corruption Detection) on selected memory ranges, enable >> TTE.mcd in PTEs, return ADI parameters to userspace and save/restore ADI >> version tags on page swap out/in. > > I'm a bit confused why we need all the mechanics with set_swp_pte_at(). > For pkeys, for instance, all of the PTEs under a given VMA share a pkey. > When swapping something in, we just get the pkey out of the VMA and > populate the PTE. > > ADI doesn't seem to have a similar restriction. The feature is turned > on or off at a VMA granularity, but we do not (or can enforce that all > pages under a given VMA must share a tag. > > But this leads to an interesting question: is the tag associated with > the (populated?) pte, or the virtual address? Can you have tags > associated with non-present addresses? What's the mechanism that clears > the tags at munmap() or MADV_FREE time? Hi Dave, Tag is associated with virtual address and all pages in a singular VMA do not share the same tag. When a page is swapped out, we need to save the tag that was set on it so we can restore it when we bring the page back in. When MMU translates a vitrtual address into physical address, it expects to see the same tag set on the physical page as is set in the VA before it will allow access. Tags are cleared on a page by NG4clear_page() and NG4clear_user_page() when a page is allocated to a task. > > Is the tag storage a precious resource? Can it be exhausted? There is a metadata area in RAM that stores the tags and it has enough space to cover all the tags for the RAM size. -- Khalid