Subject: Re: [PATCH v2] sparc64: Add support for Application Data Integrity
 (ADI)
To: Khalid Aziz <khalid.aziz@oracle.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Rob Gardner <rob.gardner@oracle.com>
References: <1456951177-23579-1-git-send-email-khalid.aziz@oracle.com>
 <20160305.230702.1325379875282120281.davem@davemloft.net>
 <56DD9949.1000106@oracle.com> <56DD9E94.70201@oracle.com>
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Cc: David Miller <davem@davemloft.net>, Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>, dingel@linux.vnet.ibm.com,
        zhenzhang.zhang@huawei.com, bob.picco@oracle.com,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        sparclinux@vger.kernel.org, Michal Hocko <mhocko@suse.cz>,
        chris.hyser@oracle.com, Richard Weinberger <richard@nod.at>,
        Vlastimil Babka <vbabka@suse.cz>,
        Konstantin Khlebnikov <koct9i@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Greg Thelen <gthelen@google.com>,
        Jan Kara <jack@suse.cz>, xiexiuqi@huawei.com,
        Vineet.Gupta1@synopsys.com, Andrew Lutomirski <luto@kernel.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>, bsegall@google.com,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>
From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <56DDBE68.6080709@linux.intel.com>
Date: Mon, 7 Mar 2016 09:46:16 -0800
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On 03/07/2016 08:06 AM, Khalid Aziz wrote:
> Top 4-bits of sparc64 virtual address are used for version tag only when
> a process has its PSTATE.mcde bit set and it is accessing a memory
> region that has ADI enabled on it (TTE.mcd set) and a version tag was
> set on the virtual address being accessed. These 4-bits retain their
> original semantics in all other cases.

OK, so this effectively reduces the address space of a process using the
feature.  Do we need to do anything explicit to keep an app from using
that address space?  Do we make sure the kernel doesn't place VMAs
there?  Do we respect mmap() hints that try to place memory there?