Subject: Re: [PATCH v2] sparc64: Add support for Application Data Integrity
 (ADI)
To: Dave Hansen <dave.hansen@linux.intel.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>
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 <CALCETrXey2_xEXhzjgHtZmf-dLp-9pec===d-8chLxrp8wgRXg@mail.gmail.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>,
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        Vineet.Gupta1@synopsys.com, Andrew Lutomirski <luto@kernel.org>,
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        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>,
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        linux-arch <linux-arch@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>
From: Khalid Aziz <khalid.aziz@oracle.com>
Organization: Oracle Corp
Message-ID: <56DDED63.8010302@oracle.com>
Date: Mon, 7 Mar 2016 14:06:43 -0700
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On 03/07/2016 10:46 AM, Dave Hansen wrote:
> 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?
>

Good questions. Isn't set of valid VAs already constrained by VA_BITS 
(set to 44 in arch/sparc/include/asm/processor_64.h)? As I see it we are 
already not using the top 4 bits. Please correct me if I am wrong.

Thanks,
Khalid