Subject: Re: [PATCH v2] sparc64: Add support for Application Data Integrity
 (ADI)
To: Khalid Aziz <khalid.aziz@oracle.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@amacapital.net>
References: <1456951177-23579-1-git-send-email-khalid.aziz@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,
        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: Rob Gardner <rob.gardner@oracle.com>
Message-ID: <56DE2B6B.3050503@oracle.com>
Date: Mon, 7 Mar 2016 17:31:23 -0800
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On 03/07/2016 10:39 AM, Khalid Aziz wrote:
> On 03/07/2016 11:12 AM, Dave Hansen wrote:
>> On 03/07/2016 09:53 AM, Andy Lutomirski wrote:
>>> Also, what am I missing?  Tying these tags to the physical page seems
>>> like a poor design to me.  This seems really awkward to use.
>>
>> Yeah, can you describe the structures that store these things? Surely
>> the hardware has some kind of lookup tables for them and stores them in
>> memory _somewhere_.
>>
>
> Version tags are tied to virtual addresses, not physical pages.
>
> Where exactly are the tags stored is part of processor architecture 
> and I am not privy to that. MMU stores these lookup tables somewhere 
> and uses it to authenticate access to virtual addresses. It really is 
> irrelevant to kernel how MMU implements access controls as long as we 
> have access to the knowledge of how to use it.

The tags are stored in physical memory, and you can write a tag directly 
to that memory via stxa with ASI_MCD_REAL and completely bypass the MMU. 
When you do that, the tag will still be seen by any virtual address that 
maps to that physical address.

Rob