linux-kernel - Re: [PATCH v2] sparc64: Add support for Application Data Integrity (ADI)

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Date:	Mon, 7 Mar 2016 17:31:23 -0800
From:	Rob Gardner <rob.gardner@...cle.com>
To:	Khalid Aziz <khalid.aziz@...cle.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...capital.net>
Cc:	David Miller <davem@...emloft.net>,
	Jonathan Corbet <corbet@....net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	dingel@...ux.vnet.ibm.com, bob.picco@...cle.com,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Arnd Bergmann <arnd@...db.de>, sparclinux@...r.kernel.org,
	Michal Hocko <mhocko@...e.cz>, chris.hyser@...cle.com,
	Richard Weinberger <richard@....at>,
	Vlastimil Babka <vbabka@...e.cz>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Greg Thelen <gthelen@...gle.com>, Jan Kara <jack@...e.cz>,
	xiexiuqi@...wei.com, Vineet.Gupta1@...opsys.com,
	Andrew Lutomirski <luto@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, bsegall@...gle.com,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2] sparc64: Add support for Application Data Integrity
 (ADI)

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