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

[Rob Gardner <rob.gardner@oracle.com>]

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



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