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

[Rob Gardner]

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