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

[Khalid Aziz]

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