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

- From: Khalid Aziz \<hidden\>
- Date: 2016-03-07 21:07:37 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2016/03/4703288
- Thread: https://ratatoskr.run/sparclinux/2016/03/4699675/t.md

```text
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

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