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

[Khalid Aziz]

On 03/07/2016 12:16 PM, David Miller wrote:
> From: Khalid Aziz <khalid.aziz@xxxxxxxxxx>
> Date: Mon, 7 Mar 2016 11:24:54 -0700
>
> > Tags can be cleared by user by setting tag to 0. Tags are
> > automatically cleared by the hardware when the mapping for a virtual
> > address is removed from TSB (which is why swappable pages are a
> > problem), so kernel does not have to do it as part of clean up.
>
> You might be able to crib some bits for the Tag in the swp_entry_t, it's
> 64-bit and you can therefore steal bits from the offset field.
>
> That way you'll have the ADI tag in the page tables, ready to re-install
> at swapin time.

That is a possibility but limited in scope. An address range covered by 
a single TTE can have large number of tags. Version tags are set on 
cacheline. In extreme case, one could set a tag for each set of 64-bytes 
in a page. Also tags are set completely in userspace and no transition 
occurs to kernel space, so kernel has no idea of what tags have been 
set. I have not found a way to query the MMU on tags.

I will think some more about it.

Thanks,
Khalid