Re: [RFC PATCH v3] sparc64: Add support for Application Data Integrity (ADI)

[Khalid Aziz]

On 01/04/2017 04:49 PM, Dave Hansen wrote:
> On 01/04/2017 03:44 PM, Rob Gardner wrote:
> > On 01/04/2017 03:40 PM, Dave Hansen wrote:
> > > On 01/04/2017 03:35 PM, Rob Gardner wrote:
> > > > Tags are not cleared at all when memory is freed, but rather, lazily
> > > > (and automatically) cleared when memory is allocated.
> > > What does "allocated" mean in this context?  Physical or virtual? What
> > > does this do, for instance?
> >
> > The first time a virtual page is touched by a process after the malloc,
> > the kernel does clear_user_page() or something similar, which zeroes the
> > memory. At the same time, the memory tags are cleared.
>
> OK, so the tags can't survive a MADV_FREE.  That's definitely something
> for apps to understand that use MADV_FREE as a substitute for memset().
> It also means that tags can't be set for physically unallocated memory.
>
> Neither of those are deal killers, but it would be nice to document it.

This can go into the adi.txt doc file.

> How does this all work with large pages?

It works with large pages the same way as normal sized pages. The TTE 
for a large page also will have the mcd bit set in it and tags are set 
and referenced the same way.

--
Khalid