[v6 11/15] arm64/kasan: explicitly zero kasan shadow memory

[Pasha Tatashin]

Hi Will,

 > Damn, I actually prefer the flag :)
 >
 > But actually, if you look at our implementation of vmemmap_populate, 
then we
 > have our own version of vmemmap_populate_basepages that terminates at the
 > pmd level anyway if ARM64_SWAPPER_USES_SECTION_MAPS. If there's 
resistance
 > to do this in the core code, then I'd be inclined to replace our
 > vmemmap_populate implementation in the arm64 code with a single 
version that
 > can terminate at either the PMD or the PTE level, and do zeroing if
 > required. We're already special-casing it, so we don't really lose 
anything
 > imo.

Another approach is to create a new mapping interface for kasan only. As 
what Ard Biesheuvel wrote:

 > KASAN uses vmemmap_populate as a convenience: kasan has nothing to do
 > with vmemmap, but the function already existed and happened to do what
 > KASAN requires.
 >
 > Given that that will no longer be the case, it would be far better to
 > stop using vmemmap_populate altogether, and clone it into a KASAN
 > specific version (with an appropriate name) with the zeroing folded
 > into it.

I agree with this statement, but I think it should not be part of this 
project.

Pasha