[RFC PATCH 3/3] powerpc/64s/radix: optimise TLB flush with precise TLB ranges in mmu_gather

[Linus Torvalds]

On Tue, Jun 12, 2018 at 4:09 PM Nicholas Piggin <npiggin at gmail.com> wrote:
>
> Sorry I mean Intel needs the existing behaviour of range flush expanded
> to cover page table pages.... right?

Right.  Intel depends on the current thing, ie if a page table
*itself* is freed, we will will need to do a flush, but it's the exact
same flush as if there had been a regular page there.

That's already handled by (for example) pud_free_tlb() doing the
__tlb_adjust_range().

Again, I may be missing entirely what you're talking about, because it
feels like we're talking across each other.

My argument is that your new patches in (2-3 in the series - patch #1
looks ok) seem to be fundamentally specific to things that have a
*different* tlb invalidation for the directory entries than for the
leaf entries.

But that's not what at least x86 has, and not what the generic code has done.

I think it might be fine to introduce a few new helpers that end up
being no-ops for the traditional cases.

I just don't think it makes sense to maintain a set of range values
that then aren't actually used in the general case.

              Linus