Re: [RFC 00/20] TLB batching consolidation and enhancements

Peter Zijlstra
2021-02-01T12:46:06Z

On Sun, Jan 31, 2021 at 07:57:01AM +0000, Nadav Amit wrote:
> > On Jan 30, 2021, at 7:30 PM, Nicholas Piggin <npiggin@gmail.com> wrote:

> > I'll go through the patches a bit more closely when they all come
> > through. Sparc and powerpc of course need the arch lazy mode to get
> > per-page/pte information for operations that are not freeing pages,
> > which is what mmu gather is designed for.
>
> IIUC you mean any PTE change requires a TLB flush. Even setting up a new PTE
> where no previous PTE was set, right?

These are the HASH architectures. Their hardware doesn't walk the
page-tables, but it consults a hash-table to resolve page translations.

They _MUST_ flush the entries under the PTL to avoid ever seeing
conflicting information, which will make them really unhappy. They can
do this because they have TLBI broadcast.

There's a few more details I'm sure, but those seem to have slipped from
my mind.