Re: [PATCH v3 6/7] KVM: arm64: Participate in bitmap-based PTE aging

Oliver Upton
2024-04-02T07:00:34Z

On Tue, Apr 02, 2024 at 12:06:56AM -0400, Yu Zhao wrote:
> On Mon, Apr 1, 2024 at 7:30 PM James Houghton <jthoughton@google.com> wrote:
> > Suggested-by: Yu Zhao <yuzhao@google.com>
>
> Thanks but I did not suggest this.

Entirely up to you, but I would still want to credit everyone who
contributed to a feature even if the underlying implementation has
changed since the original attempt.

> What I have in v2 is RCU based. I hope Oliver or someone else can help
> make that work.

Why? If there's data to show that RCU has a material benefit over taking
the MMU lock for read then I'm all for it. Otherwise, the work required
to support page-table walkers entirely outside of the MMU lock isn't
justified.

In addition to ensuring that page table teardown is always RCU-safe,
we'd need to make sure all of the walkers that take the write lock are
prepared to handle races.

> Otherwise we can just drop this for now and revisit
> later.

I really wouldn't get hung up on the locking as the make-or-break for
whether arm64 supports this MMU notifier.

--
Thanks,
Oliver