Re: Userspace notifications for observing userfaultfd faults

[Robert O'Callahan]

On Wed, May 12, 2021 at 6:12 AM Axel Rasmussen <axelrasmussen@xxxxxxxxxx> wrote:
> Is some combination of bpf and kprobes a possible solution? There are
> some seemingly relevant examples here:
> https://github.com/iovisor/bpftrace/blob/master/docs/tutorial_one_liners.md
>
> I haven't tried it, but it seems like attaching to handle_userfault()
> would give similar information to perf_count_sw_page_faults, but for
> userfaults.

That would probably work in some cases, but as Kyle said that requires
privileges and currently rr can run unprivileged (if you set
perf_event_paranoid to 1 or less) and usually does. Also, AFAIK,
kprobing handle_userfault would not be a stable ABI.

Rob