From: Daniel Axtens
> Sent: 13 August 2020 12:37
>
> >> Seem like this could simply use a copy_to_user to further simplify
> >> things?
> >
> > I'll benchmark it and find out.
>
> I tried this:
>
> for (walk = head; walk; walk = walk->next) {
> - struct pollfd *fds = walk->entries;
> - int j;
> -
> - for (j = 0; j < walk->len; j++, ufds++)
> - if (__put_user(fds[j].revents, &ufds->revents))
> - goto out_fds;
> + if (copy_to_user(ufds, walk->entries,
> + sizeof(struct pollfd) * walk->len))
> + goto out_fds;
> + ufds += walk->len;
> }
>
> With that approach, the poll2 microbenchmark (which polls 128 fds) is
> about as fast as v1.
>
> However, the poll1 microbenchmark, which polls just 1 fd, regresses a
> touch (<1% - ~2%) compared to the current code, although it's largely
> within the noise. Thoughts?
Is that with or without 'user copy hardening'?
Or use __copy_to_user() to skip all that 'crap'.
David
-
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