Re: Can KEY_DH_OPERATIONS become tristate? (was: Re: Kernel 5.3.0 stuck during boot on Amiga)

[Geert Uytterhoeven]

Hi David,

On Wed, Sep 18, 2019 at 6:43 PM David Howells <dhowells@xxxxxxxxxx> wrote:
> Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> > > > TL;DR: CONFIG_CRYPTO_DH=y is reported to cause boot delays of several
> > > > minutes on old and slow machines.
> > >
> > > Why is it doing that?  It doesn't do anything unless it is called, so
> > > something must be calling it.
> >
> > I don't know.  Enabling initcall_debug shows that dh_init() takes a very long
> > time.
>
> Ah...  The bit that handles keyctl_dh_compute() doesn't do anything unless
> asked, but the bit in the crypto layer that does dh does (ie. dh_init()).  I
> guess it's doing some sort of self-test, but I can't see how it effects that.
> I think you need to consult the author/maintainer of crypto/dh.c.

Apparently the Debian kernel config had not enabled
CONFIG_CRYPTO_MANAGER_DISABLE_TESTS, so all crypto tests
were run at boot time :-(

> It might be possible to make CONFIG_KEY_DH_OPERATIONS not depend on
> CONFIG_CRYPTO_DH and have crypto_alloc_kpp() load the *crypto* part on
> demand.  Failing that, I can look into demand-loading keyctl operations.

Regardless, it may be a good idea to make KEY_DH_OPERATIONS tristate
one day, so enabling wireless as a module doesn't force CONFIG_CRYPTO_DH
builtin.

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds