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

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Message-ID: <13304.1568825025@warthog.procyon.org.uk>
Date:   Wed, 18 Sep 2019 17:43:45 +0100
From:   David Howells <dhowells@...hat.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     dhowells@...hat.com,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Michael Schmitz <schmitzmic@...il.com>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Can KEY_DH_OPERATIONS become tristate? (was: Re: Kernel 5.3.0 stuck during boot on Amiga)

Geert Uytterhoeven <geert@...ux-m68k.org> 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.

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.

David