Re: [PATCH] random: do not use jump labels before they are initialized

From: Ard Biesheuvel <ardb@kernel.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Stephen Boyd <swboyd@chromium.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Russell King <linux@armlinux.org.uk>,
	Arnd Bergmann <arnd@arndb.de>, Phil Elwell <phil@raspberrypi.com>
Subject: Re: [PATCH] random: do not use jump labels before they are initialized
Date: Tue, 7 Jun 2022 14:03:28 +0200	[thread overview]
Message-ID: <CAMj1kXF7NToZgAW66puCOwc1+d7ZTmVm_CbDYEeH+j0XJH1vug@mail.gmail.com> (raw)
In-Reply-To: <Yp839NjwW3scZEqi@zx2c4.com>

On Tue, 7 Jun 2022 at 13:35, Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> Hi Ard,
>
> On Tue, Jun 07, 2022 at 01:10:52PM +0200, Ard Biesheuvel wrote:
> > Fair enough. What I would like is to remove the need to play around
> > with the placement of jump_label_init() across architectures. Jump
> > labels are fundamentally a performance optimization, so unless you can
> > explain how setting it as early as possible makes a material
> > difference, performance or otherwise, I really think we should pursue
> > a solution that does the static key manipulation at some later time.
>
> Alright. It sounds like Catalin also prefers the same. This seems simple
> enough with minimal downsides: https://lore.kernel.org/lkml/20220607113238.769088-1-Jason@zx2c4.com/
>

That looks simple enough. Do we risk causing any boot stalls due to
the crediting being deferred? Or new warnings about randomness being
used before CRNG is ready?

> So maybe we should just go that route.
>

It is not my preferred approach, but I can live with it.