linux-kernel - Re: [PATCH v5] powerpc/powernv: wire up rng during setup

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Date:   Tue, 21 Jun 2022 20:47:52 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH v5] powerpc/powernv: wire up rng during setup_arch

Hi Christophe,

On Tue, Jun 21, 2022 at 06:33:11PM +0000, Christophe Leroy wrote:
> Le 21/06/2022 à 16:08, Jason A. Donenfeld a écrit :
> > The platform's RNG must be available before random_init() in order to be
> > useful for initial seeding, which in turn means that it needs to be
> > called from setup_arch(), rather than from an init call. Fortunately,
> > each platform already has a setup_arch function pointer, which means we
> > can wire it up that way. Complicating things, however, is that POWER8
> > systems need some per-cpu state and kmalloc, which isn't available at
> > this stage. So we split things up into an early phase and a later
> > opportunistic phase. This commit also removes some noisy log messages
> > that don't add much.
> 
> Regarding the kmalloc(), I have not looked at it in details, but usually 
> you can use memblock_alloc() when kmalloc is not available yet.

That seems a bit excessive, especially as those allocations are long
lived. And we don't even *need* it that early, but just before
random_init(). Michael is running this v5 on the test rig overnight, so
we'll learn in the Australian morning whether this finally did the trick
(I hope).

Jason