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

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Date:   Tue, 21 Jun 2022 19:22:56 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
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



Le 21/06/2022 à 20:47, Jason A. Donenfeld a écrit :
> 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).
> 

The fact that they are long lived make them a good candidate for 
memblock_alloc().

But fair enough, if they are not required that early then just do it later.

Christophe