linux-kernel - Re: [PATCH v6 06/17] timekeeping: add raw clock fallback for random_get

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Date:   Mon, 25 Apr 2022 14:37:11 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        arnd@...db.de
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH v6 06/17] timekeeping: add raw clock fallback for
 random_get_entropy()

On Sat, Apr 23 2022 at 23:26, Jason A. Donenfeld wrote:
> The addition of random_get_entropy_fallback() provides access to
> whichever time source has the highest frequency, which is useful for
> gathering entropy on platforms without available cycle counters. It's
> not necessarily as good as being able to quickly access a cycle counter
> that the CPU has, but it's still something, even when it falls back to
> being jiffies-based.
>
> In the event that a given arch does not define get_cycles(), falling
> back to the get_cycles() default implementation that returns 0 is really
> not the best we can do. Instead, at least calling
> random_get_entropy_fallback() would be preferable, because that always
> needs to return _something_, even falling back to jiffies eventually.
> It's not as though random_get_entropy_fallback() is super high precision
> or guaranteed to be entropic, but basically anything that's not zero all
> the time is better than returning zero all the time.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Theodore Ts'o <tytso@....edu>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>

Not that I care much, but in general taking over authorship w/o
attribution via Suggested-by or such is frowned upon.

Thanks,

        tglx