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From:   Thomas Gleixner <tglx@linutronix.de>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
        arnd@arndb.de
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH v6 06/17] timekeeping: add raw clock fallback for
 random_get_entropy()
In-Reply-To: <20220423212623.1957011-7-Jason@zx2c4.com>
References: <20220423212623.1957011-1-Jason@zx2c4.com>
 <20220423212623.1957011-7-Jason@zx2c4.com>
Date:   Mon, 25 Apr 2022 14:37:11 +0200
Message-ID: <87y1zt1gqw.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

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@linutronix.de>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.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