linux-kernel - Re: [PATCH] random: fix rdrand mix-in

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Message-ID: <CA+55aFwzbWgxrwRcErmFfu+9gRcFvujNJM8e5KyDjbEBmYkiBg@mail.gmail.com>
Date:   Tue, 17 Jul 2018 17:01:06 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Theodore Ts'o" <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jann Horn <jannh@...gle.com>, tcharding <me@...in.cc>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Eric Biggers <ebiggers@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] random: fix rdrand mix-in

On Tue, Jul 17, 2018 at 2:12 PM Theodore Y. Ts'o <tytso@....edu> wrote:
>
> I wasn't sure how quickly the HW entropy would replenish itself; I
> know that on first RDRAND platforms it would effectively never fail
> (as in if six of the eight cores were calling RDRAND in a tight loop
> _maybe_ you could exhaust the HW entropy).

I suspect you can't hit it in practice on Intel systems, but maybe you
can on others. And maybe future other architectures might be different
yet.

But rdrand has the potential of being pretty slow, and it's almost
certainly not worth continuing if it stopped giving us data.

                  Linus