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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Fri, 8 Nov 2019 14:03:42 +0100
Message-ID: <CAKv+Gu-03HLED79e+V2D5BtSjRwHH7=rnUWyqZ7dBBD-s7RowQ@mail.gmail.com>
Subject: Re: [PATCH v4 1/1] arm64: Implement archrandom.h for ARMv8.5-RNG
To:     Richard Henderson <richard.henderson@linaro.org>,
        Marc Zyngier <maz@kernel.org>
Cc:     linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>, Mark Rutland <mark.rutland@arm.com>
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On Fri, 8 Nov 2019 at 12:10, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 11/6/19 10:30 PM, Ard Biesheuvel wrote:
> > On Wed, 6 Nov 2019 at 15:20, Richard Henderson
> > <richard.henderson@linaro.org> wrote:
> >> +static inline bool has_random(void)
> >> +{
> >> +       /*
> >> +        * We "have" RNG if either
> >> +        * (1) every cpu in the system has RNG, or
> >> +        * (2) in a non-preemptable context, current cpu has RNG.
> >> +        * Case 1 is the expected case when RNG is deployed, but
> >> +        * case 2 is present as a backup in case some big/little
> >> +        * system only has RNG on big cpus, we can still add entropy
> >> +        * from the interrupt handler of the big cpus.
> >
> > I don't understand the reference to the interrupt handler here.
>
> To add_interrupt_randomness(), invoked by handle_irq_event_percpu().
> Better if I reword the above to include the function name?
>

This is one of the several places where arch_random_get_seed_long() is
called, so if you are going to single it out like that, it does make
sense to clarify that.

> > It is
> > worth mentioning though that this arrangement permits
> > rand_initialize() to use the instructions regardless of whether they
> > are implemented only by the boot CPU or by all of them.
>
> Yes, I'll include that.
>
>
> r~