linux-kernel - Re: [PATCH v2 4/5] arm64: Add support for SMCCC TRNG entropy source

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Message-ID: <20201105134142.GA4856@sirena.org.uk>
Date:   Thu, 5 Nov 2020 13:41:42 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Andre Przywara <andre.przywara@....com>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v2 4/5] arm64: Add support for SMCCC TRNG entropy source

On Thu, Nov 05, 2020 at 12:56:55PM +0000, Andre Przywara wrote:

>  static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
>  {
> +	struct arm_smccc_res res;
>  	unsigned long val;
> -	bool ok = arch_get_random_seed_long(&val);
>  
> -	*v = val;
> -	return ok;
> +	if (cpus_have_const_cap(ARM64_HAS_RNG)) {
> +		if (arch_get_random_seed_long(&val)) {
> +			*v = val;
> +			return true;
> +		}
> +		return false;
> +	}

It isn't obvious to me why we don't fall through to trying the SMCCC
TRNG here if for some reason the v8.5-RNG didn't give us something.
Definitely an obscure possibility but still...

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