linux-kernel - Re: [PATCH v25 01/12] Linux Random Number Generator

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Message-ID: <alpine.DEB.2.21.1911161216540.14348@nanos.tec.linutronix.de>
Date:   Sat, 16 Nov 2019 12:25:21 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Stephan Müller <smueller@...onox.de>
cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Nicolai Stange <nstange@...e.de>,
        "Peter, Matthias" <matthias.peter@....bund.de>,
        Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        Roman Drahtmueller <draht@...altsekun.de>,
        Neil Horman <nhorman@...hat.com>
Subject: Re: [PATCH v25 01/12] Linux Random Number Generator

On Sat, 16 Nov 2019, Stephan Müller wrote:
> +/**
> + * Hot code path - Callback for interrupt handler
> + */
> +void add_interrupt_randomness(int irq, int irq_flags)
> +{
> +	lrng_time_process();
> +
> +	if (!lrng_pool_highres_timer()) {
> +		struct pt_regs *regs = get_irq_regs();
> +		static atomic_t reg_idx = ATOMIC_INIT(0);
> +		u64 ip;
> +
> +		lrng_pool_lfsr_u32(jiffies);
> +		lrng_pool_lfsr_u32(irq);
> +		lrng_pool_lfsr_u32(irq_flags);
> +
> +		if (regs) {
> +			u32 *ptr = (u32 *)regs;
> +			int reg_ptr = atomic_add_return_relaxed(1, &reg_idx);
> +			size_t n = (sizeof(struct pt_regs) / sizeof(u32));
> +
> +			ip = instruction_pointer(regs);
> +			lrng_pool_lfsr_u32(*(ptr + (reg_ptr % n)));
> +		} else
> +			ip = _RET_IP_;
> +
> +		lrng_pool_lfsr_u32(ip >> 32);
> +		lrng_pool_lfsr_u32(ip);
> +	}

Is there a way to avoid all that processing right in the interrupt hot
path and just store the raw data for later processing?

Thanks,

	tglx