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From:   Tony Luck <tony.luck@gmail.com>
Date:   Thu, 20 Feb 2020 14:29:32 -0800
Message-ID: <CA+8MBbKyRhipHsxb0nvV11Bvv8ypQ_gq5JR8ihfuG6JfBTnxZw@mail.gmail.com>
Subject: Re: [PATCH] random: always use batched entropy for get_random_u{32,64}
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>, "Ted Ts'o" <tytso@mit.edu>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Also ... what's the deal with a spin_lock on a per-cpu structure?

        batch = raw_cpu_ptr(&batched_entropy_u64);
        spin_lock_irqsave(&batch->batch_lock, flags);
        if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
                extract_crng((u8 *)batch->entropy_u64);
                batch->position = 0;
        }
        ret = batch->entropy_u64[batch->position++];
        spin_unlock_irqrestore(&batch->batch_lock, flags);

Could we just disable interrupts and pre-emption around the entropy extraction?

-Tony