Messages in this thread | | | Date | Sun, 6 Oct 2019 20:21:03 +0200 | From | Pavel Machek <> | Subject | Re: x86/random: Speculation to the rescue |
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On Sun 2019-10-06 11:06:38, Linus Torvalds wrote: > On Sun, Oct 6, 2019 at 10:35 AM Pavel Machek <pavel@ucw.cz> wrote: > > > > It will not: boot is now halted because systemd wants some > > entropy. Everything is idle and very little interrupts are > > happening. We have spinning rust, but it is idle, and thus not > > generating any interrupts. > > Yes, but we have that problem now solved. > > Except on embedded platforms that have garbage CPU's without even a > cycle counter. > > But those won't have spinning rust anyway. > > Yes, bad SSD's and MMC disks (that they do have) will generate timing > noise too, but in the absense of a cycle counter, that noise won't be > much use.
Even without cycle counter... if we _know_ we are trying to generate entropy and have MMC available, we don't care about power and performance.
So we can just...
issue read request on MMC while (!interrupt_done) i++ ...and then use i++ as poor man's version of cycle counter.
[We would not want to do that in normal operation, for obvious reasons, just when userland is blocked and waiting for entropy.]
Hmm?
Best regards, Pavel
-- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html [unhandled content-type:application/pgp-signature] | |