Re: [PATCH 1/1] x86: replace RDRAND forced-reseed with simple sanity check

[Len Brown]

> If we trust built-in-self-test...
> why do we need to do this at all? We
> should check the return value at every call, anyway...

Yes, we do trust built-in-self-test.
Yes, we do check for errors on on every call, not just here in boot.

The sanity check at boot from the kernel allows Linux to disable
the feature, preventing user-space from thrashing trying to use it.

There is also a line of reasoning that if the circuit is going to fail,
chances are that it will fail immediately.
I have no reason to believe that the circuit will fail in the field
either at run-time or at boot-time.  But that line of reasoning
suggests that O(1 usec) to check at boot is a prudent investment --
it is certainly a better investment per time than may of the other
things Linux does.

thanks,
Len Brown, Intel Open Source Technology Center
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