Re: [PATCH] cpu/hw_random cleanups

[H. Peter Anvin]

Alan Cox wrote:
>>>For example, I wonder if storing Intel's cpuid(0x00000001) ecx
>>>register output is wise on older Intel cpus.  I worry about garbage
>>>appearing there.  Is that a false worry?
>>>
>>
>>Yes; it should be completely safe.
> 
> I have to admit I'd be more comfortable if we only set those bits IFF
> we know they are valid to check, not so much because we need to right now
> but out of a desire to make less mistakes possible
>

The problem is that you risk exactly the opposite mistake -- it's called
"anticompetitive feature lockout."  Intel would happily tell you to do
it; in fact, if you follow Intel guidelines or use their sample code it
will treat anything that isn't an Intel chip like a 486.

If any chip that claims to support CPUID level 00000001h reports
anything other than zero in this field, that chip is broken and we
should deal with it as a chip-specific bug.  At this point there are no
chips which are known to have this bug (and there are, after all, only a
finite number of chips out there.)

	-hpa