Messages in this thread | | | Date | Thu, 13 Mar 2003 14:52:32 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] cpu/hw_random cleanups |
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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
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