Re: [PATCH v12 0/4] x86: Capability bits fix and required bits sanity check

[Andi Kleen]

I'm not sure what the point of this check is. Obviously the kernel cannot
handle it, short of refusing to boot which would be far too drastic.

And if it's just for having something in the kernel log, who would look
for this? Any possible symptoms from a bogus cpuid will be far
disconnected from that particular log location.

Further, there's also no evidence that it is a real practical problem.
If anything it could likely only come from rogue VMMs, but these don't 
seem to be common. But VMMs normally don't really disable ISA, so even if the 
CPUID is inconsistent things will still likely work because the actual
instructions are fine.

Assuming it was a real problem, you could just do it in a user program, why
put it into the kernel and waste everyone's memory? (this cannot be
initcode due to hotplug)

Also it seems to violate Steinbach's system programing maxim
(never check for something you don't know how to handle)

-Andi