Re: [PATCH] Re: UP APIC reenabling vs. cpu type detection ordering

From: H. Peter Anvin (
Date: Thu Feb 08 2001 - 00:06:47 EST

Mikael Pettersson wrote:
> H. Peter Anvin wrote:
> >"Maciej W. Rozycki" wrote:
> >...
> >> It might be viable just to delete the test altogether, though and just
> >> trap #GP(0) on the MSR access. For the sake of simplicity. If a problem
> >> with a system ever arizes, we may handle it then.
> >>
> >> Note that we still have to choose appropriate vendor-specific PeMo
> >> handling and an event for the NMI watchdog anyway.
> >
> >Right... if that is the case then it seems reasonable.
> No, poking into MSRs not explicitly defined on the current CPU is
> inherently unsafe. I have several x86 CPU data sheets here in front
> of me which say the same thing: "Don't write to undocumented MSRs."
> You cannot assume that every single x86 out there stays clear of
> all Intel-defined MSRs. Intel has also expanded this set over time:
> older designs may not even have known about the APIC_BASE MSR.

You misread me. "In that case it seems reasonable to do vendor-specific


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