PentiumPro CR4 bugs and System Management Mode

Mikael Pettersson (mikpe@csd.uu.se)
Sat, 30 Oct 1999 20:47:10 +0200 (MET DST)

Is it possible for Linux to detect transitions to and from System
Management Mode (SMM) on Intel processors, and to execute Linux-
specific code before entering SMM and directly after exiting SMM?
Failing that, is it possible for Linux to detect if SMM is
implemented in the current system?

The reason I'm asking is that there are several errata [1] for the
Pentium Pro processor which affect control register CR4 and SMM.
In particular, errata 26 implies that CR4.PCE must not be set to
allow the RDPMC instruction in user-mode, and errata 56 implies
that all CR4 settings may be lost after transiting to and from SMM.

[1] Pentium Pro Processor Specification Update, January 1999.
Intel document number 242689-035.

/Mikael

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