Intel 64 and IA-32 Architectures Software Developers Manual Volume 3A, System Programming Guide, Part 1

Vol. 3A 9-47
PROCESSOR MANAGEMENT AND INITIALIZATION
all processors in the system. If a system design permits multiple steppings of
Pentium 4, Intel Xeon, and P6 family processors to exist concurrently; then the BIOS
must verify individual processors against the update header information to ensure
appropriate loading. Given these considerations, it is most practical to load the
update during MP initialization.
9.11.6.3 Update in a System Supporting Intel Hyper-Threading Technology
Intel Hyper-Threading Technology has implications on the loading of the microcode
update. The update must be loaded for each core in a physical processor. Thus, for a
processor supporting Hyper-Threading Technology, only one logical processor per
core is required to load the microcode update. Each individual logical processor can
independently load the update. However, MP initialization must provide some mech-
anism (e.g. a software semaphore) to force serialization of microcode update loads
and to prevent simultaneous load attempts to the same core.
9.11.6.4 Update in a System Supporting Dual-Core Technology
Dual-core technology has implications on the loading of the microcode update. The
microcode update facility is not shared between processor cores in the same physical
package. The update must be loaded for each core in a physical processor.
If processor core supports Hyper-Threading Technology, the guideline described in
Section 9.11.6.3 also applies.
9.11.6.5 Update Loader Enhancements
The update loader presented in Section 9.11.6, “Microcode Update Loader,” is a
minimal implementation that can be enhanced to provide additional functionality.
Potential enhancements are described below:
• BIOS can incorporate multiple updates to support multiple steppings of the
Pentium 4, Intel Xeon, and P6 family processors. This feature provides for
operating in a mixed stepping environment on an MP system and enables a user
to upgrade to a later version of the processor. In this case, modify the loader to
check the CPUID and platform ID bits of the processor that it is running on
against the available headers before loading a particular update. The number of
updates is only limited by available BIOS space.
• A loader can load the update and test the processor to determine if the update
was loaded correctly. See Section 9.11.7, “Update Signature and Verification.”
• A loader can verify the integrity of the update data by performing a checksum on
the double words of the update summing to zero. See Section 9.11.5, “Microcode
Update Checksum.”
• A loader can provide power-on messages indicating successful loading of an
update.