Intel architecture ia-32 User Manual

Vol. 3A 9-57

The BIOS is responsible for selecting an appropriate update block in the non-volatile storage for
storing the new update. This BIOS is also responsible for ensuring the integrity of the informa-
tion provided by the caller, including authenticating the proposed update before incorporating it
into storage.

Before writing the update block into NVRAM, the BIOS should ensure that the update structure
meets the following criteria in the following order:

1.

The update header version should be equal to an update header version recognized by the 
BIOS.

2.

The update loader version in the update header should be equal to the update loader 
version contained within the BIOS image.

3.

The update block must checksum. This checksum is computed as a 32-bit summation of all 
double words in the structure, including the header, data, and processor signature table.

The BIOS selects update block(s) in non-volatile storage for storing the candidate update. The
BIOS can select any available update block as long as it guarantees that only a single update
exists for any given processor stepping in non-volatile storage. If the update block selected
already contains an update, the following additional criteria apply to overwrite it:

•

The processor signature in the proposed update must be equal to the processor signature in
the header of the current update in NVRAM (Processor Signature + platform ID bits).

•

The update revision in the proposed update should be greater than the update revision in
the header of the current update in NVRAM.

STORAGE_FULL

The BIOS non-volatile storage area is unable to accommodate 
the update because all available update blocks are filled with 
updates that are needed for processors in the system.

CPU_NOT_PRESENT

The processor stepping does not currently exist in the system.

INVALID_HEADER

The update header contains a header or loader version that is 
not recognized by the BIOS.

INVALID_HEADER_CS

The update does not checksum correctly.

SECURITY_FAILURE

The processor rejected the update.

INVALID_REVISION

The same or more recent revision of the update exists in the 
storage device.