Intel SL8K2 Specification Update - Page 56

Errata R R76. L-bit of the CS and LMA bit of the IA32_EFER Register May Have an Erroneous Value For One Instruction Following a Mode Transition in a Hyper-Threading Enabled Processor Supporting Intel® Extended Memory 64 Technology (Intel® EM64T) Problem: In an Intel® EM64T enabled Processor, the L-bit of the Code Segment (CS) descriptor may not update with the correct value in an HT environment. This may occur in a small window when one logical processor is making a transition from compatibility mode to 64-bit mode (or vice-versa) while the other logical processor is being stalled. A similar problem may occur for the observation of the EFER.LMA bit by the decode logic. Implication: The first instruction following a mode transition may be decoded as if it was still in the previous mode. For example, this may result in an incorrect stack size used for a stack operation, i.e. a write of only 4-bytes and an adjustment to ESP of only 4 in 64-bit mode. The problem can manifest itself, however, on any instruction which would behave differently in 64-bit mode than in compatibility mode. Workaround: It is possible for the BIOS to contain a workaround for this erratum. Status: For the steppings affected, see the Summary Tables of Changes. R77. Memory Ordering Failure May Occur with Snoop Filtering Third Party Agents after Issuing and Completing a BWIL (Bus Write Invalidate Line) or BLW (Bus Locked Write) Transaction Problem: Under limited circumstances, the processors may, after issuing and completing a BWIL or BLW transaction, retain data from the addressed cache line in shared state even though the specification requires complete invalidation. This data retention may also occur when a BWIL transaction's self-snooping yields HITM snoop results. Implication: A system may suffer memory ordering failures if its central agent incorporates coherence sequencing which depends on full self-invalidation of the cache line associated (1) with BWIL and BLW transactions, or (2) all HITM snoop results without regard to the transaction type and snoop results source. Workaround: 1. The central agent can issue a bus cycle that causes a cache line to be invalidated (Bus Read Invalidate Line (BRIL) or BWIL transaction) in response to a processor-generated BWIL (or BLW) transaction to insure complete invalidation of the associated cache line. If there are no intervening processor-originated transactions to that cache line, the central agent's invalidating snoop will get a clean snoop result. Or 2. Snoop filtering central agents can: a. Not use processor-originated BWIL or BLW transactions to update their snoop filter information, or b. Update the associated cache line state information to shared state on the originating bus (rather than invalid state) in reaction to a BWIL or BLW. Status: For the steppings affected, see the Summary Tables of Changes. 56 Intel® Pentium® 4 Processor on 90 nm Process Specification Update