Intel X5472 Specification Update - Page 21

AX11. The Processor May Report a #TS Instead of a #GP Fault Problem: A jump to a busy TSS (Task-State Segment) may cause a #TS (invalid TSS exception) instead of a #GP fault (general protection exception). Implication: Operation systems that access a busy TSS may get invalid TSS fault instead of a #GP fault. Intel has not observed this erratum with any commercially available software. Workaround: None identified. Status: For the steppings affected, see the Summary Tables of Changes. AX12. Code Segment Limit Violation May Occur on 4 Gigabyte Limit Check Problem: Code Segment limit violation may occur on 4 Gigabyte limit check when the code stream wraps around in a way that one instruction ends at the last byte of the segment and the next instruction begins at 0x0. Implication: This is a rare condition that may result in a system hang. Intel has not observed this erratum with any commercially available software, or system. Workaround: Avoid code that wraps around segment limit. Status: For the steppings affected, see the Summary Tables of Changes. AX13. A Write to an APIC Register Sometimes May Appear to Have Not Occurred Problem: With respect to the retirement of instructions, stores to the uncacheable memorybased APIC register space are handled in a non-synchronized way. For example if an instruction that masks the interrupt flag, for example, CLI is executed soon after an uncacheable write to the Task Priority Register (TPR) that lowers the APIC priority, the interrupt masking operation may take effect before the actual priority has been lowered. This may cause interrupts whose priority is lower than the initial TPR, but higher than the final TPR, to not be serviced until the interrupt enabled flag is finally set, i.e. by STI instruction. Interrupts will remain pending and are not lost. Implication: In this example the processor may allow interrupts to be accepted but may delay their service. Workaround: This non-synchronization can be avoided by issuing an APIC register read after the APIC register write. This will force the store to the APIC register before any subsequent instructions are executed. No commercial operating system is known to be impacted by this erratum. Status: For the steppings affected, see the Summary Tables of Changes. AX14. Last Branch Records (LBR) Updates May be Incorrect after a Task Switch Problem: A Task-State Segment (TSS) task switch may incorrectly set the LBR_FROM value to the LBR_TO value. Implication: The LBR_FROM will have the incorrect address of the Branch Instruction. Workaround: None identified. Status: For the steppings affected, see the Summary Tables of Changes. AX15. Problem: REP MOVS/STOS Executing with Fast Strings Enabled and Crossing Page Boundaries with Inconsistent Memory Types may use an Incorrect Data Size or Lead to Memory-Ordering Violations. Under certain conditions as described in the Software Developers Manual section "Outof-Order Stores For String Operations in Pentium 4, Intel Xeon, and P6 Family 21 Intel® Xeon® Processor 5400 Series Specification Update