Intel X3330 Specification Update - Page 32

and spans multiple 16-byte boundaries, may cause a machine check exception or a system hang. Implication: Due to this erratum, a machine check exception or a system hang may occur. 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. AAA53. An Enabled Debug Breakpoint or Single Step Trap May Be Taken after MOV SS/POP SS Instruction if it is Followed by an Instruction That Signals a Floating Point Exception Problem: A MOV SS/POP SS instruction should inhibit all interrupts including debug breakpoints until after execution of the following instruction. This is intended to allow the sequential execution of MOV SS/POP SS and MOV [r/e]SP, [r/e]BP instructions without having an invalid stack during interrupt handling. However, an enabled debug breakpoint or single step trap may be taken after MOV SS/POP SS if this instruction is followed by an instruction that signals a floating point exception rather than a MOV [r/e]SP, [r/e]BP instruction. This results in a debug exception being signaled on an unexpected instruction boundary since the MOV SS/POP SS and the following instruction should be executed atomically. Implication: This can result in incorrect signaling of a debug exception and possibly a mismatched Stack Segment and Stack Pointer. If MOV SS/POP SS is not followed by a MOV [r/e]SP, [r/e]BP, there may be a mismatched Stack Segment and Stack Pointer on any exception. Intel has not observed this erratum with any commercially available software, or system. Workaround: As recommended in the IA32 Intel® Architecture Software Developer's Manual, the use of MOV SS/POP SS in conjunction with MOV [r/e]SP, [r/e]BP will avoid the failure since the MOV [r/e]SP, [r/e]BP will not generate a floating point exception. Developers of debug tools should be aware of the potential incorrect debug event signaling created by this erratum. Status: For the steppings affected, see the Summary Tables of Changes. AAA54. IA32_MC1_STATUS MSR Bit[60] Does Not Reflect Machine Check Error Reporting Enable Correctly Problem: IA32_MC1_STATUS MSR (405H) bit[60] (EN- Error Enabled) is supposed to indicate whether the enable bit in the IA32_MC1_CTL MSR (404H) was set at the time of the last update to the IA32_MC1_STATUS MSR. Due to this erratum, IA32_MC1_STATUS MSR bit[60] instead reports the current value of the IA32_MC1_CTL MSR enable bit. Implication: IA32_MC1_STATUS MSR bit [60] may not reflect the correct state of the enable bit in the IA32_MC1_CTL MSR at the time of the last update. Workaround: None identified. Status: For the steppings affected, see the Summary Tables of Changes. AAA55. Problem: A VM Exit Due to a Fault While Delivering a Software Interrupt May Save Incorrect Data into the VMCS If a fault occurs during delivery of a software interrupt (INTn) in virtual-8086 mode when virtual mode extensions are in effect and that fault causes a VM exit, incorrect data may be saved into the VMCS. Specifically, information about the software interrupt may not be reported in the IDT-vectoring information field. In addition, the interruptibility-state field may indicate blocking by STI or by MOV SS if such blocking were in effect before execution of the INTn instruction or before execution of the VMentry instruction that injected the software interrupt. 32 Intel® Xeon® Processor 3300 Series Specification Update January 2012