Specification Update 29
Errata
BG32. FREEZE_WHILE_SMM Does Not Prevent Event from Pending PEBS during SMM
Problem: In general, a PEBS record should be generated on the first count of the event after the
counter has overflowed. However, IA32_DEBUGCTL_MSR.FREEZE_WHILE_SMM (MSR
1D9H, bit [14]) prevents performance counters from counting during SMM (System
Management Mode). Due to this erratum, if
1. a performance counter overflowed before an SMI
2. a PEBS record has not yet been generated because another count of the event has
not occurred
3. the monitored event occurs during SMM
then a PEBS record will be saved after the next RSM instruction.
When FREEZE_WHILE_SMM is set, a PEBS should not be generated until the event
occurs outside of SMM.
Implication: A PEBS record may be saved after an RSM instruction due to the associated
performance counter detecting the monitored event during SMM; even when
FREEZE_WHILE_SMM is set.
Workaround:None identified.
Status: For the steppings affected, see the Summary Tables of Changes.
BG33. APIC Error “Received Illegal Vector” May Be Lost
Problem: APIC (Advanced Programmable Interrupt Controller) may not update the ESR (Error
Status Register) flag Received Illegal Vector bit [6] properly when an illegal vector error
is received on the same internal clock that the ESR is being written (as part of the
write-read ESR access flow). The corresponding error interrupt will also not be
generated for this case.
Implication: Due to this erratum, an incoming illegal vector error may not be logged into ESR
properly and may not generate an error interrupt.
Workaround:None identified.
Status: For the steppings affected, see the Summary Tables of Changes.
BG34. DR6 May Contain Incorrect Information When the First Instruction after a
MOV SS,r/m or POP SS Is a Store
Problem: Normally, each instruction clears the changes in DR6 (Debug Status Register) caused
by the previous instruction. However, the instruction following a MOV SS,r/m (MOV to
the stack segment selector) or POP SS (POP stack segment selector) instruction will not
clear the changes in DR6 because data breakpoints are not taken immediately after a
MOV SS,r/m or POP SS instruction. Due to this erratum, any DR6 changes caused by a
MOV SS,r/m or POP SS instruction may be cleared if the following instruction is a store.
Implication: When this erratum occurs, incorrect information may exist in DR6. This erratum will not
be observed under normal usage of the MOV SS,r/m or POP SS instructions (i.e.,
following them with an instruction that writes [e/r]SP). When debugging or when
developing debuggers, this behavior should be noted.
Workaround:None identified.
Status: For the steppings affected, see the Summary Tables of Changes.
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