Errata
24
Specification Update
BH26
PMI Request is Not Generated on a Counter Overflow if its OVF Bit is
Already Set in IA32_PERF_GLOBAL_STATUS
Problem:
If a performance counter overflows and software does not clear the corresponding
OVF (overflow) bit in IA32_PERF_GLOBAL_STATUS MSR (38Eh) then future overflows
of that counter will not trigger PMI (Performance Monitoring Interrupt) requests.
If software does not clear the OVF bit corresponding to a performance counter then future counter
overflows may not cause PMI requests.
Workaround:
Software should clear the IA32_PERF_GLOBAL_STATUS.OVF bit in the PMI handler.
Status:
For the steppings affected, see the Summary Tables of Changes.
BH27
Processor May Use an Incorrect Translation if the TLBs Contain Two
Different Translations For a Linear Address
Problem:
The TLBs may contain both ordinary and large-page translations for a 4-KByte range
of linear addresses. This may occur if software modifies a PDE (page-directory entry)
that is marked present to set the PS bit (this changes the page size used for the
address range). If the two translations differ with respect to page frame, permissions,
or memory type, the processor may use a page frame, permissions, or memory type
that corresponds to neither translation.
Due to this erratum, software may not function properly if it sets the PS flag in a PDE and also
changes the page frame, permissions, or memory type for the linear addresses
mapped through that PDE.
Workaround:
Software can avoid this problem by ensuring that the TLBs never contain both
ordinary and large-page translations for a linear address that differ with respect to
page frame, permissions, or memory type.
Status:
For the steppings affected, see the Summary Tables of Changes.
BH28
PEBS Record not Updated When in Probe Mode
Problem:
When a performance monitoring counter is configured for PEBS (Precise Event Based
Sampling), overflows of the counter can result in storage of a PEBS record in the PEBS
buffer. Due to this erratum, if the overflow occurs during probe mode, it may be
ignored and a new PEBS record may not be added to the PEBS buffer.
Implication:
Due to this erratum, the PEBS buffer may not be updated by overflows that occur
during probe mode.
Workaround:
None.
Status:
For the steppings affected, see the Summary Tables of Changes.
