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20 Specification Update
HSD11. Performance Monitor Precise Instruction Retired Event May Present
Wrong Indications
Problem: When the PDIR (Precise Distribution for Instructions Retired) mechanism is activated
(INST_RETIRED.ALL (event C0H, umask value 00H) on Counter 1 programmed in PEBS
mode), the processor may return wrong PEBS/PMI interrupts and/or incorrect counter
values if the counter is reset with a SAV below 100 (Sample-After-Value is the counter
reset value software programs in MSR IA32_PMC1[47:0] in order to control interrupt
frequency).
Implication: Due to this erratum, when using low SAV values, the program may get incorrect PEBS
or PMI interrupts and/or an invalid counter state.
Workaround: The sampling driver should avoid using SAV<100.
Status: For the steppings affected, see the Summary Table of Changes.
HSD12. CR0.CD Is Ignored in VMX Operation
Problem: If CR0.CD=1, the MTRRs and PAT should be ignored and the UC memory type should
be used for all memory accesses. Due to this erratum, a logical processor in VMX
operation will operate as if CR0.CD=0 even if that bit is set to 1.
Implication: Algorithms that rely on cache disabling may not function properly in VMX operation.
Workaround: Algorithms that rely on cache disabling should not be executed in VMX root operation.
Status: For the steppings affected, see the Summary Table of Changes.
HSD13. Instruction Fetch May Cause Machine Check if Page Size and Memory
Type Was Changed Without Invalidation
Problem: This erratum may cause a machine-check error (IA32_MCi_STATUS.MCACOD=0150H)
on the fetch of an instruction that crosses a 4-KByte address boundary. It applies only
if (1) the 4-KByte linear region on which the instruction begins is originally translated
using a 4-KByte page with the WB memory type; (2) the paging structures are later
modified so that linear region is translated using a large page (2-MByte, 4-MByte, or 1-
GByte) with the UC memory type; and (3) the instruction fetch occurs after the paging-
structure modification but before software invalidates any TLB entries for the linear
region.
Implication: Due to this erratum an unexpected machine check with error code 0150H may occur,
possibly resulting in a shutdown. Intel has not observed this erratum with any
commercially available software.
Workaround: Software should not write to a paging-structure entry in a way that would change, for
any linear address, both the page size and the memory type. It can instead use the
following algorithm: first clear the P flag in the relevant paging-structure entry (e.g.,
PDE); then invalidate any translations for the affected linear addresses; and then
modify the relevant paging-structure entry to set the P flag and establish the new page
size and memory type.
Status: For the steppings affected, see the Summary Table of Changes.