Specification Update
23
•
UC the data size of each write will now always be 8 bytes, as opposed to the original
data size.
•
WP the data size of each write will now always be 8 bytes, as opposed to the original
data size and there may be a memory ordering violation.
•
WT there may be a memory ordering violation.
Workaround:
Software should avoid crossing page boundaries from WB or WC memory type to UC,
WP or WT memory type within a single REP MOVS or REP STOS instruction that will
execute with fast strings enabled.
Status:
For the steppings affected, see the Summary Tables of Changes.
BJ26.
Reported Memory Type May Not Be Used to Access the VMCS and
Referenced Data Structures
Problem:
Bits 53:50 of the IA32_VMX_BASIC MSR report the memory type that the processor
uses to access the VMCS and data structures referenced by pointers in the VMCS. Due
to this erratum, a VMX access to the VMCS or referenced data structures will instead
use the memory type that the MTRRs (memory-type range registers) specify for the
physical address of the access.
Implication:
Bits 53:50 of the IA32_VMX_BASIC MSR report that the WB (write-back) memory type
will be used but the processor may use a different memory type.
Workaround:
Software should ensure that the VMCS and referenced data structures are located at
physical addresses that are mapped to WB memory type by the MTRRs.
Status:
For the steppings affected, see the Summary Tables of Changes.
BJ27.
Single Step Interrupts with Floating Point Exception Pending May Be
Mishandled
Problem:
In certain circumstances, when a floating point exception (#MF) is pending during
single-step execution, processing of the single-step debug exception (#DB) may be
mishandled.
Implication:
When this erratum occurs, #DB will be incorrectly handled as follows:
•
#DB is signaled before the pending higher priority #MF (Interrupt 16)
•
#DB is generated twice on the same instruction
Workaround:
None identified
Status:
For the steppings affected, see the Summary Tables of Changes.
BJ28.
Storage of PEBS Record Delayed Following Execution of MOV SS or STI
Problem:
When a performance monitoring counter is configured for PEBS (Precise Event Based
Sampling), overflow of the counter results in storage of a PEBS record in the PEBS
buffer. The information in the PEBS record represents the state of the next instruction
to be executed following the counter overflow. Due to this erratum, if the counter
overflow occurs after execution of either MOV SS or STI, storage of the PEBS record is
delayed by one instruction.
Implication:
When this erratum occurs, software may observe storage of the PEBS record being
delayed by one instruction following execution of MOV SS or STI. The state information
in the PEBS record will also reflect the one instruction delay.
Workaround:
None identified
Status:
For the steppings affected, see the Summary Tables of Changes.
