Specification Update 35
BU48. 64-bit REP MOVSB/STOSB May Clear The Upper 32-bits of RCX, RDI And RSI Before Any Data is Transferred
Problem: If a REP MOVSB/STOSB is executed in 64-bit mode with an address size of 32 bits, and
if an interrupt is being recognized at the start of the instruction operation, the upper
32-bits of RCX, RDI and RSI may be cleared, even though no data has yet been copied
or written.
Implication: Due to this erratum, the upper 32-bits of RCX, RDI and RSI may be prematurely
cleared.
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.
BU49. An Interrupt Recognized Prior to First Iteration of REP MOVSB/STOSB May Result EFLAGS.RF Being Incorrectly Set
Problem: If a REP MOVSB/STOSB is executed and an interrupt is recognized prior to completion
of the first iteration of the string operation, EFLAGS may be saved with RF=1 even
though no data has been copied or stored. The Software Developer’s Manual states that
RF will be set to 1 for such interrupt conditions only after the first iteration is complete.
Implication: Software may not operate correctly if it relies on the value saved for EFLAGS.RF when
an interrupt is recognized prior to the first iteration of a string instruction. Debug
exceptions due to instruction breakpoints are delivered correctly despite this erratum;
this is because the erratum occurs only after the processor has evaluated instruction-
breakpoint conditions.
Workaround: Software whose correctness depends on value saved for EFLAGS.RF by delivery of the
affected interrupts can disable fast-string operation by clearing Fast-String Enable in bit
0 in the IA32_MISC_ENABLE MSR (1A0H).
Status: For the steppings affected, see the Summary Tables of Changes.
BU50. Accessing Physical Memory Space 0-640K through the Graphics Aperture May Cause Unpredictable System Behavior
Problem: The physical memory space 0-640K when accessed through the graphics aperture may
result in a failure for writes to complete or reads to return incorrect results.
Implication: A hang or functional failure may occur during graphics operation such as OGL or OCL
conformance tests, 2D/3D games and graphics intensive application.
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.
BU51. PEBS May Unexpectedly Signal a PMI After The PEBS Buffer is Full
Problem: The Software Developer’s Manual states that no PMI should be generated when PEBS
index reaches PEBS Absolute Maximum. Due to this erratum, a PMI may be generated
even though the PEBS buffer is full.
Implication: PEBS may trigger a PMI even though the PEBS index has reached the PEBS Absolute
Maximum.
Workaround: None identified.
Status: For the steppings affected, see the Summary Tables of Changes.