Mobile Intel Pentium 4 Processor with 533 MHz System Bus Specification Update

R
24 Specification Update
Z28.
Changes to CR3 Register do not Fence Pending Instruction Page Walks
Problem: When software writes to the CR3 register, it is expected that all previous/outstanding code, data accesses
and page walks are completed using the previous value in CR3 register. Due to this erratum, it is
possible that a pending instruction page walk is still in progress, resulting in an access (to the PDE
portion of the page table) that may be directed to an incorrect memory address.
Implication: The results of the access to the PDE will not be consumed by the processor so the return of incorrect
data is benign. However, the system may hang if the access to the PDE does not complete with data (e.g.
infinite number of retries).
Workaround: It is possible for the BIOS to have a workaround for this erratum.
Status: For the steppings affected, see the Summary Tables of Changes.
Z29.
Simultaneous Page Faults at Similar Page Offsets on Both Logical Processors
of a Hyper-Threading Technology Enabled Processor May Cause Application
Failure
Problem: An incorrect value of CR2 may be presented to one of the logical processors of an HT Technology
enabled processor if a page access fault is encountered on one logical processor in the same clock cycle
that the other logical processor also encounters a page fault. Both accesses must cross the same 4 byte
aligned offset for this erratum to occur. Only a small percentage of such simultaneous accesses are
vulnerable. The vulnerability of the alignment for any given fault is dependent on the state of other
circuitry in the processor. Additionally, a third fault from an access that occurs sequentially after one of
these simultaneous faults has to be pending at the time of the simultaneous faults. This erratum is caused
by a one-cycle hole in the logic that controls the timing by which a logical processor is allowed to access
an internal asynchronous fault address register. The end result is that the value of CR2 presented to one
logical processor may be corrupted.
Implication: The operating system is likely to terminate the application that generated an incorrect value of CR2.
Workaround: An operating system or page management software can significantly reduce the already small
possibility of encountering this failure by restarting or retrying the faulting instruction and only
terminate the application on a subsequent failures of the same instruction. It is possible for BIOS to
contain a workaround for this erratum.
Status: For the steppings affected, see the Summary Tables of Changes.