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4-42 Vol. 3
PAGING
— The value of the R/W flag of the PML4E.
— The value of the U/S flag of the PML4E.
— The value of the XD flag of the PML4E.
— The values of the PCD and PWT flags of the PML4E.
The following items detail how a processor may use the PML4 cache:
— If the processor has a PML4-cache entry for a linear address, it may use that
entry when translating the linear address (instead of the PML4E in memory).
— The processor does not create a PML4-cache entry unless the P flag is 1 and
all reserved bits are 0 in the PML4E in memory.
— The processor does not create a PML4-cache entry unless the accessed flag is
1 in the PML4E in memory; before caching a translation, the processor sets
the accessed flag if it is not already 1.
— The processor may create a PML4-cache entry even if there are no transla-
tions for any linear address that might use that entry (e.g., because the P
flags are 0 in all entries in the referenced page-directory-pointer table).
— If the processor creates a PML4-cache entry, the processor may retain it
unmodified even if software subsequently modifies the corresponding PML4E
in memory.
• PDPTE cache (IA-32e paging only).
1
Each PDPTE-cache entry is referenced by
an 18-bit value and is used for linear addresses for which bits 47:30 have that
value. The entry contains information from the PML4E and PDPTE used to
translate such linear addresses:
— The physical address from the PDPTE (the address of the page directory).
— The logical-AND of the R/W flags in the PML4E and the PDPTE.
— The logical-AND of the U/S flags in the PML4E and the PDPTE.
— The logical-OR of the XD flags in the PML4E and the PDPTE.
— The values of the PCD and PWT flags of the PDPTE.
The following items detail how a processor may use the PDPTE cache:
— If the processor has a PDPTE-cache entry for a linear address, it may use that
entry when translating the linear address (instead of the PML4E and the
PDPTE in memory).
— The processor does not create a PDPTE-cache entry unless the P flag is 1 and
the reserved bits are 0 in the PML4E and the PDPTE in memory.
— The processor does not create a PDPTE-cache entry unless the accessed flags
are 1 in the PML4E and the PDPTE in memory; before caching a translation,
the processor sets any accessed flags that are not already 1.
1. With PAE paging, the PDPTEs are stored in internal, non-architectural registers. The operation of
these registers is described in Section 4.4.1 and differs from that described here.