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Vol. 3 4-45
PAGING
(Any of the above steps would be skipped if the processor does not support the cache
in question.)
If the processor does not find a TLB or paging-structure-cache entry for the linear
address, it uses the linear address to traverse the entire paging-structure hierarchy,
as described in Section 4.3, Section 4.4.2, and Section 4.5.
4.10.2.3 Multiple Cached Entries for a Single Paging-Structure Entry
Note that multiple cached entries (in the paging-structure caches or TLBs) may
contain information derived from a single paging-structure entry. The following items
give some examples for IA-32e paging:
• Suppose that two PML4Es contain the same physical address and thus reference
the same page-directory-pointer table. Any PDPTE in that table may result in two
PDPTE-cache entries, each associated with a different set of linear addresses.
Specifically, suppose that the n
1
th
and n
2
th
entries in the PML4 table contain the
same physical address. This implies that the physical address in the m
th
PDPTE in
the page-directory-pointer table would appear in the PDPTE-cache entries
associated with both p
1
and p
2
, where (p
1
» 9) = n
1
, (p
2
» 9) = n
2
, and (p
1
&
1FFH) = (p
2
& 1FFH) = m. This is because both PDPTE-cache entries use the
same PDPTE, one resulting from a reference from the n
1
th
PML4E and one from
the n
2
th
PML4E.
• Suppose that the first PML4E (i.e., the one in position 0) contains the physical
address X in CR3 (the physical address of the PML4 table). This implies the
following:
— Any PML4-cache entry associated with linear addresses with 0 in bits 47:39
contains address X.
— Any PDPTE-cache entry associated with linear addresses with 0 in bits 47:30
contains address X. This is because the translation for a linear address for
which the value of bits 47:30 is 0 uses the value of bits 47:39 (0) to locate a
page-directory-pointer table at address X (the address of the PML4 table). It
then uses the value of bits 38:30 (also 0) to find address X again and to store
that address in the PDPTE-cache entry.
— Any PDE-cache entry associated with linear addresses with 0 in bits 47:21
contains address X for similar reasons.
— Any TLB entry for page number 0 (associated with linear addresses with 0 in
bits 47:12) translates to page frame X » 12 for similar reasons.
The same PML4E contributes its address X to all these cache entries because the
self-referencing nature of the entry causes it to be used as a PML4E, a PDPTE, a
PDE, and a PTE.