Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3, Manual

Page: 310 / 1898

2:62 Volume 2, Part 1: Addressing and Protection
The processor does not manage the VHPT or perform any writes into the table.
Software is responsible for insertion of entries into the VHPT (including replacement
algorithms), dirty/access bit updates, invalidation due to purges and coherency in a
multiprocessor system. The processor does not ensure the TLBs are coherent with the
VHPT memory image.
If software needs to control the entries inserted into the TLB more explicitly, or
programs the VHPT with differing mappings for the same virtual address range, it may
need to take additional action to ensure forward progress.
See “VHPT Searching” on
page 2:62.
4.1.5.1 VHPT Configuration
The Page Table Address (PTA) register determines whether the processor is enabled to
walk the VHPT, anchors the VHPT in the virtual address space, and controls VHPT size
and configuration information. The VHPT can be configured as either a per-region
virtual linear page table structure (8-byte short format) or as a single large hash page
table (32-byte long format). No mixing of formats is allowed within the VHPT.
To implement a per-region linear page table structure an operating system would
typically map the leaf page table nodes with small backing virtual translations. The size
of the table is expanded to include all possible virtual mappings, effectively creating a
large per-region flat page table within the virtual address space.
To implement a single large hash page table, the entire VHPT is typically mapped with a
single large pinned virtual translation placed in the translation registers and the size of
the table is reduced such that only a subset of all virtual mappings can be resident
within the table. Operating systems can tune the size of the hash page table based on
the size of physical memory and operating system performance requirements.
4.1.5.2 VHPT Searching
When enabled, the processor’s VHPT walker searches the VHPT for a translation after a
failed instruction or data TLB search. The VHPT walker checks only the specific VHPT
entry addressed by the short- or the long-format hash function, as selected by PTA.vf.
If additional TLB misses are encountered during the VHPT access, a VHPT Translation
Figure 4-9. Virtual Hash Page Table (VHPT)
TLB
Virtual Address
Hashing
Function
VHPT
Optional Collision Search Chain
Optional Operating System Page Tables
Region
Registers
rid
vpn
PTA
2
PTA.size
PTA.base
ps
TC
Install