Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 322

significant implemented physical address bit. In a processor that implements all
physical address bits, IMPL_PA_MSB is 62. Please see the processor-specific
documentation for further information on the number of physical address bits
implemented on the Itanium processor.
If unimplemented physical address bits are set by software, an Unimplemented Data
Address fault is raised during the TLB insert instructions (itc, itr). Inserts performed
by the VHPT walker, as noted in
unimplemented or reserved fields are used. For translations marked as Not-Present
(TLB.p is 0), the processor does not check the validity of PPN and some reserved bits as
noted in
When a processor model does not implement all physical address bits, the missing bits
are defined to be zero. Physical addresses in which bits
PA{62:min(IMPL_PA_MSB+1,62)} are not zero are considered "unimplemented"
physical addresses on that processor model. Physical addresses are checked for
correctness on use by ensuring that PA{62:min(IMPL_PA_MSB+1,62)} bits are zero.
4.3.2 Unimplemented Virtual Address Bits
As shown in
number (VRN), unimplemented and implemented bits.
Figure 4-19.
63 6160
VRN unimplemented
3 60 - IMPL_VA_MSB
All processor models provide three VRN bits in VA{63:61}. IMPL_VA_MSB is the
implementation-specific bit position of the most significant implemented virtual address
bit. In addition to the three VRN bits, all processor models implement at least 54 virtual
address bits; i.e., the smallest IMPL_VA_MSB is 53. In a processor that implements all
64 virtual address bits IMPL_VA_MSB is 60. Please see the processor-specific
documentation for further information on the number of virtual address bits
implemented on the Itanium processor.
If the PSR.vm bit is implemented, and if PSR.vm is 1, then virtual addresses are treated
as though one additional virtual address bit were unimplemented. If the PSR.vm bit is
implemented, at least 55 virtual address bits must be implemented.
When a processor model does not implement all virtual address bits, the missing bits
are defined to be a sign-extension of VA{IMPL_VA_MSB}. Virtual addresses in which
bits VA{60:min(IMPL_VA_MSB+1,60)} do not match VA{IMPL_VA_MSB} are
considered "unimplemented" virtual addresses on that processor model. Virtual
addresses are checked for correctness on use by ensuring that
VA{60:min(IMPL_VA_MSB+1,60)} bits are identical to VA{IMPL_VA_MSB}.
2:74
Figure 4-6.
Figure 4-19, a 64-bit virtual address consists of three fields: virtual region
Virtual Address Bit Fields
IMPL_VA_MSB
"VHPT Hashing" on page
implemented
IMPL_VA_MSB + 1
Volume 2, Part 1: Addressing and Protection
2:65, abort the VHPT search if
0