Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 585

11.7.4.1.2 Virtualization Cause Optimization
Virtualization cause optimization is enabled by the cause bit in the config_options
parameter of PAL_VP_INIT_ENV. When enabled, the causes of virtualization intercepts
will be provided to the VMM during PAL intercept handoffs within the virtual
environment. When disabled, no cause information will be provided during PAL
intercept handoffs.
This optimization requires no special synchronization.
11.7.4.1.3 Guest MOV-from-AR.ITC Optimization
Guest MOV-from-AR.ITC optimization allows software running with PSR.vm==1 to
execute MOV-from-AR.ITC instructions without any intercepts to the VMM. The value
returned will be the sum of the value in the interval timer counter register (ITC) and
interval timer offset register (ITO), unless a fault condition is detected (see
Table 11-25, "Behavior of Guest MOV-from-AR.ITC Instruction in Virtual Environment"
for details). The VMM is responsible for programming the ITO register to provide the
desired return value for guest execution with PSR.vm = 1 of the MOV-from-ITC
instruction when this optimization is enabled.
This optimization is enabled by the gitc bit in the config_options parameter of
PAL_VP_INIT_ENV. The behavior of the guest MOV-from-AR.ITC instruction is affected
by the settings of psr.ic and vpsr.ic as well, as shown in
This optimization requires no special synchronization.
This optimization is not supported on all processor implementations. Software can call
PAL_VP_ENV_INFO to determine the availability of this feature.
Table 11-25.Behavior of Guest MOV-from-AR.ITC Instruction in Virtual Envi-
a
gitc psr.si
0
1
a. gitc=0: Optimization disabled; gitc=1: Optimization enabled.
11.7.4.2 Virtualization Accelerations
Table 11-26
architecture.
Volume 2, Part 1: Processor Abstraction Layer
ronment
vpsr.si
0 0 No virtualization intercept – guest reads AR.ITC
0 1 Invalid setting – behavior is undefined.
1 0 Virtualization intercept
If vpsr.cpl is not zero: Privileged Register fault
1 1
If vpsr.cpl is zero: Virtualization intercept
0 0 No virtualization intercept – guest reads the sum of ITC and ITO
If vpsr.cpl is not zero: Privileged Register fault
0 1
If vpsr.cpl is zero: No Virtualization intercept – guest reads the sum of ITC and ITO
1 0 Virtualization intercept.
If vpsr.cpl is not zero: Privileged Register fault
1 1
If vpsr.cpl is zero: Virtualization intercept
summarizes the virtualization accelerations supported in Itanium
Table
MOV-from-AR.ITC when PSR.vm==1
11-25.
2:337