Bits of
Word 40-7 8-31
Bits of
Word 5
MICVTMR
These bits are not used.
Real address of virtual-intervaHimer word (bits MICACF 0-7 Each of the] 1 functions of the expanded
virtual-machine assist can be activated only
when a specific bit in this group is one.
8 The functions of the shadow-table-bypass assist
can be activated only when this bit is one.
9-15 Each of the eight functions of the shadow
table-bypass assist can be activated only when
a specific bit in this group is one.
16- 31 These bits are not used.
Programming NotePlacing nonzero values in unused positions of
control register 6 or the parameter list is
inadvisable because these positions may be used
later and could cause incompatible execution.
Interaction of VM/370 Assists
Where the same virtual-machine instruction may be
executed by more than oneVM/370 assist, a fixed
order exists among the assists in which similar
functions are invoked. This order is (1) shadow
table-bypass assist, (2) virtual-machine assist, and
(3) expanded virtual-machine assist. Thus, for aSTORE THEN AND SYSTEM MASK instruction
for a virtual machine, theSTNSM function of the
shadow-table-bypass assist is invoked. That
function may (1) complete execution of the
instruction, (2) exit via a program interruption, or
(3) exit by invoking theSTNSM function of the
virtual-machine assist. The latter function may in
turn (1) complete execution of the instruction, (2)
exit via a program interruption, or (3) exit by
invoking theSTNSM function of the expanded
virtual-machine assist.
Similarly, a page-translation condition may
invoke the shadow-table-validation function of the
virtual-machine assist or the page-fault-reflection
function of the shadow-table-bypass assist if one of
those assists is installed. If both assists are
installed, the page-fault-reflection function of the
shadow-table-bypass assist is invoked first for apagE'-translation condition. This function may result in (1) a virtual-machine program
inlerruption, (2) a real-machine program
interruption, or (3) invocation of the shadow
table-validation function of the virtual-machine
assist.
Interaction of VM/370 Assists withOther Facilities
Control Mode
The virtual-machine assist and the shadow-table
bypass assist are defined to operate only on a CPU
which is in the EC mode.
Program-Event Recording
When any assist forVM/370 completely executes a
virtual-machine instruction, a program interruption
takes place in the real machine for PER events if
the real PER mask is one and in accordance with
the settings of the PER controls in real control
registers 9,10, and 11. Storage-alteration events
are indicated only for changes to virtual-machine
storage. Changes inVM/370 control blocks in real
storage are not indicated. However, a PER mask
of one in the real or virtual PSWs may cause a
virtual-machine-instruction assist function to exit
by taking a program interruption before completely
executing the instruction,The-- specific rules governing the effect of PER
mask values on the execution ofVM/370 assist
functions are:
1. ThePER indication is unpredictable for the
instructions of control-program assist.
2. A realPER mask value of one prevents a
virtual-machine external interruption for a
virtual interval-timer request.
3. A realPER mask value of one causes those
expanded -virtual-machine-assist functions
which can only partially execute a virtual
machine instruction to exit with a program
interruption for a privileged-operation
exception.
4. Load-PSW and supervisor-call functions of all
assists exit by a program interruption for a
privileged-operation exception or by a
supervisor-call interruption if thePER mask is tJle real pS.W, in the current virtual PSW, or in the new virtual PSW. 5. Set-system-mask, store-then-AND-system
mask, and store-then-OR-system mask
functions whose definition allows complete
execution under certain conditions exit with a
program interruption for a privileged-operation
exception if an attempt is made to change thePER mask in the virtual PSW. 6. Shadow-table validation and page-fault
reflection are inactive when the realPER mask
is one.
Assists forVM/3 70 5
Word 4
Bits of
Word 5
MICVTMR
These bits are not used.
Real address of virtual-intervaHimer word (bits
virtual-machine assist can be activated only
when a specific bit in this group is one.
8 The functions of the shadow-table-bypass assist
can be activated only when this bit is one.
9-15 Each of the eight functions of the shadow
table-bypass assist can be activated only when
a specific bit in this group is one.
16- 31 These bits are not used.
Programming Note
control register 6 or the parameter list is
inadvisable because these positions may be used
later and could cause incompatible execution.
Interaction of VM/370 Assists
Where the same virtual-machine instruction may be
executed by more than one
order exists among the assists in which similar
functions are invoked. This order is (1) shadow
table-bypass assist, (2) virtual-machine assist, and
(3) expanded virtual-machine assist. Thus, for a
for a virtual machine, the
shadow-table-bypass assist is invoked. That
function may (1) complete execution of the
instruction, (2) exit via a program interruption, or
(3) exit by invoking the
virtual-machine assist. The latter function may in
turn (1) complete execution of the instruction, (2)
exit via a program interruption, or (3) exit by
invoking the
virtual-machine assist.
Similarly, a page-translation condition may
invoke the shadow-table-validation function of the
virtual-machine assist or the page-fault-reflection
function of the shadow-table-bypass assist if one of
those assists is installed. If both assists are
installed, the page-fault-reflection function of the
shadow-table-bypass assist is invoked first for a
inlerruption, (2) a real-machine program
interruption, or (3) invocation of the shadow
table-validation function of the virtual-machine
assist.
Interaction of VM/370 Assists with
Control Mode
The virtual-machine assist and the shadow-table
bypass assist are defined to operate only on a CPU
which is in the EC mode.
Program-Event Recording
When any assist for
virtual-machine instruction, a program interruption
takes place in the real machine for PER events if
the real PER mask is one and in accordance with
the settings of the PER controls in real control
registers 9,
are indicated only for changes to virtual-machine
storage. Changes in
storage are not indicated. However, a PER mask
of one in the real or virtual PSWs may cause a
virtual-machine-instruction assist function to exit
by taking a program interruption before completely
executing the instruction,
mask values on the execution of
functions are:
1. The
instructions of control-program assist.
2. A real
virtual-machine external interruption for a
virtual interval-timer request.
3. A real
expanded -virtual-machine-assist functions
which can only partially execute a virtual
machine instruction to exit with a program
interruption for a privileged-operation
exception.
4. Load-PSW and supervisor-call functions of all
assists exit by a program interruption for a
privileged-operation exception or by a
supervisor-call interruption if the
mask, and store-then-OR-system mask
functions whose definition allows complete
execution under certain conditions exit with a
program interruption for a privileged-operation
exception if an attempt is made to change the
reflection are inactive when the real
is one.
Assists for