30:31 Z15 I See the description of
ZOo
Setting ZPR[Zn] = 00 for a ZPR field is the only way to deny read access to a page defined by an
otherwise valid TLB entry. TLB_entry[EX] and TLB_entry[WR] do not support read protection. Note
that the
icbi
instruction is considered a load with respect to access protection; executed in user
mode, it causes a data storage interrupt if MSR[DR] = 1 and ZPR[Zn] = 00 is associated with the EA.
For a given
ZPR field value, a program
in
supervisor state always has equal or greater access than a
program
in
the problem state. System software can never be denied read (load) access for a valid
TLB entry.
6.7.2 Access Protection
for
Cache Control Instructions
Architecturally the instructions dcba,
dcbi,
and
dcbz
are treated as "stores" because they can
change data, or cause loss of data by invalidating a dirty line
(a
modified cache block).
Table 6-2 summarizes the conditions under which the cache control instructions can cause data
storage interrupts.
Table 6-2.
Protection
Applied
to
Cache
Control
Instructions
Possible Data Storage
interrupt
Instruction
When ZPR[Zn] = 00 When TLB_entry[WR] = 0
dcba
No
(instruction no-ops) No (instruction no-ops)
dcbf
Yes
No
dcbi
No
Yes
dcbst
Yes
No
dcbt
No
(instruction no-ops)
No
dcbtst
No
(instruction no-ops)
No
dcbz
Yes
Yes
dccci
No
Yes
dcread
No
No
icbi
Yes
No
icbt
No
No
iccci
No
No
icread
No
No
If data address translation is enabled, and write permission is denied (TLB_entry[WR] =
a),
dcbi
and
dcbz
can cause data storage interrupts.
dcbz
can cause a data storage interrupt when executed
in
the problem state and all access is denied (ZPR[Zn] = 00);
dcbi
cannot cause a data storage interrupt
because it is a privileged instruction.
The
dcba
instruction enables "speculative" line establishment
in
the cache arrays; the established
lines do not cause a line fill. Because the effects of
dcba
are speculative, interrupts that would
otherwise result when
ZPR[Zn] = 00 or TLB_entry[WR] = a do not occur.
In
such cases,
dcba
is
treated as a no-op.
Preliminary Memory Management
6-15
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