Memory Management Unit
e200z3 Power Architecture Core Reference Manual, Rev. 2
5-6
Freescale Semiconductor
On a TLB hit, the generation of the physical address occurs as shown in
5.2.5
Permissions
An operating system may restrict access to virtual pages by selectively granting permissions for user-mode
read, write, and execute, and supervisor-mode read, write, and execute on a per-page basis. These
permissions can be set up for a particular system (for example, program code may be execute only, and
data structures may be mapped as read/write/no-execute) and be changed by the operating system based
on application requests and operating system policies.
The UX, SX, UW, SW, UR, and SR access control bits are provided to support selective permissions
(access control):
•
SR—Supervisor read permission. Allows loads and load-type cache management instructions to
access the page while in supervisor mode (MSR[PR = 0]).
•
SW—Supervisor write permission. Allows stores and store-type cache management instructions to
access the page while in supervisor mode (MSR[PR = 0]).
•
SX—Supervisor execute permission. Allows instruction fetches to access the page and instructions
to be executed from the page while in supervisor mode (MSR[PR = 0]).
•
UR—User read permission. Allows loads and load-type cache management instructions to access
the page while in user mode (MSR[PR = 1]).
•
UW—User write permission. Allows stores and store-type cache management instructions to
access the page while in user mode (MSR[PR = 1]).
•
UX—User execute permission. Allows instruction fetches to access the page and instructions to be
executed from the page while in user mode (MSR[PR = 1]).
If the translation match was successful, the permission bits are checked as shown in
. If the
access is not allowed by the access permission mechanism, the processor generates an instruction or data
storage interrupt (ISI or DSI).
0b0111
16 Mbytes
EA[32–39] = EPN[32–39]?
0b1000
64 Mbytes
EA[32–37] = EPN[32–37]?
0b1001
256 Mbytes
EA[32–35] = EPN[32–35]?
Table 5-2. Page Size (for e200z3 Core) and EPN Field Comparison (continued)
SIZE Field
Page Size
(4
SIZE
Kbytes)
EA to EPN Comparison
(Bits 32–53; 2
×
SIZE)
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