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CHAPTER 4 MEMORY MANAGEMENT SYSTEM
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(f) xkuseg (64-bit Kernel mode, user space)
When KX = 1 in the Status register and bits 63 and 62 of the virtual address space are 00, the xkuseg
virtual address space is selected; it is the current user address space. The virtual address is extended
with the contents of the 8-bit ASID field to form a unique virtual address.
If the ERL bit of the Status register is 1, the user address space is assigned 2 Gbytes (2
becomes unmapped (with virtual addresses being used as physical addresses) and uncached so that
the cache error handler can use it. This allows the Cache Error exception code to operate uncached
using r0 as a base register.
31
bytes) and
(g) xksseg (64-bit Kernel mode, current supervisor space)
When KX = 1 in the Status register and bits 63 and 62 of the virtual address space are 01, the xksseg
address space is selected; it is the current supervisor address space. The virtual address is extended
with the contents of the 8-bit ASID field to form a unique virtual address.
(h) xkphys (64-bit Kernel mode, physical spaces)
When the KX = 1 in the Status register and bits 63 and 62 of the virtual address space are 10, the
virtual address space is called xkphys and selected as either cached or uncached. If any of bits 58 to
32 of the address is 1, an attempt to access that address results in an address error.
Table 4-5. Cacheability and the xkphys Address Space
Bits 61-59
Cacheability
Start address
0
Cached
0x8000 0000 0000 0000
1
Cached
0x8800 0000 0000 0000
2
Uncached
0x9000 0000 0000 0000
3
Cached
0x9800 0000 0000 0000
4
Cached
0xA000 0000 0000 0000
5
Cached
0xA800 0000 0000 0000
6
Cached
0xB000 0000 0000 0000
7
Cached
0xB800 0000 0000 0000
(i) xkseg (64-bit Kernel mode, physical spaces)
When the KX = 1 in the Status register and bits 63 and 62 of the virtual address space are 11, the
virtual address space is called xkseg and selected as either of the following:
λ
kernel virtual space, xkseg, the current kernel virtual space; the virtual address is extended
with the contents of the 8-bit ASID field to form a unique virtual address
one of the four 32-bit kernel compatibility spaces, as described in the next section.
λ