IA32 Page Tables

1
IA32 Page Tables
2
Why Virtual Memory

• Users point of view
• protection
• encapsulation / transparency
• resource independence
• Systems point of view
• protection
• user control
• resource control

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What is Virtual Memory?

• A mapping
• virtual address physical address
• 32 bit 32 bit
• 4G contiguous 4G arbitrary, incl. nil
• page granular, access controlled

4
What is Virtual Memory?

• multiple mappings
• virtual address physical address
• 32 bit 32 bit
• 4G contiguous 4G arbitrary, incl. nil
• page granular, access controlled

5
What is Virtual Memory?

• multiple mappings
• virtual address physical address
• 32 bit 32 bit
• 4G contiguous 4G arbitrary, incl. nil
• page granular, access controlled

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x86 Page Tables
7
x86 Page Tables
virtual address
8
x86 Page Tables
virtual address
CR3
9
x86 Page Tables
virtual address
31 22
CR3
10
x86 Page Tables
virtual address
31 22
CR3
11
x86 Page Tables
virtual address
CR3
12
x86 Page Tables
virtual address
21 12
CR3
13
x86 Page Tables
virtual address
11 0
CR3
14
x86 Page Tables
virtual address
11 0
CR3
15
Multi-Level Page Table
16
Linear Page Table
31 12
17
Linear Page Table
31 12
18
Linear Page Table
31 12
19
Inverted Page Table
31 12
hash
20
Inverted Page Table
31 12
hash

21
Hasheded Page Table
31 12
hash
22
Hasheded Page Table
31 12
hash

23
Hasheded Page Table
31 12
hash

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Page Tables

• Trees
• MPT (e.g. x86)
• LPT (e.g. Mips/Alpha)
• Hash Tables
• IPT (John Cocke)
• HPT (Jerry Huck, Jim Hayes)
• Special Solutions
• Clustered PTs
• Guarded PTs

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Pros Cons

• MPT
• IPT
• HPT

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Pros Cons

• MPT
• grouping, regions
• sharing
• IPT
• sparsity
• HPT
• sparsity
• sharing

• low sparsity
• high startup costs
• no grouping
• no sharing
• HT / memory size
• needs segmentation

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HPT - Multiple Address Spaces
232
232
A
A
232
B
C
28
HPT - Multiple Address Spaces
232
252
A
232
A
A
232
B
B
C
C
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x86 Page Tables
CR3
4K
4K
4K
30
x86 Page Tables
CR3
4K
4K
4K
4M
31
x86 PT entries
31 pointer 12
p
w
u
0
1 present
1 writable
1 user acc
32
x86 PT entries
31 pointer 12
p
w
u
wt
cd
0
1 present
1 writable
1 user acc
33
x86 PT entries
31 pointer 12
p
w
u
wt
cd
a
d
0
1 present
1 writable
1 user acc
34
x86 PT entries
31 pointer 12
p
w
u
wt
cd
a
d
0
g
1 present
1 writable
1 user acc
1 TLB-global
35
x86 PT entries
31 pointer 12
p
w
u
wt
cd
a
d
0
g
1 present
1 writable
1 user acc
1 TLB-global
31 pointer 22
p
w
u
wt
cd
a
d
1
g
0000000000