1. Recursive Page Table Lookup in the x86
CSCE 410/611
Recursive Page Table Lookup in the x86
How to access PDEs and PTEs in virtual memory?
RECAP: Address Translation in the x86
Accessing PTEs and PDEs?
Addressing a PTE using RPTL
Addressing a PDE using RPTL
Recursive Page Table Lookup

2. RECAP: Logical Address Translation in x86
CSCE 410/611
RECAP: Logical Address Translation in x86
CPU
X (10bit)
X (10bit)
Y (10bit)
Y (10bit)
D (12bit)
D (12bit)
PTBR
page directory X
PDE
page table page Y
frame in phys. memory
PTE D
mem loc
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

3. Accessing PTEs and PDEs?!
CSCE 410/611
Accessing PTEs and PDEs?!
CPU
X (10bit)
?!?!
FPTP (20bit)
Y (10bit)
?!?!
D (12bit)
Y (10bit) 00
Phys. Address of entry: FPTP | Y | 00
PTBR
page directory X
FPTP
CPU issues logical addresses!!
PDE
FPTP
page table page Y
frame in phys. memory
PTE D
Modify this entry?!
mem loc
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

4. Addressing a PTE using Recursive Table Lookup
CSCE 410/611
Addressing a PTE using Recursive Table Lookup
CPU
X(10bit)
Y (10bit)
1023 (10bit)
1023 (10bit)
X (10bit)
X (10bit)
Y (10bit)
Y (10bit) 00 00
PTBR
FPD
page directory
FPTP
FPDP
page table page
1023
PTE
PTE
FPD
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

5. Addressing a PTE using Recursive Table Lookup
CSCE 410/611
Addressing a PTE using Recursive Table Lookup
CPU
X(10bit)
Y (10bit)
1023 (10bit)
1023 (10bit)
X (10bit)
Y (10bit) 00
PTBR
FPD
page directory
FPTP
FPDP
page table page
1023
PTE
PTE
FPD
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

6. Addressing a PTE using Recursive Table Lookup
CSCE 410/611
Addressing a PTE using Recursive Table Lookup
CPU
X(10bit)
Y (10bit)
1023 (10bit)
1023 (10bit)
X (10bit)
X (10bit)
Y (10bit) 00
PTBR
FPD
page directory X
FPTP
FPDP
page table page
1023
PTE
PTE
FPD
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

7. Addressing a PTE using Recursive Table Lookup
CSCE 410/611
Addressing a PTE using Recursive Table Lookup
CPU
X(10bit)
Y (10bit)
1023 (10bit)
1023 (10bit)
X (10bit)
X (10bit)
Y (10bit)
Y (10bit) 00 00
PTBR
FPD
page directory X
FPTP
FPDP
page table page
1023
Y*4
frame in phys. memory
PTE
PTE
FPD
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

8. Addressing a PDE using Recursive Table Lookup
CSCE 410/611
Addressing a PDE using Recursive Table Lookup
CPU
X(10bit)
1023 (10bit)
1023 (10bit)
X (10bit) 00
PTBR
FPD
PDE
PDE
1023
1023
FPD
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

9. Addressing a PDE using Recursive Table Lookup
CSCE 410/611
Addressing a PDE using Recursive Table Lookup
CPU
X(10bit)
1023 (10bit)
1023 (10bit)
1023 (10bit)
X (10bit) 00
PTBR
FPD
PDE
PDE
1023
1023
FPD
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

10. Addressing a PDE using Recursive Table Lookup
CSCE 410/611
Addressing a PDE using Recursive Table Lookup
CPU
X(10bit)
1023 (10bit)
1023 (10bit)
1023 (10bit)
1023 (10bit)
X (10bit) 00
PTBR
FPD
PDE
PDE
1023
1023
FPD
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

11. Addressing a PDE using Recursive Table Lookup
CSCE 410/611
Addressing a PDE using Recursive Table Lookup
CPU
X(10bit)
1023 (10bit)
1023 (10bit)
1023 (10bit)
1023 (10bit)
X (10bit)
X (10bit) 00 00
PTBR
FPD
X*4
PDE
PDE
1023
1023
FPD
Mantra: “PDE => PTE => Memory Location”
Recursive Page Table Lookup

12. Memory Usage of Recursive Table Lookup
CSCE 410/611
Memory Usage of Recursive Table Lookup
logical
address space
FPD
page table
4MB
Page Directory
Recursive Page Table Lookup