CODEWITHSUNDEEP
linux-kernelarmmmu
AnshuMan Gupta
AnshuMan Gupta

Reputation: 333

page table walk in armv7 linux by S/W leads to which version of page table ARM PTE or Linux PTE

My question is in handle_mm_fault function or any S/W page table walk.

pgd = pgd_offset(mm,address);
pud = pud_offset (pgd,address);
pmd = pmd_offset (pud,address);
pte = pte_offset_map(pmd,address);

Will the final computed pte be the ARM or LINUX version?

In armv7 supports 2 levels of page table; At the first level 4096 entries of each 4 bytes has an address for the second level. The second level has 256 entries of each 4 bytes. Linux has tweaked the page table to have 2048 entries of each 8 bytes in other words having two pointers to second level of page table having 512 entries placed contiguously. Linux PTE stored below these 512 ARM PTE.

So I understand that page table walk through in S/W will leads to ARM PTE only, but that is not correct Linux always operates on Linux PTEs?

Please tell me where I am wrong?

I Got the answer. I understood that, all these macro will leads to the Linux PTE only , since the L2 level page table of 4kb size and from 0th offset the linux pte0 starts and 1024th offset linux pte1 starts. while calculating pte_index it mask the lower 12 bits of PMD value thus PMD will always point to the start of page and there are Linux PTE stored.

Upvotes: 0

Views: 448

Answers (1)

AnshuMan Gupta
AnshuMan Gupta

Reputation: 333

I Got the answer. I understood that, all these macro will leads to the Linux PTE only , since the L2 level page table of 4kb size and from 0th offset the linux pte0 starts and 1024th offset linux pte1 starts. while calculating pte_index it mask the lower 12 bits of PMD value thus PMD will always point to the start of page and there are Linux PTE stored.

Upvotes: 0

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