Hi,

?? 2. how can i change the page permisson before write back instruction?of
user mode application?
????? for example, find out the page tables of current application, find out
the pte which represents
the instruction that generate data abort, then modify pte, write back
instruction, restore pte, done.
??? how to do these?

I think you can get the pgd of this process by current->mm->pgd and
pgd_offset macro to ge the pgd entry for that address. There are
macros available for accessing pmd and pte too. For example
pte_offset_map for pte and a locking version for the same is also
there. I don't have any hands on experience on this,  so our kernel
experts can comment on this more.

And one more thing, if you can look at the function handle_mm_fault
(mm/memory.c), there are plenty of refererces for accesing these page
table entries.

With Regards,
Subin K G

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With Regards
Subin Gangadharan

I am not afraid and I am also not afraid of being afraid.