I have written following code to understand the Linux page table data
structures. It tries to read data at a virtual address
asm("movl %%cr3, %0":"=r" (pgd_base));
printk("pgd_base = %#lx\n", pgd_base);
pmd_base = *(unsigned long*)__va((pgd_base + ((vaddr & PGDIR_MASK) >>
PGDIR_SHIFT)));
printk("pmd_base = %#lx\n", pmd_base);
pte_base = *(unsigned long*)__va((pmd_base + ((vaddr & PMD_MASK) >>
PMD_SHIFT)));
printk("pte_base = %#lx\n", pte_base);
page_frame_base = *(unsigned long*)__va((pte_base + ((vaddr &
PAGE_MASK) >> PAGE_SHIFT)));
printk("page_frame_base = %#lx\n", page_frame_base);
value = *(unsigned int*)__va((page_frame_base + (vaddr & ~PAGE_MASK)));
I get pmd_base as NULL. Can someone explain me why?
Also the vaddr is address of an integer in an application. And I have
mlock'ed it before passing the virtual address as follows:
mlock(&val, sizeof(int));
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