On Wed, May 28, 2008 at 7:11 PM, sahlot arvind <asahlot@xxxxxxxxx> wrote:
> I am working on Linux 2.6 and inside the init function of my module I am
> doing this -
>
> -------------
> init_module ()
> {
> va = kmalloc (4096, GFP_KERNEL);
> }
> --------------
>
> Now I want to read the page table entry for this va?
> What is the right way to do that?
> Thanks in advance
> - A
>
Actually, specifically for your question, the kernel is already doing
it - as I just found out :-)...and the answer is non-trivial:
Lookup in arch/x86/mm/fault.c:
static void dump_pagetable(unsigned long address)
{
#ifdef CONFIG_X86_32
__typeof__(pte_val(__pte(0))) page;
page = read_cr3();
page = ((__typeof__(page) *) __va(page))[address >> PGDIR_SHIFT];
#ifdef CONFIG_X86_PAE
printk("*pdpt = %016Lx ", page);
if ((page >> PAGE_SHIFT) < max_low_pfn
&& page & _PAGE_PRESENT) {
page &= PAGE_MASK;
page = ((__typeof__(page) *) __va(page))[(address >> PMD_SHIFT)
& (PTRS_PER_PMD - 1)];
printk(KERN_CONT "*pde = %016Lx ", page);
page &= ~_PAGE_NX;
}
#else
printk("*pde = %08lx ", page);
#endif
/*
* We must not directly access the pte in the highpte
* case if the page table is located in highmem.
* And let's rather not kmap-atomic the pte, just in case
* it's allocated already.
*/
if ((page >> PAGE_SHIFT) < max_low_pfn
&& (page & _PAGE_PRESENT)
&& !(page & _PAGE_PSE)) {
page &= PAGE_MASK;
page = ((__typeof__(page) *) __va(page))[(address >> PAGE_SHIFT)
& (PTRS_PER_PTE - 1)];
printk("*pte = %0*Lx ", sizeof(page)*2, (u64)page);
}
printk("\n");
#else /* CONFIG_X86_64 */
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
pgd = (pgd_t *)read_cr3();
pgd = __va((unsigned long)pgd & PHYSICAL_PAGE_MASK);
pgd += pgd_index(address);
if (bad_address(pgd)) goto bad;
printk("PGD %lx ", pgd_val(*pgd));
if (!pgd_present(*pgd)) goto ret;
pud = pud_offset(pgd, address);
if (bad_address(pud)) goto bad;
printk("PUD %lx ", pud_val(*pud));
if (!pud_present(*pud) || pud_large(*pud))
goto ret;
pmd = pmd_offset(pud, address);
if (bad_address(pmd)) goto bad;
printk("PMD %lx ", pmd_val(*pmd));
if (!pmd_present(*pmd) || pmd_large(*pmd)) goto ret;
pte = pte_offset_kernel(pmd, address);
if (bad_address(pte)) goto bad;
printk("PTE %lx", pte_val(*pte));
ret:
printk("\n");
return;
bad:
printk("BAD\n");
#endif
}
Well...it is non-trivial because the function catered for different
scenario - PAE or no PAE, 64/32 bit scnenario etc.
and within this same file, there are many instances / examples of
deriving the PTE from the kernel virtual address.
--
Regards,
Peter Teoh
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