如何从 Linux kernel 模块中的逻辑地址获取物理地址？

Question

Is there any suitable way to get the physical address by the logical one except to walk through page directory entries by hand? I've looked for this functionality in kernel's sources and found that there is a follow_page function that do it well with built-in huge and transparent-huge pages support. But it's not exported to kernel modules (why???)...

So, I don't want to invent the wheel and I think that it's not very good to reimplement the follow_page functionality by hand.

Answer 1

Well, it might looks as something like that (follow PTE from an virtual address):

void follow_pte(struct mm_struct * mm, unsigned long address, pte_t * entry)
{
    pgd_t * pgd = pgd_offset(mm, address);

    printk("follow_pte() for %lx\n", address);

    entry->pte = 0;
    if (!pgd_none(*pgd) && !pgd_bad(*pgd)) {
        pud_t * pud = pud_offset(pgd, address);
        struct vm_area_struct * vma = find_vma(mm, address);

        printk(" pgd = %lx\n", pgd_val(*pgd));

        if (pud_none(*pud)) {
            printk("  pud = empty\n");
            return;
        }
        if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
            entry->pte = pud_val(*pud);
            printk("  pud = huge\n");
            return;
        }

        if (!pud_bad(*pud)) {
            pmd_t * pmd = pmd_offset(pud, address);

            printk("  pud = %lx\n", pud_val(*pud));

            if (pmd_none(*pmd)) {
                printk("   pmd = empty\n");
                return;
            }
            if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
                entry->pte = pmd_val(*pmd);
                printk("   pmd = huge\n");
                return;
            }
            if (pmd_trans_huge(*pmd)) {
                entry->pte = pmd_val(*pmd);
                printk("   pmd = trans_huge\n");
                return;
            }
            if (!pmd_bad(*pmd)) {
                pte_t * pte = pte_offset_map(pmd, address);

                printk("   pmd = %lx\n", pmd_val(*pmd));

                if (!pte_none(*pte)) {
                    entry->pte = pte_val(*pte);
                    printk("    pte = %lx\n", pte_val(*pte));
                } else {
                    printk("    pte = empty\n");
                }
                pte_unmap(pte);
            }
        }
    }
}

Answer 2

I think you can achieve virtual->physical translation through an indirect method by a combination of /proc/[pid]/maps ( gives the virtual mapping for a process ) and /proc/[pid]/pagemap ( Gives Virtual Page to Physical Page mapping for every addressable page ). First, find out the mapping of virtual addresses of your process from maps ( This is done so that you don't search every byte in pagemap ) Then check for the physical mapping of the desired virtual address in pagemap ( pagemap is not in text format. Here is a detailed explantion of the format Pagemap ) This should give you the exact virtual-->physical mapping

Answer 3

It sounds like you're looking for virt_to_phys .