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        write_cr3(KA2PA(dba));
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        write_cr3(KA2PA(dba));
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    }
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    }
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    paging_on();
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    paging_on();
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}
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}
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/*
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 * Besides mapping pages to frames, this function also sets the present bit of
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 * the page's specifier in both page directory and respective page table. If
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 * the page table for this page has not been allocated so far, it will take
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 * care of it and allocate the necessary frame.
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 *
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 * PAGE_CACHEABLE flag: when set, it turns caches for that page on
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 * PAGE_NOT_PRESENT flag: when set, it marks the page not present
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 * PAGE_USER flag: when set, the page is accessible from userspace
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 *
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 * When the root parameter is non-zero, it is used as the page directory address.
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 * Otherwise, the page directory address is read from CPU.
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 */
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void map_page_to_frame(__address page, __address frame, int flags, __address root)
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{
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    struct page_specifier *pd, *pt;
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    __address dba, newpt;
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    int pde, pte;
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    if (root) dba = root;
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    else dba = read_cr3();
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    pde = page >> 22;       /* page directory entry */
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    pte = (page >> 12) & 0x3ff; /* page table entry */
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    pd = (struct page_specifier *) PA2KA(dba);
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    if (!pd[pde].present) {
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        /*
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         * There is currently no page table for this address. Allocate
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         * frame for the page table and clean it.
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         */
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        newpt = frame_alloc(FRAME_KA);
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        pd[pde].frame_address = KA2PA(newpt) >> 12;
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        memsetb(newpt, PAGE_SIZE, 0);
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        pd[pde].present = 1;
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        pd[pde].uaccessible = 1;
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    }
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    pt = (struct page_specifier *) PA2KA((pd[pde].frame_address << 12));
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    pt[pte].frame_address = frame >> 12;
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    pt[pte].present = !(flags & PAGE_NOT_PRESENT);
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    pt[pte].page_cache_disable = !(flags & PAGE_CACHEABLE);
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    pt[pte].uaccessible = (flags & PAGE_USER) != 0;
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    pt[pte].writeable = (flags & PAGE_WRITE) != 0; 
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}
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