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    SubjectRe: chasing the four level page table
    Jon Smirl <> writes:

    > The DRM driver contains this routine:
    > drivers/char/drm/drm_memory.h
    > static inline unsigned long
    > drm_follow_page (void *vaddr)
    > {
    > pgd_t *pgd = pgd_offset_k((unsigned long) vaddr);
    > pud_t *pud = pud_offset(pgd, (unsigned long) vaddr);
    > pmd_t *pmd = pmd_offset(pud, (unsigned long) vaddr);
    > pte_t *ptep = pte_offset_kernel(pmd, (unsigned long) vaddr);
    > return pte_pfn(*ptep) << PAGE_SHIFT;
    > }
    > No other driver needs to chase the page table like this so there is
    > probably some other way to achieve this. Can someone who knows more
    > about the VM system tell me if there is a way to eliminate this code?

    Yes, you should use get_user_pages() instead if you access real memory.
    If you try to find hardware mappings using that there is no ready
    function for you right now, although I guess it could be added.

    The function is also not quite correct, it should already least take
    the page_table_lock (depending on where you call it from) and check
    p*_none() on each level.

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      Last update: 2005-03-22 14:09    [W:0.025 / U:9.088 seconds]
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