mmu_notifers, pte_dirty questions

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Why no notifer when testing and clearing the dirty bit?

(*clear_flush_dirty)(...).

static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
                unsigned long address)
{
    struct mm_struct *mm = vma->vm_mm;
    pte_t *pte;
    spinlock_t *ptl;
    int ret = 0;

    pte = page_check_address(page, mm, address, &ptl, 1);
    if (!pte)
        goto out;

    if (pte_dirty(*pte) || pte_write(*pte)) {
        pte_t entry;

        flush_cache_page(vma, address, pte_pfn(*pte));
        entry = ptep_clear_flush_notify(vma, address, pte);
        entry = pte_wrprotect(entry);
        entry = pte_mkclean(entry);
        set_pte_at(mm, address, pte, entry);

set_pte_at_notify()? without this (or clear_flush_dirty) Linux will assume all ptes are now clean; if the guest writes to a page nothing will catch it.

-> with set_pte_at_notify(), we can drop the spte and mark the page as dirty, so the next write will re-instantiate the spte -> with ->clear_flush_dirty(), we can track the dirty state without dropping the spte.

        ret = 1;
    }

    pte_unmap_unlock(pte, ptl);
out:
    return ret;

I'm probably missing something big as I can't see how this works.

--
error compiling committee.c: too many arguments to function

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