mmu_notifers, pte_dirty questions

[Avi Kivity <avi@redhat.com>]

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