On Thu, Jun 15, 2023 at 07:11:41PM +0500, Muhammad Usama Anjum wrote:
> +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
> + unsigned long end, struct mm_walk *walk)
> +{
> + bool is_written, flush = false, is_interesting = true;
> + struct pagemap_scan_private *p = walk->private;
> + struct vm_area_struct *vma = walk->vma;
> + unsigned long bitmap, addr = end;
> + pte_t *pte, *orig_pte, ptent;
> + spinlock_t *ptl;
> + int ret = 0;
> +
> + arch_enter_lazy_mmu_mode();
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> + ptl = pmd_trans_huge_lock(pmd, vma);
> + if (ptl) {
> + unsigned long n_pages = (end - start)/PAGE_SIZE;
> +
> + if (p->max_pages && n_pages > p->max_pages - p->found_pages)
> + n_pages = p->max_pages - p->found_pages;
> +
> + is_written = !is_pmd_uffd_wp(*pmd);
> +
> + /*
> + * Break huge page into small pages if the WP operation need to
> + * be performed is on a portion of the huge page.
> + */
> + if (is_written && IS_PM_SCAN_WP(p->flags) &&
> + n_pages < HPAGE_SIZE/PAGE_SIZE) {
> + spin_unlock(ptl);
> +
> + split_huge_pmd(vma, pmd, start);
> + goto process_smaller_pages;
> + }
> +
> + bitmap = PM_SCAN_FLAGS(is_written, (bool)vma->vm_file,
> + pmd_present(*pmd), is_swap_pmd(*pmd));
> +
> + if (IS_PM_SCAN_GET(p->flags)) {
> + is_interesting = pagemap_scan_is_interesting_page(bitmap, p);
> + if (is_interesting)
> + ret = pagemap_scan_output(bitmap, p, start, n_pages);
> + }
> +
> + if (IS_PM_SCAN_WP(p->flags) && is_written && is_interesting &&
> + ret >= 0) {
> + make_uffd_wp_pmd(vma, start, pmd);
> + flush_tlb_range(vma, start, end);
> + }
> +
> + spin_unlock(ptl);
> +
> + arch_leave_lazy_mmu_mode();
> + return ret;
> + }
> +
> +process_smaller_pages:
> +#endif
> +
> + orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
> + if (!pte) {
Do we need to unlock ptl here?
spin_unlock(ptl);
> + walk->action = ACTION_AGAIN;
> + return 0;
> + }
> +
> + for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) {
> + ptent = ptep_get(pte);
> + is_written = !is_pte_uffd_wp(ptent);
> +
> + bitmap = PM_SCAN_FLAGS(is_written, (bool)vma->vm_file,
> + pte_present(ptent), is_swap_pte(ptent));
The vma->vm_file check isn't correct in this case. You can look when
pte_to_pagemap_entry sets PM_FILE. This flag is used to detect what
pages have a file backing store and what pages are anonymous.
I was trying to integrate this new interace into CRIU and I found
one more thing that is required. We need to detect zero pages.
It should look something like this:
#define PM_SCAN_FLAGS(wt, file, present, swap, zero) \
((wt) | ((file) << 1) | ((present) << 2) | ((swap) << 3) | ((zero) << 4))
bitmap = PM_SCAN_FLAGS(is_written, page && !PageAnon(page),
pte_present(ptent), is_swap_pte(ptent),
pte_present(ptent) && is_zero_pfn(pte_pfn(ptent)));
Thanks,
Andrei
