Re: [PATCH v13 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

Muhammad,

On Mon, Apr 17, 2023 at 05:56:27PM +0500, Muhammad Usama Anjum wrote:

+static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,

• 		  unsigned long end, struct mm_walk *walk)
  

+{

• struct pagemap_scan_private *p = walk->private;
• struct vm_area_struct *vma = walk->vma;
• unsigned long addr = end;
• pte_t *pte, *orig_pte;
• spinlock_t *ptl;
• bool is_written;
• int ret = 0;

+#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 && PM_SCAN_DO_UFFD_WP(p) &&
  

•     n_pages < HPAGE_SIZE/PAGE_SIZE) {
  

• 	spin_unlock(ptl);
  

• 	split_huge_pmd(vma, pmd, start);
  

• 	goto process_smaller_pages;
  

• }
  

• ret = pagemap_scan_output(is_written, vma->vm_file,
  

• 			  pmd_present(*pmd), is_swap_pmd(*pmd),
  

• 			  p, start, n_pages);
  

• if (ret >= 0 && is_written && PM_SCAN_DO_UFFD_WP(p))
  

• 	make_uffd_wp_pmd(vma, addr, pmd);
  

• spin_unlock(ptl);
  

• return ret;
  

• }

+process_smaller_pages:

• if (pmd_trans_unstable(pmd))

• return 0;
  

+#endif

• pte = pte_offset_map_lock(vma->vm_mm, pmd, start, &ptl);
• for (addr = start; addr < end && !ret; pte++, addr += PAGE_SIZE) {

• is_written = !is_pte_uffd_wp(*pte);
  

• ret = pagemap_scan_output(is_written, vma->vm_file,
  

• 			  pte_present(*pte), is_swap_pte(*pte),
  

• 			  p, addr, 1);
  

• if (ret >= 0 && is_written && PM_SCAN_DO_UFFD_WP(p))
  

• 	make_uffd_wp_pte(vma, addr, pte);
  

• }
• pte_unmap_unlock(orig_pte, ptl);

IIUC tlb flushes, mmu notifications are still missing here, am I right?

Thanks,

• cond_resched();
• return ret;

+}