On Thu, Jan 23, 2025 at 02:38:46PM +0000, Ryan Roberts wrote:
@@ -5470,7 +5471,18 @@ static void move_huge_pte(struct vm_area_struct *vma, unsigned long old_addr, spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); pte = huge_ptep_get_and_clear(mm, old_addr, src_pte);
- set_huge_pte_at(mm, new_addr, dst_pte, pte, sz);
- if (need_clear_uffd_wp && pte_marker_uffd_wp(pte))
huge_pte_clear(mm, new_addr, dst_pte, sz);This is checking if the source huge_pte is a uffd-wp marker and clearing the destination if so. The destination could have previously held arbitrary valid mappings, I guess?
I think it should be all cleared. I didn't check all mremap paths, but for MREMAP_FIXED at least there should be:
if (flags & MREMAP_FIXED) { /* * In mremap_to(). * VMA is moved to dst address, and munmap dst first. * do_munmap will check if dst is sealed. */ ret = do_munmap(mm, new_addr, new_len, uf_unmap_early); if (ret) goto out; }
It also doesn't sound right to leave anything in dest range, e.g. if there can be any leftover dest ptes in move_page_tables(), then it means HPAGE_P[MU]D won't work, as they install huge entries directly. For that I do see a hint in the comment too in that path:
move_normal_pud(): /* * The destination pud shouldn't be established, free_pgtables() * should have released it. */ if (WARN_ON_ONCE(!pud_none(*new_pud))) return false;
PMD path has similar implications.
Thanks,