Commit
0cf18e839f64 of large folio zap work broke uffd-wp. Now mm's uffd
unit test "wp-unpopulated" will trigger this WARN_ON_ONCE().
The WARN_ON_ONCE() asserts that an VMA cannot be registered with
userfaultfd-wp if it contains a !normal page, but it's actually possible.
One example is an anonymous vma, register with uffd-wp, read anything will
install a zero page. Then when zap on it, this should trigger.
What's more, removing that WARN_ON_ONCE may not be enough either, because
we should also not rely on "whether it's a normal page" to decide whether
pte marker is needed. For example, one can register wr-protect over some
DAX regions to track writes when UFFD_FEATURE_WP_ASYNC enabled, in which
case it can have page==NULL for a devmap but we may want to keep the
marker around.
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 0cf18e839f64 ("mm/memory: handle !page case in zap_present_pte() separately")
Signed-off-by: Peter Xu <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Muhammad Usama Anjum <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
arch_check_zapped_pte(vma, ptent);
tlb_remove_tlb_entry(tlb, pte, addr);
- VM_WARN_ON_ONCE(userfaultfd_wp(vma));
+ if (userfaultfd_pte_wp(vma, ptent))
+ zap_install_uffd_wp_if_needed(vma, addr, pte, 1,
+ details, ptent);
ksm_might_unmap_zero_page(mm, ptent);
return 1;
}