Re: [PATCH v2 3/6] mm: userfaultfd: support UFFDIO_POISON for hugetlbfs

On Thu, Jun 29, 2023 at 01:50:37PM -0700, Axel Rasmussen wrote:

The behavior here is the same as it is for anon/shmem. This is done separately because hugetlb pte marker handling is a bit different.

Signed-off-by: Axel Rasmussen axelrasmussen@google.com

mm/hugetlb.c | 33 +++++++++++++++++++++++++++++++-- mm/userfaultfd.c | 6 +----- 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 38711d49e4db..05abe88986b6 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6090,14 +6090,24 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, } entry = huge_ptep_get(ptep);

• /* PTE markers should be handled the same way as none pte */
• if (huge_pte_none_mostly(entry))

• if (huge_pte_none_mostly(entry)) {

• if (is_pte_marker(entry)) {
  

• 	unsigned long marker = pte_marker_get(pte_to_swp_entry(entry));
  

• 	if (marker & PTE_MARKER_UFFD_POISON) {
  

• 		ret = VM_FAULT_HWPOISON_LARGE;
  

• 		goto out_mutex;
  

• 	}
  

• }
  

  /*

•  * Other PTE markers should be handled the same way as none PTE.
  

•  *
  

  • hugetlb_no_page will drop vma lock and hugetlb fault
  • mutex internally, which make us return immediately.
  */ return hugetlb_no_page(mm, vma, mapping, idx, address, ptep, entry, flags);
• }

ret = 0; @@ -6253,6 +6263,25 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte, int writable; bool folio_in_pagecache = false;

• if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) {

• ptl = huge_pte_lock(h, dst_mm, dst_pte);
  

• /* Don't overwrite any existing PTEs (even markers) */
  

• if (!huge_pte_none(huge_ptep_get(dst_pte))) {
  

• 	spin_unlock(ptl);
  

• 	return -EEXIST;
  

• }
  

• _dst_pte = make_pte_marker(PTE_MARKER_UFFD_POISON);
  

• set_huge_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
  

• /* No need to invalidate - it was non-present before */
  

• update_mmu_cache(dst_vma, dst_addr, dst_pte);
  

• spin_unlock(ptl);
  

• return 0;
  

• }
• if (is_continue) { ret = -EFAULT; folio = filemap_lock_folio(mapping, idx);

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 87b62ca1e09e..4436cae1c7a8 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -381,12 +381,8 @@ static __always_inline ssize_t mfill_atomic_hugetlb( * supported by hugetlb. A PMD_SIZE huge pages may exist as used * by THP. Since we can not reliably insert a zero page, this * feature is not supported.

• *
  

• * PTE marker handling for hugetlb is a bit special, so for now
  

• * UFFDIO_POISON is not supported.
  

  */
• if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE) ||

•    uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) {
  

• if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) { mmap_read_unlock(dst_mm); return -EINVAL;

If we have the last patch declaring the feature bits and so on, IIUC we don'tt need this change back and forth. Other than that looks good.

Thanks,

}

2.41.0.255.g8b1d071c50-goog