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    Subject[PATCH v2 16/24] hugetlb/userfaultfd: Hook page faults for uffd write protection
    Date
    Hook up hugetlbfs_fault() with the capability to handle userfaultfd-wp faults.

    We do this slightly earlier than hugetlb_cow() so that we can avoid taking some
    extra locks that we definitely don't need.

    Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
    Signed-off-by: Peter Xu <peterx@redhat.com>
    ---
    mm/hugetlb.c | 19 +++++++++++++++++++
    1 file changed, 19 insertions(+)

    diff --git a/mm/hugetlb.c b/mm/hugetlb.c
    index 629aa4c2259c8..8e234ee9a15e2 100644
    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -4802,6 +4802,25 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
    if (unlikely(!pte_same(entry, huge_ptep_get(ptep))))
    goto out_ptl;

    + /* Handle userfault-wp first, before trying to lock more pages */
    + if (userfaultfd_pte_wp(vma, huge_ptep_get(ptep)) &&
    + (flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
    + struct vm_fault vmf = {
    + .vma = vma,
    + .address = haddr,
    + .flags = flags,
    + };
    +
    + spin_unlock(ptl);
    + if (pagecache_page) {
    + unlock_page(pagecache_page);
    + put_page(pagecache_page);
    + }
    + mutex_unlock(&hugetlb_fault_mutex_table[hash]);
    + i_mmap_unlock_read(mapping);
    + return handle_userfault(&vmf, VM_UFFD_WP);
    + }
    +
    /*
    * hugetlb_cow() requires page locks of pte_page(entry) and
    * pagecache_page, so here we need take the former one
    --
    2.26.2
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