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    SubjectRe: [BUG] hugetlb MAP_PRIVATE mapping vs /dev/zero
    Oleg Nesterov <oleg@tv-sign.ru> wrote:
    >
    > Hugetlbfs mmap with MAP_PRIVATE becomes MAP_SHARED
    > silently, but vma->vm_flags have no VM_SHARED bit.
    > I think it make sense to forbid MAP_PRIVATE in
    > hugetlbfs_file_mmap() because it may confuse user
    > space applications. But the real bug is that reading
    > from /dev/zero into hugetlb will do:
    >
    > read_zero()
    > read_zero_pagealigned()
    > if (vma->vm_flags & VM_SHARED)
    > break; // OK if MAP_PRIVATE
    > zap_page_range();
    > zeromap_page_range();
    >
    > We can fix hugetlbfs_file_mmap() or read_zero_pagealigned()
    > or both.

    This could break existing applications, yes?

    If so, would an appropriate fixup be to coerce private mappings
    of hugetlb files into shared ones in-kernel?
    -
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