Critical fixes for mmap_region(), backported to 5.10.y.

Some notes on differences from upstream:

* We do NOT take commit 0fb4a7ad270b ("mm: refactor
  map_deny_write_exec()"), as this refactors code only introduced in 6.2.

* We make reference in "mm: refactor arch_calc_vm_flag_bits() and arm64 MTE
  handling" to parisc, but the referenced functionality does not exist in
  this kernel.

* In this kernel is_shared_maywrite() does not exist and the code uses
  VM_SHARED to determine whether mapping_map_writable() /
  mapping_unmap_writable() should be invoked. This backport therefore
  follows suit.

* The vma_dummy_vm_ops static global doesn't exist in this kernel, so we
  use a local static variable in mmap_file() and vma_close().

* Each version of these series is confronted by a slightly different
  mmap_region(), so we must adapt the change for each stable version. The
  approach remains the same throughout, however, and we correctly avoid
  closing the VMA part way through any __mmap_region() operation.

* In 5.10 we must handle VM_DENYWRITE. Since this is done at the top of the
  file-backed VMA handling logic, and importantly before mmap_file() invocation,
  this does not imply any additional difficult error handling on partial
  completion of mapping so has no significant impact.

Lorenzo Stoakes (4):
  mm: avoid unsafe VMA hook invocation when error arises on mmap hook
  mm: unconditionally close VMAs on error
  mm: refactor arch_calc_vm_flag_bits() and arm64 MTE handling
  mm: resolve faulty mmap_region() error path behaviour

 arch/arm64/include/asm/mman.h | 10 +++--
 include/linux/mman.h          |  7 +--
 mm/internal.h                 | 19 ++++++++
 mm/mmap.c                     | 82 +++++++++++++++++++++--------------
 mm/nommu.c                    |  9 ++--
 mm/shmem.c                    |  3 --
 mm/util.c                     | 33 ++++++++++++++
 7 files changed, 117 insertions(+), 46 deletions(-)

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2.47.0