Commit d937bc3449fa ("bpf: make uniform use of array->elem_size
everywhere in arraymap.c") changed array_map_gen_lookup to use
array->elem_size instead of round_up(map->value_size, 8) as the element
size when generating code to access a value in an array map.

array->elem_size, however, is not set by bpf_map_meta_alloc when
initializing an BPF_MAP_TYPE_ARRAY_OF_MAPS or BPF_MAP_TYPE_HASH_OF_MAPS.
This results in array_map_gen_lookup incorrectly outputting code that
always accesses index 0 in the array (as the index will be calculated
via a multiplication with the element size, which is incorrectly set to
0).

This patchset sets elem_size on the bpf_array object when allocating an
array or hash of maps to fix this and adds a selftest that accesses an
array map nested within a hash of maps at a nonzero index to prevent
regressions.

v1: https://lore.kernel.org/bpf/95b5da7c-ee52-3ecb-0a4e-f6a7a114f269@linux.dev/

Changelog:

v1 -> v2:

Address comments by Martin KaFai Lau:
- Directly use inner_array->elem_size instead of using round_up
- Move selftests to a new patch
- Use ASSERT_* macros instead of CHECK and remove duration
- Remove unnecessary usleep
- Shorten selftest name

Rhys Rustad-Elliott (2):
  bpf: Fix elem_size not being set for inner maps
  selftests/bpf: Add access_inner_map selftest

 kernel/bpf/map_in_map.c                       |  8 +++-
 .../bpf/prog_tests/inner_array_lookup.c       | 31 +++++++++++++
 .../bpf/progs/test_inner_array_lookup.c       | 45 +++++++++++++++++++
 3 files changed, 82 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/inner_array_lookup.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_inner_array_lookup.c

-- 
2.40.1