On 4/24/24 10:36 PM, Yafang Shao wrote:
On Thu, Apr 25, 2024 at 8:34 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
On Thu, Apr 11, 2024 at 6:51 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
On Thu, Apr 11, 2024 at 9:11 PM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
Three new kfuncs, namely bpf_iter_bits_{new,next,destroy}, have been
added for the new bpf_iter_bits functionality. These kfuncs enable the
iteration of the bits from a given address and a given number of bits.
- bpf_iter_bits_new
Initialize a new bits iterator for a given memory area. Due to the
limitation of bpf memalloc, the max number of bits to be iterated
over is (4096 * 8).
- bpf_iter_bits_next
Get the next bit in a bpf_iter_bits
- bpf_iter_bits_destroy
Destroy a bpf_iter_bits
The bits iterator can be used in any context and on any address.
Changes:
- v5->v6:
- Add positive tests (Andrii)
- v4->v5:
- Simplify test cases (Andrii)
- v3->v4:
- Fix endianness error on s390x (Andrii)
- zero-initialize kit->bits_copy and zero out nr_bits (Andrii)
- v2->v3:
- Optimization for u64/u32 mask (Andrii)
- v1->v2:
- Simplify the CPU number verification code to avoid the failure on s390x
(Eduard)
- bpf: Add bpf_iter_cpumask
https://lwn.net/Articles/961104/
- bpf: Add new bpf helper bpf_for_each_cpu
https://lwn.net/Articles/939939/
Yafang Shao (2):
bpf: Add bits iterator
selftests/bpf: Add selftest for bits iter
kernel/bpf/helpers.c | 120 +++++++++++++++++
.../selftests/bpf/prog_tests/verifier.c | 2 +
.../selftests/bpf/progs/verifier_bits_iter.c | 127 ++++++++++++++++++
3 files changed, 249 insertions(+)
create mode 100644 tools/testing/selftests/bpf/progs/verifier_bits_iter.c
--
2.39.1
It appears that the test case failed on s390x when the data is
a u32 value because we need to set the higher 32 bits.
will analyze it.
Hey Yafang, did you get a chance to debug and fix the issue?
Hi Andrii,
Apologies for the delay; I recently returned from an extended holiday.
The issue stems from the limitations of bpf_probe_read_kernel() on
s390 architecture. The attachment provides a straightforward example
to illustrate this issue. The observed results are as follows:
Error: #463/1 verifier_probe_read/probe read 4 bytes
8897 run_subtest:PASS:obj_open_mem 0 nsec
8898 run_subtest:PASS:unexpected_load_failure 0 nsec
8899 do_prog_test_run:PASS:bpf_prog_test_run 0 nsec
8900 run_subtest:FAIL:659 Unexpected retval: 2817064 != 512
Error: #463/2 verifier_probe_read/probe read 8 bytes
8903 run_subtest:PASS:obj_open_mem 0 nsec
8904 run_subtest:PASS:unexpected_load_failure 0 nsec
8905 do_prog_test_run:PASS:bpf_prog_test_run 0 nsec
8906 run_subtest:FAIL:659 Unexpected retval: 0 != 512
More details can be found at: https://github.com/kernel-patches/bpf/pull/6872
Should we consider this behavior of bpf_probe_read_kernel() as
expected, or is it something that requires fixing?
Maybe to guard the result with macros like __s390x__ to differentiate
s390 vs. arm64/x86_64? There are some examples in prog_tests/* having
such guards. probe_user.c:#if defined(__s390x__)
test_bpf_syscall_macro.c:#if defined(__aarch64__) || defined(__s390__)
xdp_adjust_tail.c:#if defined(__s390x__) xdp_do_redirect.c:#if
defined(__s390x__)
