For platforms on powerpc architecture with a default page size greater than 4096, there was an inconsistency in fragment size calculation. This caused the BPF selftest xdp_adjust_tail/xdp_adjust_frags_tail_grow to fail on powerpc.
The issue occurred because the fragment buffer size in bpf_prog_test_run_xdp() was set to 4096, while the actual data size in the fragment within the shared skb was checked against PAGE_SIZE (65536 on powerpc) in min_t, causing it to exceed 4096 and be set accordingly. This discrepancy led to an overflow when bpf_xdp_frags_increase_tail() checked for tailroom, as skb_frag_size(frag) could be greater than rxq->frag_size (when PAGE_SIZE > 4096).
This change fixes:
1. test_run by getting the correct arch dependent PAGE_SIZE. 2. selftest by caculating tailroom and getting correct PAGE_SIZE.
Changes: v1 -> v2: * Address comments from Alexander * Use dynamic page size, cacheline size and size of struct skb_shared_info to calculate parameters. * Fixed both test_run and selftest.
v1: https://lore.kernel.org/all/20250122183720.1411176-1-skb99@linux.ibm.com/
Saket Kumar Bhaskar (2): bpf, test_run: Replace hardcoded page size with dynamic PAGE_SIZE in test_run selftests/bpf: Refactor xdp_adjust_tail selftest with dynamic sizing
.../bpf/prog_tests/xdp_adjust_tail.c | 160 +++++++++++++----- .../bpf/progs/test_xdp_adjust_tail_grow.c | 41 +++-- 2 files changed, 149 insertions(+), 52 deletions(-)