On 6/9/25 3:55 PM, Stanislav Fomichev wrote:
On 06/08, Yonghong Song wrote:When running BPF selftests on arm64 with a 64K page size, I encountered the following two test failures: sockmap_basic/sockmap skb_verdict change tail:FAIL tc_change_tail:FAIL With further debugging, I identified the root cause in the following kernel code within __bpf_skb_change_tail(): u32 max_len = BPF_SKB_MAX_LEN; u32 min_len = __bpf_skb_min_len(skb); int ret; if (unlikely(flags || new_len > max_len || new_len < min_len)) return -EINVAL; With a 4K page size, new_len = 65535 and max_len = 16064, the function returns -EINVAL. However, With a 64K page size, max_len increases to 261824, allowing execution to proceed further in the function. This is because BPF_SKB_MAX_LEN scales with the page size and larger page sizes result in higher max_len values. Updating the new_len parameter in both tests from 65535 to 262143 (0x3ffff) resolves the failures. Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx> --- tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c | 2 +- tools/testing/selftests/bpf/progs/test_tc_change_tail.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c b/tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c index 2796dd8545eb..4f7f08364c75 100644 --- a/tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c +++ b/tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c @@ -31,7 +31,7 @@ int prog_skb_verdict(struct __sk_buff *skb) change_tail_ret = bpf_skb_change_tail(skb, skb->len + 1, 0); return SK_PASS; } else if (data[0] == 'E') { /* Error */ - change_tail_ret = bpf_skb_change_tail(skb, 65535, 0); + change_tail_ret = bpf_skb_change_tail(skb, 262143, 0); return SK_PASS; } return SK_PASS; diff --git a/tools/testing/selftests/bpf/progs/test_tc_change_tail.c b/tools/testing/selftests/bpf/progs/test_tc_change_tail.c index 28edafe803f0..b1057fda58a0 100644 --- a/tools/testing/selftests/bpf/progs/test_tc_change_tail.c +++ b/tools/testing/selftests/bpf/progs/test_tc_change_tail.c @@ -94,7 +94,7 @@ int change_tail(struct __sk_buff *skb) bpf_skb_change_tail(skb, len, 0); return TCX_PASS; } else if (payload[0] == 'E') { /* Error */ - change_tail_ret = bpf_skb_change_tail(skb, 65535, 0); + change_tail_ret = bpf_skb_change_tail(skb, 262143, 0); return TCX_PASS; } else if (payload[0] == 'Z') { /* Zero */ change_tail_ret = bpf_skb_change_tail(skb, 0, 0);nit: this seems to be exercising BPF_SKB_MAX_LEN case. To make it easier to spot in the future, can we do the following in both tests? #define PAGE_SIZE 65536 /* make it work on 64K page arches */ #define BPF_SKB_MAX_LEN (PAGE_SIZE << 2) ... = bpf_skb_change_tail(skb, BPF_SKB_MAX_LEN, 0);
Thanks for suggestions, Will do.
