On 6/11/25 12:21 PM, Alexei Starovoitov wrote:
On Wed, Jun 11, 2025 at 10:15 AM Yonghong Song <yonghong.song@xxxxxxxxx> 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 256K (0x40000) resolves the failures. Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx> --- tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c | 5 ++++- tools/testing/selftests/bpf/progs/test_tc_change_tail.c | 5 ++++- 2 files changed, 8 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..e4554ef05441 100644 --- a/tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c +++ b/tools/testing/selftests/bpf/progs/test_sockmap_change_tail.c @@ -3,6 +3,9 @@ #include <linux/bpf.h> #include <bpf/bpf_helpers.h> +#define PAGE_SIZE 65536 /* make it work on 64K page arches */ +#define BPF_SKB_MAX_LEN (PAGE_SIZE << 2) + struct { __uint(type, BPF_MAP_TYPE_SOCKMAP); __uint(max_entries, 1); @@ -31,7 +34,7 @@ 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, BPF_SKB_MAX_LEN, 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..47670bbd1766 100644 --- a/tools/testing/selftests/bpf/progs/test_tc_change_tail.c +++ b/tools/testing/selftests/bpf/progs/test_tc_change_tail.c @@ -7,6 +7,9 @@ #include <linux/udp.h> #include <linux/pkt_cls.h> +#define PAGE_SIZE 65536 /* make it work on 64K page arches */ +#define BPF_SKB_MAX_LEN (PAGE_SIZE << 2)If you want it to match the kernel then let's use actual page size? See bpf_arena_common.h and #ifndef PAGE_SIZE #define PAGE_SIZE __PAGE_SIZE
LGTM. This will allow to use actual page size...
