[PATCH bpf-next 2/2] selftests/bpf: Fix two net related test failures with 64K page size

[Yonghong Song <yonghong.song@xxxxxxxxx>]

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);
-- 
2.47.1