On 7/25/25 4:29 PM, Martin KaFai Lau wrote:
On 7/24/25 9:34 PM, Yonghong Song wrote:
For arm64 64K page size, the xdp data size was set to be more than 64K
in one of previous patches. This will cause failure for
bpf_dynptr_memset().
Since the failure of bpf_dynptr_memset() is expected with 64K page size,
return success.
Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
tools/testing/selftests/bpf/progs/dynptr_success.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/bpf/progs/dynptr_success.c
b/tools/testing/selftests/bpf/progs/dynptr_success.c
index 3094a1e4ee91..8315273cb900 100644
--- a/tools/testing/selftests/bpf/progs/dynptr_success.c
+++ b/tools/testing/selftests/bpf/progs/dynptr_success.c
@@ -9,6 +9,8 @@
#include "bpf_misc.h"
#include "errno.h"
+#define PAGE_SIZE_64K 65536
+
char _license[] SEC("license") = "GPL";
int pid, err, val;
@@ -821,8 +823,17 @@ int test_dynptr_memset_xdp_chunks(struct xdp_md
*xdp)
data_sz = bpf_dynptr_size(&ptr_xdp);
err = bpf_dynptr_memset(&ptr_xdp, 0, data_sz,
DYNPTR_MEMSET_VAL);
- if (err)
+ if (err) {
+ /* bpf_dynptr_memset() eventually called bpf_xdp_pointer()
I don't think I understand why the test fixed in patch 1 (e.g.
test_probe_read_user_dynptr) can pass the bpf_xdp_pointer test on
0xffff. I thought the bpf_probe_read_user_str_dynptr will eventually
call the __bpf_xdp_store_bytes which also does a bpf_xdp_pointer?
For example, for test_probe_read_user_dynptr, for function test_dynptr_probe_xdp(),
for this one:
off = xdp_near_frag_end_offset();
the off = 64928. Note that xdp_near_frag_end_offset() return value depends page size.
__u32 xdp_near_frag_end_offset(void)
{
const __u32 headroom = 256;
const __u32 max_frag_size = __PAGE_SIZE - headroom - sizeof(struct skb_shared_info);
/* 32 bytes before the approximate end of the fragment */
return max_frag_size - 32;
}
The 'len' depends on 'test_len[i]' and test_len is
__u32 test_len[7] = {0/* placeholder */, 0, 1, 2, 255, 256, 257};
In bpf_xdp_pointer, we have the following test
if (unlikely(offset > 0xffff || len > 0xffff))
return ERR_PTR(-EFAULT);
In this particular case, offset = 64928, len = {0, 1, 2, 255, 256, 257}, so
it won't return -EFAULT.
For this patch 3, test_dynptr_memset_xdp_chunks, eventually we reached here:
for (write_off = 0; write_off < size; write_off += chunk_sz) {
chunk_sz = min_t(u32, sizeof(buf), size - write_off);
err = __bpf_dynptr_write(ptr, offset + write_off, buf, chunk_sz, 0);
if (err)
return err;
}
So the 'size' is 90000, chunk_sz is 256.
So 'offset + write_off' will be 0, 256, 512, ..., 65536
Once it reached 65536, 'offset > 0xffff' will become true since 0xffff = 65535.
and the -EFAULT will be returned.
+ * where if data_sz is greater than 0xffff, -EFAULT will be
+ * returned. For 64K page size, data_sz is greater than
+ * 64K, so error is expected and let us zero out error and
+ * return success.
+ */
+ if (data_sz >= PAGE_SIZE_64K)
+ err = 0;
goto out;
+ }
bpf_for(i, 0, max_chunks) {
offset = i * sizeof(buf);
