Re: [PATCH bpf-next 3/3] selftests/bpf: Add tests for arena fault reporting

[<puranjay@kernel.org>]

Yonghong Song <yonghong.song@linux.dev> writes:

> On 8/6/25 1:58 AM, Puranjay Mohan wrote:
>> Add selftests for testing the reporting of arena page faults through BPF
>> streams. Two new bpf programs are added that read and write to an
>> unmapped arena address and the fault reporting is verified in the
>> userspace through streams.
>>
>> Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
>> ---
>>   .../testing/selftests/bpf/prog_tests/stream.c | 24 ++++++++++++
>>   tools/testing/selftests/bpf/progs/stream.c    | 37 +++++++++++++++++++
>>   2 files changed, 61 insertions(+)
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/stream.c b/tools/testing/selftests/bpf/prog_tests/stream.c
>> index d9f0185dca61b..4bdde56de35b1 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/stream.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/stream.c
>> @@ -41,6 +41,22 @@ struct {
>>   		"([a-zA-Z_][a-zA-Z0-9_]*\\+0x[0-9a-fA-F]+/0x[0-9a-fA-F]+\n"
>>   		"|[ \t]+[^\n]+\n)*",
>>   	},
>> +	{
>> +		offsetof(struct stream, progs.stream_arena_read_fault),
>> +		"ERROR: Arena READ access at unmapped address 0x.*\n"
>> +		"CPU: [0-9]+ UID: 0 PID: [0-9]+ Comm: .*\n"
>> +		"Call trace:\n"
>> +		"([a-zA-Z_][a-zA-Z0-9_]*\\+0x[0-9a-fA-F]+/0x[0-9a-fA-F]+\n"
>> +		"|[ \t]+[^\n]+\n)*",
>> +	},
>> +	{
>> +		offsetof(struct stream, progs.stream_arena_write_fault),
>> +		"ERROR: Arena WRITE access at unmapped address 0x.*\n"
>> +		"CPU: [0-9]+ UID: 0 PID: [0-9]+ Comm: .*\n"
>> +		"Call trace:\n"
>> +		"([a-zA-Z_][a-zA-Z0-9_]*\\+0x[0-9a-fA-F]+/0x[0-9a-fA-F]+\n"
>> +		"|[ \t]+[^\n]+\n)*",
>> +	},
>>   };
>>   
>>   static int match_regex(const char *pattern, const char *string)
>> @@ -85,6 +101,14 @@ void test_stream_errors(void)
>>   			continue;
>>   		}
>>   #endif
>> +#if !defined(__x86_64__) && !defined(__aarch64__)
>> +		ASSERT_TRUE(1, "Arena fault reporting unsupported, skip.");
>> +		if (i == 2 || i == 3) {
>> +			ret = bpf_prog_stream_read(prog_fd, 2, buf, sizeof(buf), &ropts);
>> +			ASSERT_EQ(ret, 0, "stream read");
>> +			continue;
>> +		}
>> +#endif
>>   
>>   		ret = bpf_prog_stream_read(prog_fd, BPF_STREAM_STDERR, buf, sizeof(buf), &ropts);
>>   		ASSERT_GT(ret, 0, "stream read");
>> diff --git a/tools/testing/selftests/bpf/progs/stream.c b/tools/testing/selftests/bpf/progs/stream.c
>> index 35790897dc879..58ebff60cd96a 100644
>> --- a/tools/testing/selftests/bpf/progs/stream.c
>> +++ b/tools/testing/selftests/bpf/progs/stream.c
>> @@ -1,10 +1,15 @@
>>   // SPDX-License-Identifier: GPL-2.0
>>   /* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
>> +#define BPF_NO_KFUNC_PROTOTYPES
>
> Do we have to defineBPF_NO_KFUNC_PROTOTYPES in the above? Without the above, we do not need 
> below extern bpf_res_spin_lock and bpf_res_spin_unlock.
>

If we don't define BPF_NO_KFUNC_PROTOTYPES then there are build failures
for bpf_arena_alloc/free_pages() because the prototypes in vmlinux.h
lack __arena attribute.

>> +
>> +	page = bpf_arena_alloc_pages(&arena, NULL, 1, NUMA_NO_NODE, 0);
>> +	bpf_arena_free_pages(&arena, page, 1);
>> +

Thanks,
Puranjay