Re: [PATCH bpf-next 0/4] selftests/bpf: Fix a few test failures with arm64 64KB page

[Yonghong Song <yonghong.song@linux.dev>]

On 6/6/25 9:49 AM, Ihor Solodrai wrote:
> On 6/6/25 9:43 AM, Yonghong Song wrote:
>>
>>
>> On 6/6/25 9:30 AM, Andrii Nakryiko wrote:
>>> On Thu, Jun 5, 2025 at 8:23 PM Yonghong Song 
>>> <yonghong.song@linux.dev> wrote:
>>>> My local arm64 host has 64KB page size and the VM to run test_progs
>>>> also has 64KB page size. There are a few self tests assuming 4KB page
>>>> and hence failed in my envorinment. Patch 1 tries to reduce long 
>>>> assert
>>> typo: environment
>>>
>>>> logs when tail failed. Patches 2-4 fixed three selftest failures.
>>> How come our BPF CI doesn't catch this on aarch64?.. Ihor, any 
>>> thoughts?
>>
>> In CI for aarch64, the page size is 4KB. For example, for this link:
>>
>> https://github.com/kernel-patches/bpf/actions/runs/15482212552/ 
>> job/43590176563?pr=9053
>>
>> Find the kconfig, and we have
>>
>>    CONFIG_ARM64_4K_PAGES=y
>>    # CONFIG_ARM64_16K_PAGES is not set
>>    # CONFIG_ARM64_64K_PAGES is not set
>>
>> and for 4K page, all these tests are fine, but not for 64K page.
>
> Ah right, I just realized the host pagesize doesn't matter, the kernel
> we are running tests against needs to be re-compiled with the right
> config.

Actually, the host pagesize matters too.

For example, for trace_printk.lskel.h which is used to build bpf binary at
an aarch64 host and that aarch64 host is 64KB page.
In trace_printk.lskel.h, we have
    ...
    skel->bss = skel_finalize_map_data(&skel->maps.bss.initial_value,
        65536, PROT_READ | PROT_WRITE, skel->maps.bss.map_fd);
    ...

Note that the number '65536' is used here to do mmap.

For an x86 host, the number will be 4096 (4KB) instead of 64KB.

For this bpf prog on aarch64, if the VM has page size 4KB,
something could go wrong.

So the best is to have the same page size for host and VM for selftests.


>
> If this is important to test on CI, it can be another matrix dimension
> with customized kconfig. Do we want to do that?
>
>
>>
>>
>>>
>>>> Yonghong Song (4):
>>>>    selftests/bpf: Reduce test_xdp_adjust_frags_tail_grow logs
>>>>    selftests/bpf: Fix bpf_mod_race test failure with arm64 64KB 
>>>> page size
>>>>    selftests/bpf: Fix ringbuf/ringbuf_write test failure with arm64 
>>>> 64KB
>>>>      page size
>>>>    selftests/bpf: Fix a user_ringbuf failure with arm64 64KB page size
>>>>
>>>>   .../selftests/bpf/prog_tests/bpf_mod_race.c    |  2 +-
>>>>   .../testing/selftests/bpf/prog_tests/ringbuf.c |  5 +++--
>>>>   .../selftests/bpf/prog_tests/user_ringbuf.c    |  6 ++++--
>>>>   .../selftests/bpf/prog_tests/xdp_adjust_tail.c | 18 
>>>> ++++++++++++------
>>>>   .../selftests/bpf/progs/test_ringbuf_write.c   |  5 +++--
>>>>   5 files changed, 23 insertions(+), 13 deletions(-)
>>>>
>>>> -- 
>>>> 2.47.1
>>>>
>>
>