On 22/07/2025 18:03, Paolo Abeni wrote:
> On 7/21/25 8:34 PM, Gal Pressman wrote:
>> On 21/07/2025 18:40, Jakub Kicinski wrote:
>>> On Mon, 21 Jul 2025 14:43:15 +0300 Nimrod Oren wrote:
>>>>> +static struct udphdr *filter_udphdr(struct xdp_md *ctx, __u16 port)
>>>>> +{
>>>>> + void *data_end = (void *)(long)ctx->data_end;
>>>>> + void *data = (void *)(long)ctx->data;
>>>>> + struct udphdr *udph = NULL;
>>>>> + struct ethhdr *eth = data;
>>>>> +
>>>>> + if (data + sizeof(*eth) > data_end)
>>>>> + return NULL;
>>>>> +
>>>>
>>>> This check assumes that the packet headers reside in the linear part of
>>>> the xdp_buff. However, this assumption does not hold across all drivers.
>>>> For example, in mlx5, the linear part is empty when using multi-buffer
>>>> mode with striding rq configuration. This causes all multi-buffer test
>>>> cases to fail over mlx5.
>>>>
>>>> To ensure correctness across all drivers, all direct accesses to packet
>>>> data should use these safer helper functions instead:
>>>> bpf_xdp_load_bytes() and bpf_xdp_store_bytes().
>>>>
>>>> Related discussion and context can be found here:
>>>> https://github.com/xdp-project/xdp-tools/pull/409
>>>
>>> That's a reasonable way to modify the test. But I'm not sure it's
>>> something that should be blocking merging the patches.
>>> Or for that matter whether it's Mohsin's responsibility to make the
>>> test cater to quirks of mlx5,
>>
>> Definitely not a quirk, you cannot assume the headers are in the linear
>> part, especially if you're going to put this program as reference in the
>> kernel tree.
>>
>> This issue has nothing to do with mlx5, but a buggy XDP program.
>
> Note that with the self-tests we have a slightly different premise WRT
> the actual kernel code. We prefer on-boarding tests cases that work for
> some/most of the possible setup vs perfect ones, and eventually improve
> incrementally as needed: the goal is to increase the code coverage _and_
> encourage people to contribute new tests upstream.
The changes required to fix the test are trivial, and Nimrod provided a
reference for the conversion.
