Hi,
On 3/4/2025 11:18 AM, Emil Tsalapatis wrote:
> Hi,
>
> On Fri, Feb 28, 2025 at 7:56 PM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote:
>> Hi,
>>
>> On 2/28/2025 8:33 AM, Emil Tsalapatis wrote:
>>> Add a helper kfunc that sets the bitmap of a bpf_cpumask from BPF
>>> memory.
>>>
>>> Signed-off-by: Emil Tsalapatis (Meta) <emil@xxxxxxxxxxxxxxx>
>>> ---
>>> kernel/bpf/cpumask.c | 21 +++++++++++++++++++++
>>> 1 file changed, 21 insertions(+)
>>>
>>> diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
>>> index cfa1c18e3a48..a13839b3595f 100644
>>> --- a/kernel/bpf/cpumask.c
>>> +++ b/kernel/bpf/cpumask.c
>>> @@ -420,6 +420,26 @@ __bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
>>> return cpumask_weight(cpumask);
>>> }
>>>
>>> +/**
>>> + * bpf_cpumask_fill() - Populate the CPU mask from the contents of
>>> + * a BPF memory region.
>>> + *
>>> + * @cpumask: The cpumask being populated.
>>> + * @src: The BPF memory holding the bit pattern.
>>> + * @src__sz: Length of the BPF memory region in bytes.
>>> + *
>>> + */
>>> +__bpf_kfunc int bpf_cpumask_fill(struct cpumask *cpumask, void *src, size_t src__sz)
>>> +{
>>> + /* The memory region must be large enough to populate the entire CPU mask. */
>>> + if (src__sz < BITS_TO_BYTES(nr_cpu_ids))
>>> + return -EACCES;
>>> +
>>> + bitmap_copy(cpumask_bits(cpumask), src, nr_cpu_ids);
>> Should we use src__sz < bitmap_size(nr_cpu_ids) instead ? Because in
>> bitmap_copy(), it assumes the size of src should be bitmap_size(nr_cpu_ids).
> This is a great catch, thank you. Comparing with
> BITS_TO_BYTES(nr_cpu_ids) allows byte-aligned
> masks through, even though bitmap_copy assumes all masks are long-aligned.
Er, the long-aligned assumption raises another problem. Do we need to
make the src pointer be long-aligned because bitmap_copy() may use "*dst
= *src" to dereference the src pointer ? Or would it be better to use
memcpy() to copy the cpumask directly ?
>>> +
>>> + return 0;
>>> +}
>>> +
>>> __bpf_kfunc_end_defs();
>>>
>>> BTF_KFUNCS_START(cpumask_kfunc_btf_ids)
>>> @@ -448,6 +468,7 @@ BTF_ID_FLAGS(func, bpf_cpumask_copy, KF_RCU)
>>> BTF_ID_FLAGS(func, bpf_cpumask_any_distribute, KF_RCU)
>>> BTF_ID_FLAGS(func, bpf_cpumask_any_and_distribute, KF_RCU)
>>> BTF_ID_FLAGS(func, bpf_cpumask_weight, KF_RCU)
>>> +BTF_ID_FLAGS(func, bpf_cpumask_fill, KF_RCU)
>>> BTF_KFUNCS_END(cpumask_kfunc_btf_ids)
>>>
>>> static const struct btf_kfunc_id_set cpumask_kfunc_set = {
