On Tue, Feb 6, 2024 at 12:14 AM Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
>
> Add three new kfuncs for bpf_iter_cpumask.
> - bpf_iter_cpumask_new
> KF_RCU is defined because the cpumask must be a RCU trusted pointer
> such as task->cpus_ptr.
> - bpf_iter_cpumask_next
> - bpf_iter_cpumask_destroy
>
> These new kfuncs facilitate the iteration of percpu data, such as
> runqueues, psi_cgroup_cpu, and more.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
> kernel/bpf/cpumask.c | 79 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 79 insertions(+)
>
> diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
> index dad0fb1c8e87..ed6078cfa40e 100644
> --- a/kernel/bpf/cpumask.c
> +++ b/kernel/bpf/cpumask.c
> @@ -422,6 +422,82 @@ __bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
> return cpumask_weight(cpumask);
> }
>
> +struct bpf_iter_cpumask {
> + __u64 __opaque[2];
> +} __aligned(8);
> +
> +struct bpf_iter_cpumask_kern {
> + struct cpumask *mask;
> + int cpu;
> +} __aligned(8);
> +
> +/**
> + * bpf_iter_cpumask_new() - Initialize a new CPU mask iterator for a given CPU mask
> + * @it: The new bpf_iter_cpumask to be created.
> + * @mask: The cpumask to be iterated over.
> + *
> + * This function initializes a new bpf_iter_cpumask structure for iterating over
> + * the specified CPU mask. It assigns the provided cpumask to the newly created
> + * bpf_iter_cpumask @it for subsequent iteration operations.
> + *
> + * On success, 0 is returned. On failure, ERR is returned.
> + */
> +__bpf_kfunc int bpf_iter_cpumask_new(struct bpf_iter_cpumask *it, const struct cpumask *mask)
> +{
> + struct bpf_iter_cpumask_kern *kit = (void *)it;
> +
> + BUILD_BUG_ON(sizeof(struct bpf_iter_cpumask_kern) > sizeof(struct bpf_iter_cpumask));
> + BUILD_BUG_ON(__alignof__(struct bpf_iter_cpumask_kern) !=
> + __alignof__(struct bpf_iter_cpumask));
> +
> + kit->mask = bpf_mem_alloc(&bpf_global_ma, cpumask_size());
> + if (!kit->mask)
> + return -ENOMEM;
> +
> + cpumask_copy(kit->mask, mask);
Since it's mem_alloc plus memcpy how about we make it more
generic ?
Instead of cpumask specific let's pass arbitrary
"void *unsafe_addr, u32 size"
allocate that much and probe_read_kernel into the buffer?
> +__bpf_kfunc int *bpf_iter_cpumask_next(struct bpf_iter_cpumask *it)
> +{
> + struct bpf_iter_cpumask_kern *kit = (void *)it;
> + const struct cpumask *mask = kit->mask;
> + int cpu;
> +
> + if (!mask)
> + return NULL;
> + cpu = cpumask_next(kit->cpu, mask);
Instead of cpumask_next() call find_next_bit()
> + if (cpu >= nr_cpu_ids)
> + return NULL;
instead of nr_cpu_ids we can check size in bits of copied bit array.
> BTF_ID_FLAGS(func, bpf_iter_cpumask_new, KF_ITER_NEW | KF_RCU)
KF_RCU is also not needed.
Such iterator will be callable from anywhere and on any address.
wdyt?
