bpf: add kfunc for populating cpumask bits

Add a helper kfunc that sets the bitmap of a bpf_cpumask from BPF memory.

Signed-off-by: Emil Tsalapatis (Meta) <emil@etsalapatis.com>
Acked-by: Hou Tao <houtao1@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20250309230427.26603-2-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
index cfa1c18e3a48..77900cbbbd75 100644
--- a/kernel/bpf/cpumask.c
+++ b/kernel/bpf/cpumask.c
@@ -420,6 +420,38 @@ __bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
 	return cpumask_weight(cpumask);
 }
 
+/**
+ * bpf_cpumask_populate() - 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.
+ *
+ * Return:
+ * * 0 if the struct cpumask * instance was populated successfully.
+ * * -EACCES if the memory region is too small to populate the cpumask.
+ * * -EINVAL if the memory region is not aligned to the size of a long
+ *   and the architecture does not support efficient unaligned accesses.
+ */
+__bpf_kfunc int bpf_cpumask_populate(struct cpumask *cpumask, void *src, size_t src__sz)
+{
+	unsigned long source = (unsigned long)src;
+
+	/* The memory region must be large enough to populate the entire CPU mask. */
+	if (src__sz < bitmap_size(nr_cpu_ids))
+		return -EACCES;
+
+	/* If avoiding unaligned accesses, the input region must be aligned to the nearest long. */
+	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&
+		!IS_ALIGNED(source, sizeof(long)))
+		return -EINVAL;
+
+	bitmap_copy(cpumask_bits(cpumask), src, nr_cpu_ids);
+
+	return 0;
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_KFUNCS_START(cpumask_kfunc_btf_ids)
@@ -448,6 +480,7 @@ 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_populate, KF_RCU)
 BTF_KFUNCS_END(cpumask_kfunc_btf_ids)
 
 static const struct btf_kfunc_id_set cpumask_kfunc_set = {