[v3,1/2] bpf: add kfunc for populating cpumask bits

Commit Message

Emil Tsalapatis March 5, 2025, 4:13 p.m. UTC

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

Signed-off-by: Emil Tsalapatis (Meta) <[e-mail]>
---
 kernel/bpf/cpumask.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

Comments

Alexei Starovoitov March 5, 2025, 5:50 p.m. UTC | #1

On Wed, Mar 5, 2025 at 8:13 AM Emil Tsalapatis <[e-mail]> wrote:
>
> Add a helper kfunc that sets the bitmap of a bpf_cpumask from BPF memory.
>
> Signed-off-by: Emil Tsalapatis (Meta) <[e-mail]>
> ---
>  kernel/bpf/cpumask.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
>
> diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
> index cfa1c18e3a48..2a0770544fc3 100644
> --- a/kernel/bpf/cpumask.c
> +++ b/kernel/bpf/cpumask.c
> @@ -420,6 +420,33 @@ __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.
> + *
> + */

Since you're adding kdoc, make it complete.
Otherwise there is a warn during the build:

> kernel/bpf/cpumask.c:433: warning: No description found for return value of 'bpf_cpumask_fill'

and while at it, could you fix it for other kfuncs?

kernel/bpf/cpumask.c:50: warning: No description found for return
value of 'bpf_cpumask_create'
kernel/bpf/cpumask.c:76: warning: No description found for return
value of 'bpf_cpumask_acquire'

Thanks!

Tejun Heo March 5, 2025, 6:27 p.m. UTC | #2

Hello,

On Wed, Mar 05, 2025 at 11:13:26AM -0500, Emil Tsalapatis wrote:
...
> +/**
> + * bpf_cpumask_fill() - Populate the CPU mask from the contents of
> + * a BPF memory region.

bitmap_fill() fills the bitmap with all 1's, so this name can be pretty
confusing. Maybe bpf_cpumask_populate_from() or something like that?

Thanks.

Patch

diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
index cfa1c18e3a48..2a0770544fc3 100644
--- a/kernel/bpf/cpumask.c
+++ b/kernel/bpf/cpumask.c
@@ -420,6 +420,33 @@  __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)
+{
+	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 +475,7 @@  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 = {