Merge branch 'add-new-bpf_cpumask_weight-kfunc'

David Vernet says:

====================
Add new bpf_cpumask_weight() kfunc

It can be useful to query how many bits are set in a cpumask. For
example, if you want to perform special logic for the last remaining
core that's set in a mask. This logic is already exposed through the
main kernel's cpumask header as cpumask_weight(), so it would be useful
to add a new bpf_cpumask_weight() kfunc which wraps it and does the
same.

This patch series was built and tested on top of commit 2146f7fe6e
("Merge branch 'allocate-bpf-trampoline-on-bpf_prog_pack'").
====================

Link: https://lore.kernel.org/r/20231207210843.168466-1-void@manifault.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Documentation/bpf/cpumasks.rst

@@ -352,7 +352,7 @@ can be used to query the contents of cpumasks.
 
 .. kernel-doc:: kernel/bpf/cpumask.c
    :identifiers: bpf_cpumask_first bpf_cpumask_first_zero bpf_cpumask_first_and
-                 bpf_cpumask_test_cpu
+                 bpf_cpumask_test_cpu bpf_cpumask_weight
 
 .. kernel-doc:: kernel/bpf/cpumask.c
    :identifiers: bpf_cpumask_equal bpf_cpumask_intersects bpf_cpumask_subset

kernel/bpf/cpumask.c

@@ -405,6 +405,17 @@ __bpf_kfunc u32 bpf_cpumask_any_and_distribute(const struct cpumask *src1,
 	return cpumask_any_and_distribute(src1, src2);
 }
 
+/**
+ * bpf_cpumask_weight() - Return the number of bits in @cpumask.
+ * @cpumask: The cpumask being queried.
+ *
+ * Count the number of set bits in the given cpumask.
+ */
+__bpf_kfunc u32 bpf_cpumask_weight(const struct cpumask *cpumask)
+{
+	return cpumask_weight(cpumask);
+}
+
 __bpf_kfunc_end_defs();
 
 BTF_SET8_START(cpumask_kfunc_btf_ids)
@@ -432,6 +443,7 @@ BTF_ID_FLAGS(func, bpf_cpumask_full, KF_RCU)
 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_SET8_END(cpumask_kfunc_btf_ids)
 
 static const struct btf_kfunc_id_set cpumask_kfunc_set = {

tools/testing/selftests/bpf/prog_tests/cpumask.c

@@ -18,6 +18,7 @@ static const char * const cpumask_success_testcases[] = {
 	"test_insert_leave",
 	"test_insert_remove_release",
 	"test_global_mask_rcu",
+	"test_cpumask_weight",
 };
 
 static void verify_success(const char *prog_name)

tools/testing/selftests/bpf/progs/cpumask_common.h

@@ -54,6 +54,7 @@ bool bpf_cpumask_full(const struct cpumask *cpumask) __ksym;
 void bpf_cpumask_copy(struct bpf_cpumask *dst, const struct cpumask *src) __ksym;
 u32 bpf_cpumask_any_distribute(const struct cpumask *src) __ksym;
 u32 bpf_cpumask_any_and_distribute(const struct cpumask *src1, const struct cpumask *src2) __ksym;
+u32 bpf_cpumask_weight(const struct cpumask *cpumask) __ksym;
 
 void bpf_rcu_read_lock(void) __ksym;
 void bpf_rcu_read_unlock(void) __ksym;

tools/testing/selftests/bpf/progs/cpumask_success.c

@@ -460,6 +460,49 @@ int BPF_PROG(test_global_mask_rcu, struct task_struct *task, u64 clone_flags)
 	return 0;
 }
 
+SEC("tp_btf/task_newtask")
+int BPF_PROG(test_cpumask_weight, struct task_struct *task, u64 clone_flags)
+{
+	struct bpf_cpumask *local;
+
+	if (!is_test_task())
+		return 0;
+
+	local = create_cpumask();
+	if (!local)
+		return 0;
+
+	if (bpf_cpumask_weight(cast(local)) != 0) {
+		err = 3;
+		goto out;
+	}
+
+	bpf_cpumask_set_cpu(0, local);
+	if (bpf_cpumask_weight(cast(local)) != 1) {
+		err = 4;
+		goto out;
+	}
+
+	/*
+	 * Make sure that adding additional CPUs changes the weight. Test to
+	 * see whether the CPU was set to account for running on UP machines.
+	 */
+	bpf_cpumask_set_cpu(1, local);
+	if (bpf_cpumask_test_cpu(1, cast(local)) && bpf_cpumask_weight(cast(local)) != 2) {
+		err = 5;
+		goto out;
+	}
+
+	bpf_cpumask_clear(local);
+	if (bpf_cpumask_weight(cast(local)) != 0) {
+		err = 6;
+		goto out;
+	}
+out:
+	bpf_cpumask_release(local);
+	return 0;
+}
+
 SEC("tp_btf/task_newtask")
 __success
 int BPF_PROG(test_refcount_null_tracking, struct task_struct *task, u64 clone_flags)