[linux-block.git] / Documentation / bpf / cpumasks.rst

.. SPDX-License-Identifier: GPL-2.0

.. _cpumasks-header-label:

==================
BPF cpumask kfuncs
==================

1. Introduction
===============

``struct cpumask`` is a bitmap data structure in the kernel whose indices
reflect the CPUs on the system. Commonly, cpumasks are used to track which CPUs
a task is affinitized to, but they can also be used to e.g. track which cores
are associated with a scheduling domain, which cores on a machine are idle,
etc.

BPF provides programs with a set of :ref:`kfuncs-header-label` that can be
used to allocate, mutate, query, and free cpumasks.

2. BPF cpumask objects
======================

There are two different types of cpumasks that can be used by BPF programs.

2.1 ``struct bpf_cpumask *``
----------------------------

``struct bpf_cpumask *`` is a cpumask that is allocated by BPF, on behalf of a
BPF program, and whose lifecycle is entirely controlled by BPF. These cpumasks
are RCU-protected, can be mutated, can be used as kptrs, and can be safely cast
to a ``struct cpumask *``.

2.1.1 ``struct bpf_cpumask *`` lifecycle
----------------------------------------

A ``struct bpf_cpumask *`` is allocated, acquired, and released, using the
following functions:

.. kernel-doc:: kernel/bpf/cpumask.c
  :identifiers: bpf_cpumask_create

.. kernel-doc:: kernel/bpf/cpumask.c
  :identifiers: bpf_cpumask_acquire

.. kernel-doc:: kernel/bpf/cpumask.c
  :identifiers: bpf_cpumask_release

For example:

.. code-block:: c

        struct cpumask_map_value {
                struct bpf_cpumask __kptr * cpumask;
        };

        struct array_map {
                __uint(type, BPF_MAP_TYPE_ARRAY);
                __type(key, int);
                __type(value, struct cpumask_map_value);
                __uint(max_entries, 65536);
        } cpumask_map SEC(".maps");

        static int cpumask_map_insert(struct bpf_cpumask *mask, u32 pid)
        {
                struct cpumask_map_value local, *v;
                long status;
                struct bpf_cpumask *old;
                u32 key = pid;

                local.cpumask = NULL;
                status = bpf_map_update_elem(&cpumask_map, &key, &local, 0);
                if (status) {
                        bpf_cpumask_release(mask);
                        return status;
                }

                v = bpf_map_lookup_elem(&cpumask_map, &key);
                if (!v) {
                        bpf_cpumask_release(mask);
                        return -ENOENT;
                }

                old = bpf_kptr_xchg(&v->cpumask, mask);
                if (old)
                        bpf_cpumask_release(old);

                return 0;
        }

        /**
         * A sample tracepoint showing how a task's cpumask can be queried and
         * recorded as a kptr.
         */
        SEC("tp_btf/task_newtask")
        int BPF_PROG(record_task_cpumask, struct task_struct *task, u64 clone_flags)
        {
                struct bpf_cpumask *cpumask;
                int ret;

                cpumask = bpf_cpumask_create();
                if (!cpumask)
                        return -ENOMEM;

                if (!bpf_cpumask_full(task->cpus_ptr))
                        bpf_printk("task %s has CPU affinity", task->comm);

                bpf_cpumask_copy(cpumask, task->cpus_ptr);
                return cpumask_map_insert(cpumask, task->pid);
        }

----

2.1.1 ``struct bpf_cpumask *`` as kptrs
---------------------------------------

As mentioned and illustrated above, these ``struct bpf_cpumask *`` objects can
also be stored in a map and used as kptrs. If a ``struct bpf_cpumask *`` is in
a map, the reference can be removed from the map with bpf_kptr_xchg(), or
opportunistically acquired using RCU:

.. code-block:: c

	/* struct containing the struct bpf_cpumask kptr which is stored in the map. */
	struct cpumasks_kfunc_map_value {
		struct bpf_cpumask __kptr * bpf_cpumask;
	};

	/* The map containing struct cpumasks_kfunc_map_value entries. */
	struct {
		__uint(type, BPF_MAP_TYPE_ARRAY);
		__type(key, int);
		__type(value, struct cpumasks_kfunc_map_value);
		__uint(max_entries, 1);
	} cpumasks_kfunc_map SEC(".maps");

	/* ... */

	/**
	 * A simple example tracepoint program showing how a
	 * struct bpf_cpumask * kptr that is stored in a map can
	 * be passed to kfuncs using RCU protection.
	 */
	SEC("tp_btf/cgroup_mkdir")
	int BPF_PROG(cgrp_ancestor_example, struct cgroup *cgrp, const char *path)
	{
		struct bpf_cpumask *kptr;
		struct cpumasks_kfunc_map_value *v;
		u32 key = 0;

		/* Assume a bpf_cpumask * kptr was previously stored in the map. */
		v = bpf_map_lookup_elem(&cpumasks_kfunc_map, &key);
		if (!v)
			return -ENOENT;

		bpf_rcu_read_lock();
		/* Acquire a reference to the bpf_cpumask * kptr that's already stored in the map. */
		kptr = v->cpumask;
		if (!kptr) {
			/* If no bpf_cpumask was present in the map, it's because
			 * we're racing with another CPU that removed it with
			 * bpf_kptr_xchg() between the bpf_map_lookup_elem()
			 * above, and our load of the pointer from the map.
			 */
			bpf_rcu_read_unlock();
			return -EBUSY;
		}

		bpf_cpumask_setall(kptr);
		bpf_rcu_read_unlock();

		return 0;
	}

----

2.2 ``struct cpumask``
----------------------

``struct cpumask`` is the object that actually contains the cpumask bitmap
being queried, mutated, etc. A ``struct bpf_cpumask`` wraps a ``struct
cpumask``, which is why it's safe to cast it as such (note however that it is
**not** safe to cast a ``struct cpumask *`` to a ``struct bpf_cpumask *``, and
the verifier will reject any program that tries to do so).

As we'll see below, any kfunc that mutates its cpumask argument will take a
``struct bpf_cpumask *`` as that argument. Any argument that simply queries the
cpumask will instead take a ``struct cpumask *``.

3. cpumask kfuncs
=================

Above, we described the kfuncs that can be used to allocate, acquire, release,
etc a ``struct bpf_cpumask *``. This section of the document will describe the
kfuncs for mutating and querying cpumasks.

3.1 Mutating cpumasks
---------------------

Some cpumask kfuncs are "read-only" in that they don't mutate any of their
arguments, whereas others mutate at least one argument (which means that the
argument must be a ``struct bpf_cpumask *``, as described above).

This section will describe all of the cpumask kfuncs which mutate at least one
argument. :ref:`cpumasks-querying-label` below describes the read-only kfuncs.

3.1.1 Setting and clearing CPUs
-------------------------------

bpf_cpumask_set_cpu() and bpf_cpumask_clear_cpu() can be used to set and clear
a CPU in a ``struct bpf_cpumask`` respectively:

.. kernel-doc:: kernel/bpf/cpumask.c
   :identifiers: bpf_cpumask_set_cpu bpf_cpumask_clear_cpu

These kfuncs are pretty straightforward, and can be used, for example, as
follows:

.. code-block:: c

        /**
         * A sample tracepoint showing how a cpumask can be queried.
         */
        SEC("tp_btf/task_newtask")
        int BPF_PROG(test_set_clear_cpu, struct task_struct *task, u64 clone_flags)
        {
                struct bpf_cpumask *cpumask;

                cpumask = bpf_cpumask_create();
                if (!cpumask)
                        return -ENOMEM;

                bpf_cpumask_set_cpu(0, cpumask);
                if (!bpf_cpumask_test_cpu(0, cast(cpumask)))
                        /* Should never happen. */
                        goto release_exit;

                bpf_cpumask_clear_cpu(0, cpumask);
                if (bpf_cpumask_test_cpu(0, cast(cpumask)))
                        /* Should never happen. */
                        goto release_exit;

                /* struct cpumask * pointers such as task->cpus_ptr can also be queried. */
                if (bpf_cpumask_test_cpu(0, task->cpus_ptr))
                        bpf_printk("task %s can use CPU %d", task->comm, 0);

        release_exit:
                bpf_cpumask_release(cpumask);
                return 0;
        }

----

bpf_cpumask_test_and_set_cpu() and bpf_cpumask_test_and_clear_cpu() are
complementary kfuncs that allow callers to atomically test and set (or clear)
CPUs:

.. kernel-doc:: kernel/bpf/cpumask.c
   :identifiers: bpf_cpumask_test_and_set_cpu bpf_cpumask_test_and_clear_cpu

----

We can also set and clear entire ``struct bpf_cpumask *`` objects in one
operation using bpf_cpumask_setall() and bpf_cpumask_clear():

.. kernel-doc:: kernel/bpf/cpumask.c
   :identifiers: bpf_cpumask_setall bpf_cpumask_clear

3.1.2 Operations between cpumasks
---------------------------------

In addition to setting and clearing individual CPUs in a single cpumask,
callers can also perform bitwise operations between multiple cpumasks using
bpf_cpumask_and(), bpf_cpumask_or(), and bpf_cpumask_xor():

.. kernel-doc:: kernel/bpf/cpumask.c
   :identifiers: bpf_cpumask_and bpf_cpumask_or bpf_cpumask_xor

The following is an example of how they may be used. Note that some of the
kfuncs shown in this example will be covered in more detail below.

.. code-block:: c

        /**
         * A sample tracepoint showing how a cpumask can be mutated using
           bitwise operators (and queried).
         */
        SEC("tp_btf/task_newtask")
        int BPF_PROG(test_and_or_xor, struct task_struct *task, u64 clone_flags)
        {
                struct bpf_cpumask *mask1, *mask2, *dst1, *dst2;

                mask1 = bpf_cpumask_create();
                if (!mask1)
                        return -ENOMEM;

                mask2 = bpf_cpumask_create();
                if (!mask2) {
                        bpf_cpumask_release(mask1);
                        return -ENOMEM;
                }

                // ...Safely create the other two masks... */

                bpf_cpumask_set_cpu(0, mask1);
                bpf_cpumask_set_cpu(1, mask2);
                bpf_cpumask_and(dst1, (const struct cpumask *)mask1, (const struct cpumask *)mask2);
                if (!bpf_cpumask_empty((const struct cpumask *)dst1))
                        /* Should never happen. */
                        goto release_exit;

                bpf_cpumask_or(dst1, (const struct cpumask *)mask1, (const struct cpumask *)mask2);
                if (!bpf_cpumask_test_cpu(0, (const struct cpumask *)dst1))
                        /* Should never happen. */
                        goto release_exit;

                if (!bpf_cpumask_test_cpu(1, (const struct cpumask *)dst1))
                        /* Should never happen. */
                        goto release_exit;

                bpf_cpumask_xor(dst2, (const struct cpumask *)mask1, (const struct cpumask *)mask2);
                if (!bpf_cpumask_equal((const struct cpumask *)dst1,
                                       (const struct cpumask *)dst2))
                        /* Should never happen. */
                        goto release_exit;

         release_exit:
                bpf_cpumask_release(mask1);
                bpf_cpumask_release(mask2);
                bpf_cpumask_release(dst1);
                bpf_cpumask_release(dst2);
                return 0;
        }

----

The contents of an entire cpumask may be copied to another using
bpf_cpumask_copy():

.. kernel-doc:: kernel/bpf/cpumask.c
   :identifiers: bpf_cpumask_copy

----

.. _cpumasks-querying-label:

3.2 Querying cpumasks
---------------------

In addition to the above kfuncs, there is also a set of read-only kfuncs that
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_test_cpu

.. kernel-doc:: kernel/bpf/cpumask.c
   :identifiers: bpf_cpumask_equal bpf_cpumask_intersects bpf_cpumask_subset
                 bpf_cpumask_empty bpf_cpumask_full

.. kernel-doc:: kernel/bpf/cpumask.c
   :identifiers: bpf_cpumask_any bpf_cpumask_any_and

----

Some example usages of these querying kfuncs were shown above. We will not
replicate those exmaples here. Note, however, that all of the aforementioned
kfuncs are tested in `tools/testing/selftests/bpf/progs/cpumask_success.c`_, so
please take a look there if you're looking for more examples of how they can be
used.

.. _tools/testing/selftests/bpf/progs/cpumask_success.c:
   https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/progs/cpumask_success.c


4. Adding BPF cpumask kfuncs
============================

The set of supported BPF cpumask kfuncs are not (yet) a 1-1 match with the
cpumask operations in include/linux/cpumask.h. Any of those cpumask operations
could easily be encapsulated in a new kfunc if and when required. If you'd like
to support a new cpumask operation, please feel free to submit a patch. If you
do add a new cpumask kfunc, please document it here, and add any relevant
selftest testcases to the cpumask selftest suite.
Commit	Line	Data
bdbda395 DV	1	.. SPDX-License-Identifier: GPL-2.0
	2
	3	.. _cpumasks-header-label:
	4
	5	==================
	6	BPF cpumask kfuncs
	7	==================
	8
	9	1. Introduction
	10	===============
	11
	12	``struct cpumask`` is a bitmap data structure in the kernel whose indices
	13	reflect the CPUs on the system. Commonly, cpumasks are used to track which CPUs
	14	a task is affinitized to, but they can also be used to e.g. track which cores
	15	are associated with a scheduling domain, which cores on a machine are idle,
	16	etc.
	17
	18	BPF provides programs with a set of :ref:`kfuncs-header-label` that can be
	19	used to allocate, mutate, query, and free cpumasks.
	20
	21	2. BPF cpumask objects
	22	======================
	23
	24	There are two different types of cpumasks that can be used by BPF programs.
	25
	26	2.1 ``struct bpf_cpumask *``
	27	----------------------------
	28
	29	``struct bpf_cpumask *`` is a cpumask that is allocated by BPF, on behalf of a
	30	BPF program, and whose lifecycle is entirely controlled by BPF. These cpumasks
	31	are RCU-protected, can be mutated, can be used as kptrs, and can be safely cast
	32	to a ``struct cpumask *``.
	33
	34	2.1.1 ``struct bpf_cpumask *`` lifecycle
	35	----------------------------------------
	36
	37	A ``struct bpf_cpumask *`` is allocated, acquired, and released, using the
	38	following functions:
	39
	40	.. kernel-doc:: kernel/bpf/cpumask.c
	41	:identifiers: bpf_cpumask_create
	42
	43	.. kernel-doc:: kernel/bpf/cpumask.c
	44	:identifiers: bpf_cpumask_acquire
	45
	46	.. kernel-doc:: kernel/bpf/cpumask.c
	47	:identifiers: bpf_cpumask_release
	48
	49	For example:
	50
	51	.. code-block:: c
	52
	53	struct cpumask_map_value {
03b77e17	54	struct bpf_cpumask __kptr * cpumask;
bdbda395 DV	55	};
	56
	57	struct array_map {
	58	__uint(type, BPF_MAP_TYPE_ARRAY);
	59	__type(key, int);
	60	__type(value, struct cpumask_map_value);
	61	__uint(max_entries, 65536);
	62	} cpumask_map SEC(".maps");
	63
	64	static int cpumask_map_insert(struct bpf_cpumask *mask, u32 pid)
	65	{
	66	struct cpumask_map_value local, *v;
	67	long status;
	68	struct bpf_cpumask *old;
	69	u32 key = pid;
	70
	71	local.cpumask = NULL;
	72	status = bpf_map_update_elem(&cpumask_map, &key, &local, 0);
	73	if (status) {
	74	bpf_cpumask_release(mask);
	75	return status;
	76	}
	77
	78	v = bpf_map_lookup_elem(&cpumask_map, &key);
	79	if (!v) {
	80	bpf_cpumask_release(mask);
	81	return -ENOENT;
	82	}
	83
	84	old = bpf_kptr_xchg(&v->cpumask, mask);
	85	if (old)
	86	bpf_cpumask_release(old);
	87
	88	return 0;
	89	}
	90
	91	/**
	92	* A sample tracepoint showing how a task's cpumask can be queried and
	93	* recorded as a kptr.
	94	*/
	95	SEC("tp_btf/task_newtask")
	96	int BPF_PROG(record_task_cpumask, struct task_struct *task, u64 clone_flags)
	97	{
	98	struct bpf_cpumask *cpumask;
	99	int ret;
	100
	101	cpumask = bpf_cpumask_create();
	102	if (!cpumask)
	103	return -ENOMEM;
	104
	105	if (!bpf_cpumask_full(task->cpus_ptr))
	106	bpf_printk("task %s has CPU affinity", task->comm);
	107
	108	bpf_cpumask_copy(cpumask, task->cpus_ptr);
	109	return cpumask_map_insert(cpumask, task->pid);
	110	}
	111
	112	----
	113
	114	2.1.1 ``struct bpf_cpumask *`` as kptrs
	115	---------------------------------------
	116
	117	As mentioned and illustrated above, these ``struct bpf_cpumask *`` objects can
	118	also be stored in a map and used as kptrs. If a ``struct bpf_cpumask *`` is in
119	a map, the reference can be removed from the map with bpf_kptr_xchg(), or
fec2c6d1	120	opportunistically acquired using RCU:
bdbda395 DV	121
	122	.. code-block:: c
	123
	124	/* struct containing the struct bpf_cpumask kptr which is stored in the map. */
	125	struct cpumasks_kfunc_map_value {
03b77e17	126	struct bpf_cpumask __kptr * bpf_cpumask;
bdbda395 DV	127	};
	128
	129	/* The map containing struct cpumasks_kfunc_map_value entries. */
	130	struct {
	131	__uint(type, BPF_MAP_TYPE_ARRAY);
	132	__type(key, int);
	133	__type(value, struct cpumasks_kfunc_map_value);
	134	__uint(max_entries, 1);
	135	} cpumasks_kfunc_map SEC(".maps");
	136
	137	/* ... */
	138
	139	/**
	140	* A simple example tracepoint program showing how a
	141	* struct bpf_cpumask * kptr that is stored in a map can
fec2c6d1	142	* be passed to kfuncs using RCU protection.
bdbda395 DV	143	*/
	144	SEC("tp_btf/cgroup_mkdir")
	145	int BPF_PROG(cgrp_ancestor_example, struct cgroup cgrp, const char path)
	146	{
	147	struct bpf_cpumask *kptr;
	148	struct cpumasks_kfunc_map_value *v;
	149	u32 key = 0;
	150
	151	/* Assume a bpf_cpumask * kptr was previously stored in the map. */
	152	v = bpf_map_lookup_elem(&cpumasks_kfunc_map, &key);
	153	if (!v)
	154	return -ENOENT;
	155
fec2c6d1	156	bpf_rcu_read_lock();
bdbda395	157	/* Acquire a reference to the bpf_cpumask * kptr that's already stored in the map. */
fec2c6d1 DV	158	kptr = v->cpumask;
fec2c6d1 DV	159	if (!kptr) {
bdbda395 DV	160	/* If no bpf_cpumask was present in the map, it's because
	161	* we're racing with another CPU that removed it with
	162	* bpf_kptr_xchg() between the bpf_map_lookup_elem()
fec2c6d1	163	* above, and our load of the pointer from the map.
bdbda395	164	*/
fec2c6d1	165	bpf_rcu_read_unlock();
bdbda395	166	return -EBUSY;
fec2c6d1	167	}
bdbda395	168
fec2c6d1 DV	169	bpf_cpumask_setall(kptr);
fec2c6d1 DV	170	bpf_rcu_read_unlock();
bdbda395 DV	171
	172	return 0;
	173	}
	174
	175	----
	176
	177	2.2 ``struct cpumask``
	178	----------------------
	179
	180	``struct cpumask`` is the object that actually contains the cpumask bitmap
	181	being queried, mutated, etc. A ``struct bpf_cpumask`` wraps a ``struct
	182	cpumask``, which is why it's safe to cast it as such (note however that it is
	183	not safe to cast a ``struct cpumask `` to a ``struct bpf_cpumask ``, and
	184	the verifier will reject any program that tries to do so).
	185
	186	As we'll see below, any kfunc that mutates its cpumask argument will take a
	187	``struct bpf_cpumask *`` as that argument. Any argument that simply queries the
	188	cpumask will instead take a ``struct cpumask *``.
	189
	190	3. cpumask kfuncs
	191	=================
	192
	193	Above, we described the kfuncs that can be used to allocate, acquire, release,
	194	etc a ``struct bpf_cpumask *``. This section of the document will describe the
	195	kfuncs for mutating and querying cpumasks.
	196
	197	3.1 Mutating cpumasks
	198	---------------------
	199
	200	Some cpumask kfuncs are "read-only" in that they don't mutate any of their
	201	arguments, whereas others mutate at least one argument (which means that the
	202	argument must be a ``struct bpf_cpumask *``, as described above).
	203
	204	This section will describe all of the cpumask kfuncs which mutate at least one
	205	argument. :ref:`cpumasks-querying-label` below describes the read-only kfuncs.
	206
	207	3.1.1 Setting and clearing CPUs
	208	-------------------------------
	209
	210	bpf_cpumask_set_cpu() and bpf_cpumask_clear_cpu() can be used to set and clear
	211	a CPU in a ``struct bpf_cpumask`` respectively:
	212
	213	.. kernel-doc:: kernel/bpf/cpumask.c
	214	:identifiers: bpf_cpumask_set_cpu bpf_cpumask_clear_cpu
	215
	216	These kfuncs are pretty straightforward, and can be used, for example, as
	217	follows:
	218
	219	.. code-block:: c
	220
	221	/**
	222	* A sample tracepoint showing how a cpumask can be queried.
	223	*/
	224	SEC("tp_btf/task_newtask")
	225	int BPF_PROG(test_set_clear_cpu, struct task_struct *task, u64 clone_flags)
	226	{
	227	struct bpf_cpumask *cpumask;
	228
	229	cpumask = bpf_cpumask_create();
	230	if (!cpumask)
	231	return -ENOMEM;
	232
	233	bpf_cpumask_set_cpu(0, cpumask);
	234	if (!bpf_cpumask_test_cpu(0, cast(cpumask)))
235	/* Should never happen. */
236	goto release_exit;
237
238	bpf_cpumask_clear_cpu(0, cpumask);
239	if (bpf_cpumask_test_cpu(0, cast(cpumask)))
240	/* Should never happen. */
241	goto release_exit;
242
243	/* struct cpumask * pointers such as task->cpus_ptr can also be queried. */
244	if (bpf_cpumask_test_cpu(0, task->cpus_ptr))
245	bpf_printk("task %s can use CPU %d", task->comm, 0);
246
247	release_exit:
248	bpf_cpumask_release(cpumask);
249	return 0;
250	}
251
252	----
253
254	bpf_cpumask_test_and_set_cpu() and bpf_cpumask_test_and_clear_cpu() are
255	complementary kfuncs that allow callers to atomically test and set (or clear)
256	CPUs:
257
258	.. kernel-doc:: kernel/bpf/cpumask.c
259	:identifiers: bpf_cpumask_test_and_set_cpu bpf_cpumask_test_and_clear_cpu
260
261	----
262
263	We can also set and clear entire ``struct bpf_cpumask *`` objects in one
264	operation using bpf_cpumask_setall() and bpf_cpumask_clear():
265
266	.. kernel-doc:: kernel/bpf/cpumask.c
267	:identifiers: bpf_cpumask_setall bpf_cpumask_clear
268
269	3.1.2 Operations between cpumasks
270	---------------------------------
271
272	In addition to setting and clearing individual CPUs in a single cpumask,
273	callers can also perform bitwise operations between multiple cpumasks using
274	bpf_cpumask_and(), bpf_cpumask_or(), and bpf_cpumask_xor():
275
276	.. kernel-doc:: kernel/bpf/cpumask.c
277	:identifiers: bpf_cpumask_and bpf_cpumask_or bpf_cpumask_xor
278
279	The following is an example of how they may be used. Note that some of the
280	kfuncs shown in this example will be covered in more detail below.
281
282	.. code-block:: c
283
284	/**
285	* A sample tracepoint showing how a cpumask can be mutated using
286	bitwise operators (and queried).
287	*/
288	SEC("tp_btf/task_newtask")
289	int BPF_PROG(test_and_or_xor, struct task_struct *task, u64 clone_flags)
290	{
291	struct bpf_cpumask mask1, mask2, dst1, dst2;
292
293	mask1 = bpf_cpumask_create();
294	if (!mask1)
295	return -ENOMEM;
296
297	mask2 = bpf_cpumask_create();
298	if (!mask2) {
299	bpf_cpumask_release(mask1);
300	return -ENOMEM;
301	}
302
303	// ...Safely create the other two masks... */
304
305	bpf_cpumask_set_cpu(0, mask1);
306	bpf_cpumask_set_cpu(1, mask2);
307	bpf_cpumask_and(dst1, (const struct cpumask )mask1, (const struct cpumask )mask2);
308	if (!bpf_cpumask_empty((const struct cpumask *)dst1))
309	/* Should never happen. */
310	goto release_exit;
311
312	bpf_cpumask_or(dst1, (const struct cpumask )mask1, (const struct cpumask )mask2);
313	if (!bpf_cpumask_test_cpu(0, (const struct cpumask *)dst1))
314	/* Should never happen. */
315	goto release_exit;
316
317	if (!bpf_cpumask_test_cpu(1, (const struct cpumask *)dst1))
318	/* Should never happen. */
319	goto release_exit;
320
321	bpf_cpumask_xor(dst2, (const struct cpumask )mask1, (const struct cpumask )mask2);
322	if (!bpf_cpumask_equal((const struct cpumask *)dst1,
323	(const struct cpumask *)dst2))
324	/* Should never happen. */
325	goto release_exit;
326
327	release_exit:
328	bpf_cpumask_release(mask1);
329	bpf_cpumask_release(mask2);
330	bpf_cpumask_release(dst1);
331	bpf_cpumask_release(dst2);
332	return 0;
333	}
334
335	----
336
337	The contents of an entire cpumask may be copied to another using
338	bpf_cpumask_copy():
339
340	.. kernel-doc:: kernel/bpf/cpumask.c
341	:identifiers: bpf_cpumask_copy
342
343	----
344
345	.. _cpumasks-querying-label:
346
347	3.2 Querying cpumasks
348	---------------------
349
350	In addition to the above kfuncs, there is also a set of read-only kfuncs that
351	can be used to query the contents of cpumasks.
352
353	.. kernel-doc:: kernel/bpf/cpumask.c
354	:identifiers: bpf_cpumask_first bpf_cpumask_first_zero bpf_cpumask_test_cpu
355
356	.. kernel-doc:: kernel/bpf/cpumask.c
357	:identifiers: bpf_cpumask_equal bpf_cpumask_intersects bpf_cpumask_subset
358	bpf_cpumask_empty bpf_cpumask_full
359
360	.. kernel-doc:: kernel/bpf/cpumask.c
361	:identifiers: bpf_cpumask_any bpf_cpumask_any_and
362
363	----
364
365	Some example usages of these querying kfuncs were shown above. We will not
366	replicate those exmaples here. Note, however, that all of the aforementioned
367	kfuncs are tested in `tools/testing/selftests/bpf/progs/cpumask_success.c`_, so
368	please take a look there if you're looking for more examples of how they can be
369	used.
370
371	.. _tools/testing/selftests/bpf/progs/cpumask_success.c:
372	https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/tools/testing/selftests/bpf/progs/cpumask_success.c
373
374
375	4. Adding BPF cpumask kfuncs
376	============================
377
378	The set of supported BPF cpumask kfuncs are not (yet) a 1-1 match with the
379	cpumask operations in include/linux/cpumask.h. Any of those cpumask operations
380	could easily be encapsulated in a new kfunc if and when required. If you'd like
381	to support a new cpumask operation, please feel free to submit a patch. If you
382	do add a new cpumask kfunc, please document it here, and add any relevant
383	selftest testcases to the cpumask selftest suite.