selftests/bpf: Add test for bpf_get_smp_processor_id

Add a test which checks on each CPU that the bpf_get_smp_processor_id
BPF helper is returning the correct CPU number.

Signed-off-by: Maxim Khmelevskii <max@linux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/bpf/20260703125648.919196-6-max@linux.ibm.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

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

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include "bpf/libbpf_internal.h"
+#include "get_smp_processor_id.skel.h"
+
+void test_get_smp_processor_id(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, opts,
+		    .flags = BPF_F_TEST_RUN_ON_CPU,
+		    .cpu = 0,
+	);
+	struct get_smp_processor_id *skel;
+	int prog_fd, err, online_cpu_nr, i;
+	bool *online = NULL;
+
+	err = parse_cpu_mask_file("/sys/devices/system/cpu/online",
+				  &online, &online_cpu_nr);
+	if (!ASSERT_OK(err, "parse_cpu_mask_file"))
+		return;
+
+	skel = get_smp_processor_id__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "get_smp_processor_id__open_and_load"))
+		goto cleanup;
+
+	prog_fd = bpf_program__fd(skel->progs.call_bpf_get_smp_processor_id);
+
+	for (i = 0; i < online_cpu_nr; i++) {
+		if (!online[i])
+			continue;
+
+		opts.cpu = i;
+		skel->bss->cpu_nr_result = -1;
+
+		err = bpf_prog_test_run_opts(prog_fd, &opts);
+		if (!ASSERT_OK(err, "bpf_prog_test_run_opts"))
+			goto cleanup;
+
+		ASSERT_EQ(skel->bss->cpu_nr_result, opts.cpu, "cpu_nr_result");
+	}
+
+cleanup:
+	free(online);
+	get_smp_processor_id__destroy(skel);
+}

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

@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+__u64 cpu_nr_result;
+
+SEC("raw_tp")
+void call_bpf_get_smp_processor_id(void)
+{
+	register __u64 r0 asm("r0") = -1;
+	asm volatile ("call %[bpf_get_smp_processor_id];"
+		      : "+r"(r0)
+		      : __imm(bpf_get_smp_processor_id)
+		      : "r1", "r2", "r3", "r4", "r5", "memory");
+	cpu_nr_result = r0;
+}
+
+char _license[] SEC("license") = "GPL";