[PATCH v2 4/4] selftests/riscv: Add Zicbop prefetch test - Linux-kselftest-mirror

9 Oct 2025

Add a new selftest under hwprobe/ to verify Zicbop extension behavior.
The test checks:
- That hwprobe correctly reports Zicbop presence and block size.
- That prefetch instructions execute without exception on valid and NULL
  addresses when Zicbop is present.
- That prefetch.{i,r,w} do not trigger SIGILL even when Zicbop is absent,
  since Zicbop instructions are defined as hints.
The test is based on cbo.c but adapted for Zicbop prefetch instructions.
Signed-off-by: Yao Zihong zihong.plct@isrc.iscas.ac.cn
---
 .../testing/selftests/riscv/hwprobe/Makefile  |   5 +-
 .../selftests/riscv/hwprobe/prefetch.c        | 236 ++++++++++++++++++
 2 files changed, 240 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/riscv/hwprobe/prefetch.c

diff --git a/tools/testing/selftests/riscv/hwprobe/Makefile b/tools/testing/selftests/riscv/hwprobe/Makefile
index cec81610a5f2..3c8b8ba7629c 100644
--- a/tools/testing/selftests/riscv/hwprobe/Makefile
+++ b/tools/testing/selftests/riscv/hwprobe/Makefile
@@ -4,7 +4,7 @@
CFLAGS += -I$(top_srcdir)/tools/include
-TEST_GEN_PROGS := hwprobe cbo which-cpus
+TEST_GEN_PROGS := hwprobe cbo which-cpus prefetch
include ../../lib.mk
@@ -16,3 +16,6 @@ $(OUTPUT)/cbo: cbo.c sys_hwprobe.S
$(OUTPUT)/which-cpus: which-cpus.c sys_hwprobe.S
    $(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
+
+$(OUTPUT)/prefetch: prefetch.c sys_hwprobe.S
+	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
diff --git a/tools/testing/selftests/riscv/hwprobe/prefetch.c b/tools/testing/selftests/riscv/hwprobe/prefetch.c
new file mode 100644
index 000000000000..d9ea048325fb
--- /dev/null
+++ b/tools/testing/selftests/riscv/hwprobe/prefetch.c
@@ -0,0 +1,236 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2023 Ventana Micro Systems Inc.
+ * Copyright (c) 2025 PLCT Lab, ISCAS
+ *
+ * Based on tools/testing/selftests/riscv/hwprobe/cbo.c with modifications
+ * for Zicbop prefetch testing.
+ *
+ * Run with 'taskset -c <cpu-list> prefetch' to only execute hwprobe on a
+ * subset of cpus, as well as only executing the tests on those cpus.
+ */
+#define _GNU_SOURCE
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+#include <sched.h>
+#include <signal.h>
+#include <assert.h>
+#include <linux/compiler.h>
+#include <linux/kernel.h>
+#include <asm/ucontext.h>
+
+#include "hwprobe.h"
+#include "../../kselftest.h"
+
+#define MK_PREFETCH(fn) \
+	le32_bswap(0 << 25 | (uint32_t)(fn) << 20 | 10 << 15 | 6 << 12 | 0 << 7 | 19)
+
+static char mem[4096] __aligned(4096) = { [0 ... 4095] = 0xa5 };
+
+static bool illegal;
+
+static void sigill_handler(int sig, siginfo_t *info, void *context)
+{
+	unsigned long *regs = (unsigned long *)&((ucontext_t *)context)->uc_mcontext;
+	uint32_t insn = *(uint32_t *)regs[0];
+
+	assert(insn == MK_PREFETCH(regs[11]));
+
+	illegal = true;
+	regs[0] += 4;
+}
+
+#define prefetch_insn(base, fn)							\
+({										\
+	asm volatile(								\
+	"mv	a0, %0\n"							\
+	"li	a1, %1\n"							\
+	".4byte	%2\n"								\
+	: : "r" (base), "i" (fn), "i" (MK_PREFETCH(fn)) : "a0", "a1", "memory");\
+})
+
+static void prefetch_i(char *base) { prefetch_insn(base, 0); }
+
+static void prefetch_r(char *base) { prefetch_insn(base, 1); }
+
+static void prefetch_w(char *base) { prefetch_insn(base, 3); }
+
+static bool is_power_of_2(__u64 n)
+{
+	return n != 0 && (n & (n - 1)) == 0;
+}
+
+static void test_no_zicbop(void *arg)
+{
+	// Zicbop prefetch.* are HINT instructions.
+	ksft_print_msg("Testing Zicbop instructions\n");
+
+	illegal = false;
+	prefetch_i(&mem[0]);
+	ksft_test_result(!illegal, "No prefetch.i\n");
+
+	illegal = false;
+	prefetch_r(&mem[0]);
+	ksft_test_result(!illegal, "No prefetch.r\n");
+
+	illegal = false;
+	prefetch_w(&mem[0]);
+	ksft_test_result(!illegal, "No prefetch.w\n");
+}
+
+static void test_zicbop(void *arg)
+{
+	struct riscv_hwprobe pair = {
+		.key = RISCV_HWPROBE_KEY_ZICBOP_BLOCK_SIZE,
+	};
+	cpu_set_t *cpus = (cpu_set_t *)arg;
+	__u64 block_size;
+	long rc;
+
+	rc = riscv_hwprobe(&pair, 1, sizeof(cpu_set_t), (unsigned long *)cpus, 0);
+	block_size = pair.value;
+	ksft_test_result(rc == 0 && pair.key == RISCV_HWPROBE_KEY_ZICBOP_BLOCK_SIZE &&
+			 is_power_of_2(block_size), "Zicbop block size\n");
+	ksft_print_msg("Zicbop block size: %llu\n", block_size);
+
+	illegal = false;
+	prefetch_i(&mem[0]);
+	prefetch_r(&mem[0]);
+	prefetch_w(&mem[0]);
+	ksft_test_result(!illegal, "Zicbop prefetch.* on valid address\n");
+
+	illegal = false;
+	prefetch_i(NULL);
+	prefetch_r(NULL);
+	prefetch_w(NULL);
+	ksft_test_result(!illegal, "Zicbop prefetch.* on NULL\n");
+}
+
+static void check_no_zicbop_cpus(cpu_set_t *cpus)
+{
+	struct riscv_hwprobe pair = {
+		.key = RISCV_HWPROBE_KEY_IMA_EXT_0,
+	};
+	cpu_set_t one_cpu;
+	int i = 0, c = 0;
+	long rc;
+
+	while (i++ < CPU_COUNT(cpus)) {
+		while (!CPU_ISSET(c, cpus))
+			++c;
+
+		CPU_ZERO(&one_cpu);
+		CPU_SET(c, &one_cpu);
+
+		rc = riscv_hwprobe(&pair, 1, sizeof(cpu_set_t), (unsigned long *)&one_cpu, 0);
+		assert(rc == 0 && pair.key == RISCV_HWPROBE_KEY_IMA_EXT_0);
+
+		if (pair.value & RISCV_HWPROBE_EXT_ZICBOP)
+			ksft_exit_fail_msg("zicbop is only present on a subset of harts.\n"
+					   "Use taskset to select a set of harts where zicbop\n"
+					   "presence (present or not) is consistent for each hart\n");
+		++c;
+	}
+}
+
+enum {
+	TEST_ZICBOP,
+	TEST_NO_ZICBOP,
+};
+
+enum {
+	HANDLER_SIGILL,
+	HANDLER_SIGSEGV,
+	HANDLER_SIGBUS,
+};
+
+static struct test_info {
+	bool enabled;
+	unsigned int nr_tests;
+	void (*test_fn)(void *arg);
+} tests[] = {
+	[TEST_ZICBOP]		= { .nr_tests = 3, test_zicbop },
+	[TEST_NO_ZICBOP]	= { .nr_tests = 3, test_no_zicbop },
+};
+
+static struct sighandler_info {
+	const char *flag;
+	int sig;
+} handlers[] = {
+	[HANDLER_SIGILL] = { .flag = "--sigill", .sig = SIGILL },
+	[HANDLER_SIGSEGV] = { .flag = "--sigsegv", .sig = SIGSEGV },
+	[HANDLER_SIGBUS] = { .flag = "--sigbus", .sig = SIGBUS },
+};
+
+static bool search_flag(int argc, char **argv, const char *flag)
+{
+	int i;
+
+	for (i = 1; i < argc; i++) {
+		if (!strcmp(argv[i], flag))
+			return true;
+	}
+	return false;
+}
+
+static void install_sigaction(int argc, char **argv)
+{
+	int i, rc;
+	struct sigaction act = {
+		.sa_sigaction = &sigill_handler,
+		.sa_flags = SA_SIGINFO,
+	};
+
+	for (i = 0; i < ARRAY_SIZE(handlers); ++i) {
+		if (search_flag(argc, argv, handlers[i].flag)) {
+			rc = sigaction(handlers[i].sig, &act, NULL);
+			assert(rc == 0);
+		}
+	}
+
+	if (search_flag(argc, argv, handlers[HANDLER_SIGILL].flag))
+		tests[TEST_NO_ZICBOP].enabled = true;
+}
+
+int main(int argc, char **argv)
+{
+	struct riscv_hwprobe pair;
+	unsigned int plan = 0;
+	cpu_set_t cpus;
+	long rc;
+	int i;
+
+	install_sigaction(argc, argv);
+
+	rc = sched_getaffinity(0, sizeof(cpu_set_t), &cpus);
+	assert(rc == 0);
+
+	ksft_print_header();
+
+	pair.key = RISCV_HWPROBE_KEY_IMA_EXT_0;
+	rc = riscv_hwprobe(&pair, 1, sizeof(cpu_set_t), (unsigned long *)&cpus, 0);
+	if (rc < 0)
+		ksft_exit_fail_msg("hwprobe() failed with %ld\n", rc);
+	assert(rc == 0 && pair.key == RISCV_HWPROBE_KEY_IMA_EXT_0);
+
+	if (pair.value & RISCV_HWPROBE_EXT_ZICBOP)
+		tests[TEST_ZICBOP].enabled = true;
+	else
+		check_no_zicbop_cpus(&cpus);
+
+	for (i = 0; i < ARRAY_SIZE(tests); ++i)
+		plan += tests[i].enabled ? tests[i].nr_tests : 0;
+
+	if (plan == 0)
+		ksft_print_msg("No tests enabled.\n");
+	else
+		ksft_set_plan(plan);
+
+	for (i = 0; i < ARRAY_SIZE(tests); ++i) {
+		if (tests[i].enabled)
+			tests[i].test_fn(&cpus);
+	}
+
+	ksft_finished();
+}
-- 
2.47.2



    