kselftest/arm64: Add tests for TPIDR2

The Scalable Matrix Extension adds a new system register TPIDR2 intended to
be used by libc for its own thread specific use, add some kselftests which
exercise the ABI for it.

Since this test should with some adjustment work for TPIDR and any other
similar registers added in future add tests for it in a separate
directory rather than placing it with the other floating point tests,
nothing existing looked suitable so I created a new test directory
called "abi".

Since this feature is intended to be used by libc the test is built as
freestanding code using nolibc so we don't end up with the test program
and libc both trying to manage the register simultaneously and
distrupting each other. As a result of being written using nolibc rather
than using hwcaps to identify if SME is available in the system we check
for the default SME vector length configuration in proc, adding hwcap
support to nolibc seems like disproportionate effort and didn't feel
entirely idiomatic for what nolibc is trying to do.
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220419112247.711548-31-broonie@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/abi/.gitignore

 syscall-abi
+tpidr2

tools/testing/selftests/arm64/abi/Makefile

 # SPDX-License-Identifier: GPL-2.0
 # Copyright (C) 2021 ARM Limited
 
-TEST_GEN_PROGS := syscall-abi
+TEST_GEN_PROGS := syscall-abi tpidr2
 
 include ../../lib.mk
 
 $(OUTPUT)/syscall-abi: syscall-abi.c syscall-abi-asm.S
+
+# Build with nolibc since TPIDR2 is intended to be actively managed by
+# libc and we're trying to test the functionality that it depends on here.
+$(OUTPUT)/tpidr2: tpidr2.c
+	$(CC) -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib \
+		-static -include ../../../../include/nolibc/nolibc.h \
+		-ffreestanding -Wall $^ -o $@ -lgcc

tools/testing/selftests/arm64/abi/tpidr2.c

+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/sched.h>
+#include <linux/wait.h>
+
+#define SYS_TPIDR2 "S3_3_C13_C0_5"
+
+#define EXPECTED_TESTS 5
+
+static void putstr(const char *str)
+{
+	write(1, str, strlen(str));
+}
+
+static void putnum(unsigned int num)
+{
+	char c;
+
+	if (num / 10)
+		putnum(num / 10);
+
+	c = '0' + (num % 10);
+	write(1, &c, 1);
+}
+
+static int tests_run;
+static int tests_passed;
+static int tests_failed;
+static int tests_skipped;
+
+static void set_tpidr2(uint64_t val)
+{
+	asm volatile (
+		"msr	" SYS_TPIDR2 ", %0\n"
+		:
+		: "r"(val)
+		: "cc");
+}
+
+static uint64_t get_tpidr2(void)
+{
+	uint64_t val;
+
+	asm volatile (
+		"mrs	%0, " SYS_TPIDR2 "\n"
+		: "=r"(val)
+		:
+		: "cc");
+
+	return val;
+}
+
+static void print_summary(void)
+{
+	if (tests_passed + tests_failed + tests_skipped != EXPECTED_TESTS)
+		putstr("# UNEXPECTED TEST COUNT: ");
+
+	putstr("# Totals: pass:");
+	putnum(tests_passed);
+	putstr(" fail:");
+	putnum(tests_failed);
+	putstr(" xfail:0 xpass:0 skip:");
+	putnum(tests_skipped);
+	putstr(" error:0\n");
+}
+
+/* Processes should start with TPIDR2 == 0 */
+static int default_value(void)
+{
+	return get_tpidr2() == 0;
+}
+
+/* If we set TPIDR2 we should read that value */
+static int write_read(void)
+{
+	set_tpidr2(getpid());
+
+	return getpid() == get_tpidr2();
+}
+
+/* If we set a value we should read the same value after scheduling out */
+static int write_sleep_read(void)
+{
+	set_tpidr2(getpid());
+
+	msleep(100);
+
+	return getpid() == get_tpidr2();
+}
+
+/*
+ * If we fork the value in the parent should be unchanged and the
+ * child should start with the same value and be able to set its own
+ * value.
+ */
+static int write_fork_read(void)
+{
+	pid_t newpid, waiting, oldpid;
+	int status;
+
+	set_tpidr2(getpid());
+
+	oldpid = getpid();
+	newpid = fork();
+	if (newpid == 0) {
+		/* In child */
+		if (get_tpidr2() != oldpid) {
+			putstr("# TPIDR2 changed in child: ");
+			putnum(get_tpidr2());
+			putstr("\n");
+			exit(0);
+		}
+
+		set_tpidr2(getpid());
+		if (get_tpidr2() == getpid()) {
+			exit(1);
+		} else {
+			putstr("# Failed to set TPIDR2 in child\n");
+			exit(0);
+		}
+	}
+	if (newpid < 0) {
+		putstr("# fork() failed: -");
+		putnum(-newpid);
+		putstr("\n");
+		return 0;
+	}
+
+	for (;;) {
+		waiting = waitpid(newpid, &status, 0);
+
+		if (waiting < 0) {
+			if (errno == EINTR)
+				continue;
+			putstr("# waitpid() failed: ");
+			putnum(errno);
+			putstr("\n");
+			return 0;
+		}
+		if (waiting != newpid) {
+			putstr("# waitpid() returned wrong PID\n");
+			return 0;
+		}
+
+		if (!WIFEXITED(status)) {
+			putstr("# child did not exit\n");
+			return 0;
+		}
+
+		if (getpid() != get_tpidr2()) {
+			putstr("# TPIDR2 corrupted in parent\n");
+			return 0;
+		}
+
+		return WEXITSTATUS(status);
+	}
+}
+
+/*
+ * sys_clone() has a lot of per architecture variation so just define
+ * it here rather than adding it to nolibc, plus the raw API is a
+ * little more convenient for this test.
+ */
+static int sys_clone(unsigned long clone_flags, unsigned long newsp,
+		     int *parent_tidptr, unsigned long tls,
+		     int *child_tidptr)
+{
+	return my_syscall5(__NR_clone, clone_flags, newsp, parent_tidptr, tls,
+			   child_tidptr);
+}
+
+/*
+ * If we clone with CLONE_SETTLS then the value in the parent should
+ * be unchanged and the child should start with zero and be able to
+ * set its own value.
+ */
+static int write_clone_read(void)
+{
+	int parent_tid, child_tid;
+	pid_t parent, waiting;
+	int ret, status;
+
+	parent = getpid();
+	set_tpidr2(parent);
+
+	ret = sys_clone(CLONE_SETTLS, 0, &parent_tid, 0, &child_tid);
+	if (ret == -1) {
+		putstr("# clone() failed\n");
+		putnum(errno);
+		putstr("\n");
+		return 0;
+	}
+
+	if (ret == 0) {
+		/* In child */
+		if (get_tpidr2() != 0) {
+			putstr("# TPIDR2 non-zero in child: ");
+			putnum(get_tpidr2());
+			putstr("\n");
+			exit(0);
+		}
+
+		if (gettid() == 0)
+			putstr("# Child TID==0\n");
+		set_tpidr2(gettid());
+		if (get_tpidr2() == gettid()) {
+			exit(1);
+		} else {
+			putstr("# Failed to set TPIDR2 in child\n");
+			exit(0);
+		}
+	}
+
+	for (;;) {
+		waiting = wait4(ret, &status, __WCLONE, NULL);
+
+		if (waiting < 0) {
+			if (errno == EINTR)
+				continue;
+			putstr("# wait4() failed: ");
+			putnum(errno);
+			putstr("\n");
+			return 0;
+		}
+		if (waiting != ret) {
+			putstr("# wait4() returned wrong PID ");
+			putnum(waiting);
+			putstr("\n");
+			return 0;
+		}
+
+		if (!WIFEXITED(status)) {
+			putstr("# child did not exit\n");
+			return 0;
+		}
+
+		if (parent != get_tpidr2()) {
+			putstr("# TPIDR2 corrupted in parent\n");
+			return 0;
+		}
+
+		return WEXITSTATUS(status);
+	}
+}
+
+#define run_test(name)			     \
+	if (name()) {			     \
+		tests_passed++;		     \
+	} else {			     \
+		tests_failed++;		     \
+		putstr("not ");		     \
+	}				     \
+	putstr("ok ");			     \
+	putnum(++tests_run);		     \
+	putstr(" " #name "\n");
+
+int main(int argc, char **argv)
+{
+	int ret, i;
+
+	putstr("TAP version 13\n");
+	putstr("1..");
+	putnum(EXPECTED_TESTS);
+	putstr("\n");
+
+	putstr("# PID: ");
+	putnum(getpid());
+	putstr("\n");
+
+	/*
+	 * This test is run with nolibc which doesn't support hwcap and
+	 * it's probably disproportionate to implement so instead check
+	 * for the default vector length configuration in /proc.
+	 */
+	ret = open("/proc/sys/abi/sme_default_vector_length", O_RDONLY, 0);
+	if (ret >= 0) {
+		run_test(default_value);
+		run_test(write_read);
+		run_test(write_sleep_read);
+		run_test(write_fork_read);
+		run_test(write_clone_read);
+
+	} else {
+		putstr("# SME support not present\n");
+
+		for (i = 0; i < EXPECTED_TESTS; i++) {
+			putstr("ok ");
+			putnum(i);
+			putstr(" skipped, TPIDR2 not supported\n");
+		}
+
+		tests_skipped += EXPECTED_TESTS;
+	}
+
+	print_summary();
+
+	return 0;
+}