kselftest/arm64: Add a test case for SVE VL changes with SME active

We just fixed an issue where changing the SVE VL while SME was active could
result in us attempting to save the streaming mode SVE vectors without any
backing storage. Add a test case which provokes that issue, ideally we
should also verify that the contents of ZA are unaffected by any of what we
did.

Note that since we need to keep streaming mode enabled we can't use any
syscalls to trigger the issue, we have to sit in a loop in usersapce and
hope to be preempted. The chosen numbers trigger with defconfig on all the
virtual platforms for me, this won't be 100% on all systems but avoid an
overcomplicated test implementation.

Signed-off-by: Mark Brown <[email protected]>
Link: https://lore.kernel.org/r/20230720-arm64-fix-sve-sme-vl-change-v2-2-8eea06b82d57@kernel.org
Signed-off-by: Will Deacon <[email protected]>

Author: broonie

tools/testing/selftests/arm64/fp/vec-syscfg.c

@@ -6,6 +6,7 @@
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -39,9 +40,11 @@ struct vec_data {
 	int max_vl;
 };
 
+#define VEC_SVE 0
+#define VEC_SME 1
 
 static struct vec_data vec_data[] = {
-	{
+	[VEC_SVE] = {
 		.name = "SVE",
 		.hwcap_type = AT_HWCAP,
 		.hwcap = HWCAP_SVE,
@@ -51,7 +54,7 @@ static struct vec_data vec_data[] = {
 		.prctl_set = PR_SVE_SET_VL,
 		.default_vl_file = "/proc/sys/abi/sve_default_vector_length",
 	},
-	{
+	[VEC_SME] = {
 		.name = "SME",
 		.hwcap_type = AT_HWCAP2,
 		.hwcap = HWCAP2_SME,
@@ -644,18 +647,107 @@ static const test_type tests[] = {
 	prctl_set_all_vqs,
 };
 
+static inline void smstart(void)
+{
+	asm volatile("msr S0_3_C4_C7_3, xzr");
+}
+
+static inline void smstart_sm(void)
+{
+	asm volatile("msr S0_3_C4_C3_3, xzr");
+}
+
+static inline void smstop(void)
+{
+	asm volatile("msr S0_3_C4_C6_3, xzr");
+}
+
+
+/*
+ * Verify we can change the SVE vector length while SME is active and
+ * continue to use SME afterwards.
+ */
+static void change_sve_with_za(void)
+{
+	struct vec_data *sve_data = &vec_data[VEC_SVE];
+	bool pass = true;
+	int ret, i;
+
+	if (sve_data->min_vl == sve_data->max_vl) {
+		ksft_print_msg("Only one SVE VL supported, can't change\n");
+		ksft_test_result_skip("change_sve_while_sme\n");
+		return;
+	}
+
+	/* Ensure we will trigger a change when we set the maximum */
+	ret = prctl(sve_data->prctl_set, sve_data->min_vl);
+	if (ret != sve_data->min_vl) {
+		ksft_print_msg("Failed to set SVE VL %d: %d\n",
+			       sve_data->min_vl, ret);
+		pass = false;
+	}
+
+	/* Enable SM and ZA */
+	smstart();
+
+	/* Trigger another VL change */
+	ret = prctl(sve_data->prctl_set, sve_data->max_vl);
+	if (ret != sve_data->max_vl) {
+		ksft_print_msg("Failed to set SVE VL %d: %d\n",
+			       sve_data->max_vl, ret);
+		pass = false;
+	}
+
+	/*
+	 * Spin for a bit with SM enabled to try to trigger another
+	 * save/restore.  We can't use syscalls without exiting
+	 * streaming mode.
+	 */
+	for (i = 0; i < 100000000; i++)
+		smstart_sm();
+
+	/*
+	 * TODO: Verify that ZA was preserved over the VL change and
+	 * spin.
+	 */
+
+	/* Clean up after ourselves */
+	smstop();
+	ret = prctl(sve_data->prctl_set, sve_data->default_vl);
+	if (ret != sve_data->default_vl) {
+	        ksft_print_msg("Failed to restore SVE VL %d: %d\n",
+			       sve_data->default_vl, ret);
+		pass = false;
+	}
+
+	ksft_test_result(pass, "change_sve_with_za\n");
+}
+
+typedef void (*test_all_type)(void);
+
+static const struct {
+	const char *name;
+	test_all_type test;
+}  all_types_tests[] = {
+	{ "change_sve_with_za", change_sve_with_za },
+};
+
 int main(void)
 {
+	bool all_supported = true;
 	int i, j;
 
 	ksft_print_header();
-	ksft_set_plan(ARRAY_SIZE(tests) * ARRAY_SIZE(vec_data));
+	ksft_set_plan(ARRAY_SIZE(tests) * ARRAY_SIZE(vec_data) +
+		      ARRAY_SIZE(all_types_tests));
 
 	for (i = 0; i < ARRAY_SIZE(vec_data); i++) {
 		struct vec_data *data = &vec_data[i];
 		unsigned long supported;
 
 		supported = getauxval(data->hwcap_type) & data->hwcap;
+		if (!supported)
+			all_supported = false;
 
 		for (j = 0; j < ARRAY_SIZE(tests); j++) {
 			if (supported)
@@ -666,5 +758,12 @@ int main(void)
 		}
 	}
 
+	for (i = 0; i < ARRAY_SIZE(all_types_tests); i++) {
+		if (all_supported)
+			all_types_tests[i].test();
+		else
+			ksft_test_result_skip("%s\n", all_types_tests[i].name);
+	}
+
 	ksft_exit_pass();
 }