selftests: arm64: Add coverage of ptrace flags for SVE VL inheritance

Add a test that covers enabling and disabling of SVE vector length
inheritance via the ptrace interface.

Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20211005123537.976795-1-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

tools/testing/selftests/arm64/fp/sve-ptrace.c

@@ -22,7 +22,7 @@
 #include "../../kselftest.h"
 
 #define VL_TESTS (((SVE_VQ_MAX - SVE_VQ_MIN) + 1) * 3)
-#define FPSIMD_TESTS 3
+#define FPSIMD_TESTS 5
 
 #define EXPECTED_TESTS (VL_TESTS + FPSIMD_TESTS)
 
@@ -105,6 +105,56 @@ static int set_sve(pid_t pid, const struct user_sve_header *sve)
 	return ptrace(PTRACE_SETREGSET, pid, NT_ARM_SVE, &iov);
 }
 
+/* Validate setting and getting the inherit flag */
+static void ptrace_set_get_inherit(pid_t child)
+{
+	struct user_sve_header sve;
+	struct user_sve_header *new_sve = NULL;
+	size_t new_sve_size = 0;
+	int ret;
+
+	/* First set the flag */
+	memset(&sve, 0, sizeof(sve));
+	sve.size = sizeof(sve);
+	sve.vl = sve_vl_from_vq(SVE_VQ_MIN);
+	sve.flags = SVE_PT_VL_INHERIT;
+	ret = set_sve(child, &sve);
+	if (ret != 0) {
+		ksft_test_result_fail("Failed to set SVE_PT_VL_INHERIT\n");
+		return;
+	}
+
+	/*
+	 * Read back the new register state and verify that we have
+	 * set the flags we expected.
+	 */
+	if (!get_sve(child, (void **)&new_sve, &new_sve_size)) {
+		ksft_test_result_fail("Failed to read SVE flags\n");
+		return;
+	}
+
+	ksft_test_result(new_sve->flags & SVE_PT_VL_INHERIT,
+			 "SVE_PT_VL_INHERIT set\n");
+
+	/* Now clear */
+	sve.flags &= ~SVE_PT_VL_INHERIT;
+	ret = set_sve(child, &sve);
+	if (ret != 0) {
+		ksft_test_result_fail("Failed to clear SVE_PT_VL_INHERIT\n");
+		return;
+	}
+
+	if (!get_sve(child, (void **)&new_sve, &new_sve_size)) {
+		ksft_test_result_fail("Failed to read SVE flags\n");
+		return;
+	}
+
+	ksft_test_result(!(new_sve->flags & SVE_PT_VL_INHERIT),
+			 "SVE_PT_VL_INHERIT cleared\n");
+
+	free(new_sve);
+}
+
 /* Validate attempting to set the specfied VL via ptrace */
 static void ptrace_set_get_vl(pid_t child, unsigned int vl, bool *supported)
 {
@@ -452,6 +502,9 @@ static int do_parent(pid_t child)
 	/* FPSIMD via SVE regset */
 	ptrace_sve_fpsimd(child);
 
+	/* prctl() flags */
+	ptrace_set_get_inherit(child);
+
 	/* Step through every possible VQ */
 	for (vq = SVE_VQ_MIN; vq <= SVE_VQ_MAX; vq++) {
 		vl = sve_vl_from_vq(vq);