kselftest/arm64: tpidr2: Adjust to new clone() behaviour

In order to fix an ABI problem, we recently changed the way that a
clone() syscall manipulates TPIDR2 and PSTATE.ZA. Historically the child
would inherit the parent's TPIDR2 value unless CLONE_SETTLS was set, and
now the child will inherit the parent's TPIDR2 value unless CLONE_VM is
set.

Update the tpidr2 test for the new behaviour.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Daniel Kiss <daniel.kiss@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Richard Sandiford <richard.sandiford@arm.com>
Cc: Sander De Smalen <sander.desmalen@arm.com>
Cc: Tamas Petz <tamas.petz@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yury Khrustalev <yury.khrustalev@arm.com>
Link: https://lore.kernel.org/r/20250508132644.1395904-23-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: mrutland-arm

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

@@ -169,8 +169,10 @@ static int sys_clone(unsigned long clone_flags, unsigned long newsp,
 			   child_tidptr);
 }
 
+#define __STACK_SIZE (8 * 1024 * 1024)
+
 /*
- * If we clone with CLONE_SETTLS then the value in the parent should
+ * If we clone with CLONE_VM then the value in the parent should
  * be unchanged and the child should start with zero and be able to
  * set its own value.
  */
@@ -179,11 +181,19 @@ static int write_clone_read(void)
 	int parent_tid, child_tid;
 	pid_t parent, waiting;
 	int ret, status;
+	void *stack;
 
 	parent = getpid();
 	set_tpidr2(parent);
 
-	ret = sys_clone(CLONE_SETTLS, 0, &parent_tid, 0, &child_tid);
+	stack = malloc(__STACK_SIZE);
+	if (!stack) {
+		putstr("# malloc() failed\n");
+		return 0;
+	}
+
+	ret = sys_clone(CLONE_VM, (unsigned long)stack + __STACK_SIZE,
+			&parent_tid, 0, &child_tid);
 	if (ret == -1) {
 		putstr("# clone() failed\n");
 		putnum(errno);