tests/arm_interrupt: Disable persistent lock test when USE_SWITCH=y

I'm at a loss here.  The feature this test case wants to see (on
ARMv7M, not ARMv6M) is the ability to take a irq_lock() inside a
system call and then see that future system calls from the same thread
continue to hold the lock.

That's not documented AFAICT.  It's also just a terrible idea because
either:

1. The obvious denial of service implications if user code is allowed
   to run in an unpreemptible mode, or:

2. The broken locking promise if this is implemented to release the
   lock and reacquire it in an attempt to avoid #1.

(FWIW: my read of the code is that #1 is the current implementation.
But hilariously the test isn't able to tell the difference!)

And in any case it's not how any of our other platforms work (or can
work, in some cases), making this a non-portable system call
API/feature at best.

Leave it in place for now out of conservatism, but disable with the
new arch_switch() code, whose behavior matches that of other Zephyr
userspaces.

Signed-off-by: Andy Ross <[email protected]>

Author: andyross

tests/arch/arm/arm_interrupt/src/arm_interrupt.c

@@ -371,8 +371,19 @@ void z_impl_test_arm_user_interrupt_syscall(void)
 #if defined(CONFIG_ARMV6_M_ARMV8_M_BASELINE)
 	/* Confirm IRQs are not locked */
 	zassert_false(__get_PRIMASK(), "PRIMASK is set\n");
-#elif defined(CONFIG_ARMV7_M_ARMV8_M_MAINLINE)
-
+#elif defined(CONFIG_ARMV7_M_ARMV8_M_MAINLINE) && defined(CONFIG_USE_SWITCH)
+	/* Confirm IRQs are not locked */
+	zassert_false(__get_BASEPRI(), "BASEPRI is set\n");
+#elif defined(CONFIG_ARMV7_M_ARMV8_M_MAINLINE) && !defined(CONFIG_USE_SWITCH)
+	/* The original ARMv7M userspace implementation had the
+	 * somewhat odd (and dangerous!) behavior that an interrupt
+	 * mask done in a system call would persist (!!) on return
+	 * into userspace, and be seen again once we were back in
+	 * kernel mode, and this is a test for it.  It's legacy
+	 * though, not something we ever documented, and not the way
+	 * userspace works (or even can work!) on other platforms, nor
+	 * with the newer arch_switch() code.  Consider removing.
+	 */
 	static bool first_call = 1;
 
 	if (first_call == 1) {