[kvm-unit-tests PATCH v1 2/3] s390x: add extint loop test

[Nico Boehr <nrb@linux.ibm.com>]

The CPU timer interrupt stays pending as long as the CPU timer value is
negative. This can lead to interruption loops when the ext_new_psw mask
has external interrupts enabled.

QEMU is able to detect this situation and panic the guest, so add a test
for it.

Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
---
 s390x/Makefile      |  1 +
 s390x/extint-loop.c | 64 +++++++++++++++++++++++++++++++++++++++++++++
 s390x/unittests.cfg |  4 +++
 3 files changed, 69 insertions(+)
 create mode 100644 s390x/extint-loop.c

diff --git a/s390x/Makefile b/s390x/Makefile
index efd5e0c13102..92a020234c9f 100644
--- a/s390x/Makefile
+++ b/s390x/Makefile
@@ -34,6 +34,7 @@ tests += $(TEST_DIR)/migration.elf
 tests += $(TEST_DIR)/pv-attest.elf
 tests += $(TEST_DIR)/migration-cmm.elf
 tests += $(TEST_DIR)/migration-skey.elf
+tests += $(TEST_DIR)/extint-loop.elf
 
 pv-tests += $(TEST_DIR)/pv-diags.elf
 
diff --git a/s390x/extint-loop.c b/s390x/extint-loop.c
new file mode 100644
index 000000000000..5276d86a156f
--- /dev/null
+++ b/s390x/extint-loop.c
@@ -0,0 +1,64 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * External interrupt loop test
+ *
+ * Copyright IBM Corp. 2022
+ *
+ * Authors:
+ *  Nico Boehr <nrb@linux.ibm.com>
+ */
+#include <libcflat.h>
+#include <asm/interrupt.h>
+#include <asm/barrier.h>
+#include <asm/time.h>
+
+static void ext_int_handler(void)
+{
+	/*
+	 * return to ext_old_psw. This gives us the chance to print the return_fail
+	 * in case something goes wrong.
+	 */
+	asm volatile (
+		"lpswe %[ext_old_psw]\n"
+		:
+		: [ext_old_psw] "Q"(lowcore.ext_old_psw)
+		: "memory"
+	);
+}
+
+static void start_cpu_timer(int64_t timeout_ms)
+{
+#define CPU_TIMER_US_SHIFT 12
+	int64_t timer_value = (timeout_ms * 1000) << CPU_TIMER_US_SHIFT;
+	asm volatile (
+		"spt %[timer_value]\n"
+		:
+		: [timer_value] "Q" (timer_value)
+	);
+}
+
+int main(void)
+{
+	struct psw ext_new_psw_orig;
+
+	report_prefix_push("extint-loop");
+
+	ext_new_psw_orig = lowcore.ext_new_psw;
+	lowcore.ext_new_psw.addr = (uint64_t)ext_int_handler;
+	lowcore.ext_new_psw.mask |= PSW_MASK_EXT;
+
+	load_psw_mask(extract_psw_mask() | PSW_MASK_EXT);
+	ctl_set_bit(0, CTL0_CLOCK_COMPARATOR);
+
+	start_cpu_timer(1);
+
+	mdelay(2000);
+
+	/* restore previous ext_new_psw so QEMU can properly terminate */
+	lowcore.ext_new_psw = ext_new_psw_orig;
+
+	report_fail("survived extint loop");
+
+	report_prefix_pop();
+	return report_summary();
+}
diff --git a/s390x/unittests.cfg b/s390x/unittests.cfg
index 8e52f560bb1e..7d408f2d5310 100644
--- a/s390x/unittests.cfg
+++ b/s390x/unittests.cfg
@@ -184,3 +184,7 @@ groups = migration
 [migration-skey]
 file = migration-skey.elf
 groups = migration
+
+[extint-loop]
+file = extint-loop.elf
+groups = panic
-- 
2.36.1