[kvm-unit-tests PATCH v5 3/4] 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>
Reviewed-by: Thomas Huth <thuth@redhat.com>
---
 s390x/Makefile            |  1 +
 s390x/panic-loop-extint.c | 59 +++++++++++++++++++++++++++++++++++++++
 s390x/unittests.cfg       |  6 ++++
 3 files changed, 66 insertions(+)
 create mode 100644 s390x/panic-loop-extint.c

diff --git a/s390x/Makefile b/s390x/Makefile
index efd5e0c13102..e4649da50d9d 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)/panic-loop-extint.elf
 
 pv-tests += $(TEST_DIR)/pv-diags.elf
 
diff --git a/s390x/panic-loop-extint.c b/s390x/panic-loop-extint.c
new file mode 100644
index 000000000000..07325147dc17
--- /dev/null
+++ b/s390x/panic-loop-extint.c
@@ -0,0 +1,59 @@
+/* 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>
+#include <hardware.h>
+#include <bitops.h>
+
+static void ext_int_cleanup(struct stack_frame_int *stack)
+{
+	/*
+	 * Since we form a loop of ext interrupts, this code should never be
+	 * executed. In case it is executed, something went wrong and we want to
+	 * print a failure.
+	 *
+	 * Because the CPU timer subclass mask is still enabled, the CPU timer
+	 * interrupt will fire every time we enable external interrupts,
+	 * preventing us from printing the failure on the console. To avoid
+	 * this, clear the CPU timer subclass mask here.
+	 */
+	stack->crs[0] &= ~BIT(CTL0_CPU_TIMER);
+}
+
+int main(void)
+{
+	report_prefix_push("panic-loop-extint");
+
+	if (!host_is_qemu() || host_is_tcg()) {
+		report_skip("QEMU-KVM-only test");
+		goto out;
+	}
+
+	expect_ext_int();
+	lowcore.ext_new_psw.mask |= PSW_MASK_EXT;
+
+	psw_mask_set_bits(PSW_MASK_EXT);
+
+	register_ext_cleanup_func(ext_int_cleanup);
+
+	cpu_timer_set_ms(10);
+	ctl_set_bit(0, CTL0_CPU_TIMER);
+	mdelay(2000);
+
+	register_ext_cleanup_func(NULL);
+
+	report_fail("survived extint loop");
+
+out:
+	report_prefix_pop();
+	return report_summary();
+}
diff --git a/s390x/unittests.cfg b/s390x/unittests.cfg
index f7b1fc3dbca1..b1b25f118ff6 100644
--- a/s390x/unittests.cfg
+++ b/s390x/unittests.cfg
@@ -185,3 +185,9 @@ groups = migration
 [migration-skey]
 file = migration-skey.elf
 groups = migration
+
+[panic-loop-extint]
+file = panic-loop-extint.elf
+groups = panic
+accel = kvm
+timeout = 5
-- 
2.36.1