[kvm-unit-tests PATCH v2 2/2] s390x: firq: floating interrupt test

David Hildenbrand
2021-12-02T12:36:12Z

We had a KVM BUG fixed by kernel commit a3e03bc1368c ("KVM: s390: index
kvm->arch.idle_mask by vcpu_idx"), whereby a floating interrupt might get
stuck forever because a CPU in the wait state would not get woken up.

The issue can be triggered when CPUs are created in a nonlinear fashion,
such that the CPU address ("core-id") and the KVM cpu id don't match.

So let's start with a floating interrupt test that will trigger a
floating interrupt (via SCLP) to be delivered to a CPU in the wait state.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
lib/s390x/sclp.c | 11 ++--
lib/s390x/sclp.h | 1 +
s390x/Makefile | 1 +
s390x/firq.c | 122 ++++++++++++++++++++++++++++++++++++++++++++
s390x/unittests.cfg | 10 ++++
5 files changed, 142 insertions(+), 3 deletions(-)
create mode 100644 s390x/firq.c

diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
index 0272249..33985eb 100644
--- a/lib/s390x/sclp.c
+++ b/lib/s390x/sclp.c
@@ -60,9 +60,7 @@ void sclp_setup_int(void)
void sclp_handle_ext(void)
{
ctl_clear_bit(0, CTL0_SERVICE_SIGNAL);
- spin_lock(&sclp_lock);
- sclp_busy = false;
- spin_unlock(&sclp_lock);
+ sclp_clear_busy();
}

void sclp_wait_busy(void)
@@ -89,6 +87,13 @@ void sclp_mark_busy(void)
}
}

+void sclp_clear_busy(void)
+{
+ spin_lock(&sclp_lock);
+ sclp_busy = false;
+ spin_unlock(&sclp_lock);
+}
+
static void sclp_read_scp_info(ReadInfo *ri, int length)
{
unsigned int commands[] = { SCLP_CMDW_READ_SCP_INFO_FORCED,
diff --git a/lib/s390x/sclp.h b/lib/s390x/sclp.h
index 61e9cf5..fead007 100644
--- a/lib/s390x/sclp.h
+++ b/lib/s390x/sclp.h
@@ -318,6 +318,7 @@ void sclp_setup_int(void);
void sclp_handle_ext(void);
void sclp_wait_busy(void);
void sclp_mark_busy(void);
+void sclp_clear_busy(void);
void sclp_console_setup(void);
void sclp_print(const char *str);
void sclp_read_info(void);
diff --git a/s390x/Makefile b/s390x/Makefile
index f95f2e6..1e567c1 100644
--- a/s390x/Makefile
+++ b/s390x/Makefile
@@ -25,6 +25,7 @@ tests += $(TEST_DIR)/uv-host.elf
tests += $(TEST_DIR)/edat.elf
tests += $(TEST_DIR)/mvpg-sie.elf
tests += $(TEST_DIR)/spec_ex-sie.elf
+tests += $(TEST_DIR)/firq.elf

tests_binary = $(patsubst %.elf,%.bin,$(tests))
ifneq ($(HOST_KEY_DOCUMENT),)
diff --git a/s390x/firq.c b/s390x/firq.c
new file mode 100644
index 0000000..1f87718
--- /dev/null
+++ b/s390x/firq.c
@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Floating interrupt tests.
+ *
+ * Copyright 2021 Red Hat Inc
+ *
+ * Authors:
+ * David Hildenbrand <david@redhat.com>
+ */
+#include <libcflat.h>
+#include <asm/asm-offsets.h>
+#include <asm/interrupt.h>
+#include <asm/page.h>
+#include <asm-generic/barrier.h>
+
+#include <sclp.h>
+#include <smp.h>
+#include <alloc_page.h>
+
+static void wait_for_sclp_int(void)
+{
+ /* Enable SCLP interrupts on this CPU only. */
+ ctl_set_bit(0, CTL0_SERVICE_SIGNAL);
+
+ /* Enable external interrupts and go to the wait state. */
+ wait_for_interrupt(PSW_MASK_EXT);
+}
+
+/*
+ * Some KVM versions might mix CPUs when looking for a floating IRQ target,
+ * accidentially detecting a stopped CPU as waiting and resulting in the actually
+ * waiting CPU not getting woken up for the interrupt.
+ */
+static void test_wait_state_delivery(void)
+{
+ struct psw psw;
+ SCCBHeader *h;
+ int ret;
+
+ report_prefix_push("wait state delivery");
+
+ if (smp_query_num_cpus() < 3) {
+ report_skip("need at least 3 CPUs for this test");
+ goto out;
+ }
+
+ if (stap()) {
+ report_skip("need to start on CPU #0");
+ goto out;
+ }
+
+ /*
+ * We want CPU #2 to be stopped. This should be the case at this
+ * point, however, we want to sense if it even exists as well.
+ */
+ ret = smp_cpu_stop(2);
+ if (ret) {
+ report_skip("CPU #2 not found");
+ goto out;
+ }
+
+ /*
+ * We're going to perform an SCLP service call but expect
+ * the interrupt on CPU #1 while it is in the wait state.
+ */
+ sclp_mark_busy();
+
+ /* Start CPU #1 and let it wait for the interrupt. */
+ psw.mask = extract_psw_mask();
+ psw.addr = (unsigned long)wait_for_sclp_int;
+ ret = smp_cpu_setup(1, psw);
+ if (ret) {
+ sclp_clear_busy();
+ report_skip("cpu #1 not found");
+ goto out;
+ }
+
+ /*
+ * We'd have to jump trough some hoops to sense e.g., via SIGP
+ * CONDITIONAL EMERGENCY SIGNAL if CPU #1 is already in the
+ * wait state.
+ *
+ * Although not completely reliable, use SIGP SENSE RUNNING STATUS
+ * until not reported as running -- after all, our SCLP processing
+ * will take some time as well and smp_cpu_setup() returns when we're
+ * either already in wait_for_sclp_int() or just about to execute it.
+ */
+ while(smp_sense_running_status(1));
+
+ h = alloc_page();
+ h->length = 4096;
+ ret = servc(SCLP_CMDW_READ_CPU_INFO, __pa(h));
+ if (ret) {
+ sclp_clear_busy();
+ report_fail("SCLP_CMDW_READ_CPU_INFO failed");
+ goto out_destroy;
+ }
+
+ /*
+ * Wait until the interrupt gets delivered on CPU #1, marking the
+ * SCLP requests as done.
+ */
+ sclp_wait_busy();
+
+ report(true, "sclp interrupt delivered");
+
+out_destroy:
+ free_page(h);
+ smp_cpu_destroy(1);
+out:
+ report_prefix_pop();
+}
+
+int main(void)
+{
+ report_prefix_push("firq");
+
+ test_wait_state_delivery();
+
+ report_prefix_pop();
+ return report_summary();
+}
diff --git a/s390x/unittests.cfg b/s390x/unittests.cfg
index 3b454b7..054560c 100644
--- a/s390x/unittests.cfg
+++ b/s390x/unittests.cfg
@@ -112,3 +112,13 @@ file = mvpg-sie.elf

[spec_ex-sie]
file = spec_ex-sie.elf
+
+[firq-linear-cpu-ids]
+file = firq.elf
+timeout = 20
+extra_params = -smp 1,maxcpus=3 -cpu qemu -device qemu-s390x-cpu,core-id=1 -device qemu-s390x-cpu,core-id=2
+
+[firq-nonlinear-cpu-ids]
+file = firq.elf
+timeout = 20
+extra_params = -smp 1,maxcpus=3 -cpu qemu -device qemu-s390x-cpu,core-id=2 -device qemu-s390x-cpu,core-id=1
--
2.31.1