[PATCH 2/4] hw/s390x/virtio-ccw: Always deliver NMI to first CPU

[Philippe Mathieu-Daudé]

We can trigger NMI from HMP or QMP.

QEMU maps the NMI to the s390x per-CPU 'RESTART' interrupt.
Linux guests usually setup this interrupt to trigger kdump
or crash. Such crashdump can be triggered in QEMU by HMP
"nmi" or QMP "inject-nmi" commands.

Using QMP, since we can not select a particular CPU, the first
CPU is used (CPU#0). See the documentation from commit 795dc6e4
("watchdog: Add new Virtual Watchdog action INJECT-NMI"):

  @inject-nmi: a non-maskable interrupt is injected into the
               first VCPU (all VCPUS on x86) (since 2.4)

While we can select a particular CPU on HMP, the guest behavior
is expected to be the same if using CPU #N or CPU #0. Since
always using CPU#0 simplifies API maintainance, update s390_nmi()
to deliver NMI to the first CPU.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 qapi/run-state.json        | 5 +++--
 hw/s390x/s390-virtio-ccw.c | 4 +---
 hmp-commands.hx            | 2 +-
 3 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/qapi/run-state.json b/qapi/run-state.json
index 08bc99cb85..a2542f1a50 100644
--- a/qapi/run-state.json
+++ b/qapi/run-state.json
@@ -320,8 +320,9 @@
 #
 # @none: nothing is done
 #
-# @inject-nmi: a non-maskable interrupt is injected into the first
-#     VCPU (all VCPUS on x86) (since 2.4)
+# @inject-nmi: a non-maskable interrupt is injected (architecture
+#     specific: on s390x only the first vCPU receive the NMI, on
+#     other architectures all vCPUs receive it). (since 2.4)
 #
 # Since: 2.1
 ##
diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 62804cc228..ba1fa6472f 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -605,9 +605,7 @@ static HotplugHandler 
*s390_get_hotplug_handler(MachineState *machine,
 
 static void s390_nmi(NMIState *n, int cpu_index, Error **errp)
 {
-    CPUState *cs = qemu_get_cpu(cpu_index);
-
-    s390_cpu_restart(S390_CPU(cs));
+    s390_cpu_restart(S390_CPU(first_cpu));
 }
 
 static ram_addr_t s390_fixup_ram_size(ram_addr_t sz)
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 17b5ea839d..2b01bb5926 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -851,7 +851,7 @@ ERST
     },
 SRST
 ``nmi`` *cpu*
-  Inject an NMI on the default CPU (x86/s390) or all CPUs (ppc64).
+  Inject an NMI.
 ERST
 
     {
-- 
2.41.0