[PATCH v4 2/7] hw/s390x/virtio-ccw: Always inject NMI to first CPU

["Philippe Mathieu-Daudé" <philmd@oss.qualcomm.com>]

From: Philippe Mathieu-Daudé <philmd@linaro.org>

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 inject NMI to the first CPU.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
---
 qapi/machine.json          | 7 ++++---
 qapi/run-state.json        | 6 ++++--
 hw/s390x/s390-virtio-ccw.c | 4 +---
 hmp-commands.hx            | 5 +++--
 4 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/qapi/machine.json b/qapi/machine.json
index 9b2248038fc..2d63c1bac3b 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -432,9 +432,10 @@
 ##
 # @inject-nmi:
 #
-# Injects a Non-Maskable Interrupt into the default CPU (x86/s390) or
-# all CPUs (ppc64).  The command fails when the guest doesn't support
-# injecting.
+# Injects a Non-Maskable Interrupt (machine specific: for example on
+# s390x CCW only the first vCPU receives the NMI, but on x86 machines
+# all vCPUs receive it).  The command fails when the guest doesn't
+# support injecting.
 #
 # Since: 0.14
 #
diff --git a/qapi/run-state.json b/qapi/run-state.json
index a5771ad4681..e4fdead1e0b 100644
--- a/qapi/run-state.json
+++ b/qapi/run-state.json
@@ -317,8 +317,10 @@
 #
 # @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 (machine
+#     specific: for example on s390x CCW only the first vCPU
+#     receives the NMI, but on x86 machines 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 25a9fa49554..4f7861dbbb7 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -727,9 +727,7 @@ 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 inline bool machine_get_aes_key_wrap(Object *obj, Error **errp)
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 7ae2468a3d9..a1b77ae4044 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -865,12 +865,13 @@ ERST
         .name       = "nmi",
         .args_type  = "",
         .params     = "",
-        .help       = "inject an NMI",
+        .help       = "Inject an NMI, in a machine-specific way",
         .cmd        = hmp_nmi,
     },
 SRST
 ``nmi`` *cpu*
-  Inject an NMI on the default CPU (x86/s390) or all CPUs (ppc64).
+  Inject an NMI, in a machine-specific way.
+  Not all machines implement NMI handling.
 ERST
 
     {
-- 
2.53.0