Use first_cpu directly instead of going through monitor_get_cpu_index(),
as this is HMP-territory. QMP doesn't have a `cpu` command, we should
add arguments instead when needed.

Update the inject-nmi doc to accurately describe per-architecture NMI
delivery.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 qapi/machine.json | 5 +++--
 system/cpus.c     | 7 +++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/qapi/machine.json b/qapi/machine.json
index 685e4e29b87..03461f5f723 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -432,8 +432,9 @@
 ##
 # @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
+# Injects a Non-Maskable Interrupt into the virtual machine.  The NMI
+# is delivered to all vCPUs (x86, hppa, ppc64) or to the first vCPU
+# (s390).  The command fails when the guest doesn't support
 # injecting.
 #
 # Since: 0.14
diff --git a/system/cpus.c b/system/cpus.c
index bded87feb1c..0089eef9b1c 100644
--- a/system/cpus.c
+++ b/system/cpus.c
@@ -913,6 +913,9 @@ exit:
 
 void qmp_inject_nmi(Error **errp)
 {
-    nmi_monitor_handle(monitor_get_cpu_index(monitor_cur()), errp);
+    int cpu_index = UNASSIGNED_CPU_INDEX;
+    if (first_cpu) {
+        cpu_index = first_cpu->cpu_index;
+    }
+    nmi_monitor_handle(cpu_index, errp);
 }
-

-- 
2.54.0