vl: Add option to avoid stopping VM upon guest panic

The current default action of pausing a guest after a panic event
is received leaves the responsibility to resume guest execution to the
management layer. The reasons for this behavior are discussed here:
https://lore.kernel.org/qemu-devel/52148F88.5000509@redhat.com/

However, in instances like the case of older guests (Linux and
Windows) using a pvpanic device but missing support for the
PVPANIC_CRASHLOADED event, and Windows guests using the hv-crash
enlightenment, it is desirable to allow the guests to continue
running after sending a PVPANIC_PANICKED event. This allows such
guests to proceed to capture a crash dump and automatically reboot
without intervention of a management layer.

Add an option to avoid stopping a VM after a panic event is received,
by passing:

-action panic=none

in the command line arguments, or during runtime by using an upcoming
QMP command.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Message-Id: <1607705564-26264-3-git-send-email-alejandro.j.jimenez@oracle.com>
[Do not fix panic action in the variable, instead modify -no-shutdown. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 23 insertions, 5 deletions

diff --git a/softmmu/runstate-action.c b/softmmu/runstate-action.c
index 44de01adaf..99ce880886 100644
--- a/softmmu/runstate-action.c
+++ b/softmmu/runstate-action.c
@@ -15,6 +15,7 @@
 
 RebootAction reboot_action = REBOOT_ACTION_NONE;
 ShutdownAction shutdown_action = SHUTDOWN_ACTION_POWEROFF;
+PanicAction panic_action = PANIC_ACTION_POWEROFF;
 
 /*
  * Receives actions to be applied for specific guest events
@@ -30,6 +31,10 @@ void qmp_set_action(bool has_reboot, RebootAction reboot,
         reboot_action = reboot;
     }
 
+    if (has_panic) {
+        panic_action = panic;
+    }
+
     if (has_watchdog) {
         qmp_watchdog_set_action(watchdog, errp);
     }
diff --git a/softmmu/runstate.c b/softmmu/runstate.c
index bd0522ed9e..636aab0add 100644
--- a/softmmu/runstate.c
+++ b/softmmu/runstate.c
@@ -469,13 +469,23 @@ void qemu_system_guest_panicked(GuestPanicInformation *info)
     if (current_cpu) {
         current_cpu->crash_occurred = true;
     }
-    qapi_event_send_guest_panicked(GUEST_PANIC_ACTION_PAUSE,
-                                   !!info, info);
-    vm_stop(RUN_STATE_GUEST_PANICKED);
-    if (shutdown_action == SHUTDOWN_ACTION_POWEROFF) {
+    /*
+     * TODO:  Currently the available panic actions are: none, pause, and
+     * poweroff, but in principle debug and reset could be supported as well.
+     * Investigate any potential use cases for the unimplemented actions.
+     */
+    if (panic_action == PANIC_ACTION_PAUSE) {
+        qapi_event_send_guest_panicked(GUEST_PANIC_ACTION_PAUSE,
+                                        !!info, info);
+        vm_stop(RUN_STATE_GUEST_PANICKED);
+    } else if (panic_action == PANIC_ACTION_POWEROFF) {
         qapi_event_send_guest_panicked(GUEST_PANIC_ACTION_POWEROFF,
                                        !!info, info);
+        vm_stop(RUN_STATE_GUEST_PANICKED);
         qemu_system_shutdown_request(SHUTDOWN_CAUSE_GUEST_PANIC);
+    } else {
+        qapi_event_send_guest_panicked(GUEST_PANIC_ACTION_RUN,
+                                        !!info, info);
     }
 
     if (info) {
diff --git a/softmmu/vl.c b/softmmu/vl.c
index 6d1a7ebb08..3921a04f77 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -490,6 +490,9 @@ static QemuOptsList qemu_action_opts = {
             .name = "reboot",
             .type = QEMU_OPT_STRING,
         },{
+            .name = "panic",
+            .type = QEMU_OPT_STRING,
+        },{
             .name = "watchdog",
             .type = QEMU_OPT_STRING,
         },
@@ -3212,7 +3215,7 @@ void qemu_init(int argc, char **argv, char **envp)
                 break;
             case QEMU_OPTION_no_shutdown:
                 olist = qemu_find_opts("action");
-                qemu_opts_parse_noisily(olist, "shutdown=pause", false);
+                qemu_opts_parse_noisily(olist, "panic=pause,shutdown=pause", false);
                 break;
             case QEMU_OPTION_show_cursor:
                 warn_report("The -show-cursor option is deprecated. Please "