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>

6 files changed, 43 insertions, 5 deletions

diff --git a/include/sysemu/runstate-action.h b/include/sysemu/runstate-action.h
index 51a461c4ac..cff45a047b 100644
--- a/include/sysemu/runstate-action.h
+++ b/include/sysemu/runstate-action.h
@@ -14,5 +14,6 @@
 /* in softmmu/runstate-action.c */
 extern RebootAction reboot_action;
 extern ShutdownAction shutdown_action;
+extern PanicAction panic_action;
 
 #endif /* RUNSTATE_ACTION_H */
diff --git a/qapi/run-state.json b/qapi/run-state.json
index 25e82d1be1..1f3b329f05 100644
--- a/qapi/run-state.json
+++ b/qapi/run-state.json
@@ -354,6 +354,18 @@
   'data': [ 'poweroff', 'pause' ] }
 
 ##
+# @PanicAction:
+#
+# @none: Continue VM execution
+#
+# @pause: Pause the VM
+#
+# Since: 6.0
+##
+{ 'enum': 'PanicAction',
+  'data': [ 'poweroff', 'pause', 'none' ] }
+
+##
 # @watchdog-set-action:
 #
 # Set watchdog action
@@ -372,6 +384,8 @@
 #
 # @shutdown: @ShutdownAction action taken on guest shutdown.
 #
+# @panic: @PanicAction action taken on guest panic.
+#
 # @watchdog: @WatchdogAction action taken when watchdog timer expires .
 #
 # Returns: Nothing on success.
@@ -383,12 +397,14 @@
 # -> { "execute": "set-action",
 #      "arguments": { "reboot": "shutdown",
 #                     "shutdown" : "pause",
+#                     "panic": "pause",
 #                     "watchdog": "inject-nmi" } }
 # <- { "return": {} }
 ##
 { 'command': 'set-action',
   'data': { '*reboot': 'RebootAction',
             '*shutdown': 'ShutdownAction',
+            '*panic': 'PanicAction',
             '*watchdog': 'WatchdogAction' },
   'allow-preconfig': true }
 
diff --git a/qemu-options.hx b/qemu-options.hx
index eb55cd0eea..94cdfcf32e 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3899,6 +3899,8 @@ DEF("action", HAS_ARG, QEMU_OPTION_action,
     "                   action when guest reboots [default=none]\n"
     "-action shutdown=poweroff|pause\n"
     "                   action when guest shuts down [default=poweroff]\n"
+    "-action panic=poweroff|pause|none\n"
+    "                   action when guest panics [default=poweroff]\n"
     "-action watchdog=reset|shutdown|poweroff|inject-nmi|pause|debug|none\n"
     "                   action when watchdog fires [default=reset]\n",
     QEMU_ARCH_ALL)
@@ -3911,6 +3913,7 @@ SRST
 
     Examples:
 
+    ``-action panic=none``
     ``-action reboot=shutdown,shutdown=pause``
     ``-watchdog i6300esb -action watchdog=pause``
 
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 "