[PATCH] xen: add support for automatic debug key actions in case of crash

[Juergen Gross <jgross@xxxxxxxx>]

When the host crashes it would sometimes be nice to have additional
debug data available which could be produced via debug keys, but
halting the server for manual intervention might be impossible due to
the need to reboot/kexec rather sooner than later.

Add support for automatic debug key actions in case of crashes which
can be activated via boot- or runtime-parameter.

Depending on the type of crash the desired data might be different, so
support different settings for the possible types of crashes.

The parameter is "crash-debug" with the following syntax:

  crash-debug-<type>=<string>

with <type> being one of:

  panic, hwdom, watchdog, kexeccmd, debugkey

and <string> a sequence of debug key characters with '.' having the
special semantics of a 1 second pause.

So "crash-debug-watchdog=0.0qr" would result in special output in case
of watchdog triggered crash (dom0 state, 1 second pause, dom0 state,
domain info, run queues).

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 docs/misc/xen-command-line.pandoc | 23 +++++++++++++++++++
 xen/common/kexec.c                |  8 ++++---
 xen/common/keyhandler.c           | 37 +++++++++++++++++++++++++++++++
 xen/common/shutdown.c             |  4 ++--
 xen/drivers/char/console.c        |  2 +-
 xen/include/xen/kexec.h           | 10 +++++++--
 xen/include/xen/keyhandler.h      | 11 +++++++++
 7 files changed, 87 insertions(+), 8 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index 4ae9391fcd..f328c99cf8 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -574,6 +574,29 @@ reduction of features at Xen's disposal to manage guests.
 ### cpuinfo (x86)
 > `= <boolean>`
 
+### crash-debug-debugkey
+### crash-debug-hwdom
+### crash-debug-kexeccmd
+### crash-debug-panic
+### crash-debug-watchdog
+> `= <string>`
+
+> Can be modified at runtime
+
+Specify debug-key actions in cases of crashes. Each of the parameters applies
+to a different crash reason. The `<string>` is a sequence of debug key
+characters, with `.` having the special meaning of a 1 second pause.
+
+So e.g. `crash-debug-watchdog=0.0r` would dump dom0 state twice with a
+second between the two state dumps, followed by the run queues of the
+hypervisor, if the system crashes due to a watchdog timeout.
+
+These parameters should be used carefully, as e.g. specifying
+`crash-debug-debugkey=C` would result in an endless loop. Depending on the
+reason of the system crash it might happen that triggering some debug key
+action will result in a hang instead of dumping data and then doing a
+reboot or crash dump.
+
 ### crashinfo_maxaddr
 > `= <size>`
 
diff --git a/xen/common/kexec.c b/xen/common/kexec.c
index 52cdc4ebc3..ebeee6405a 100644
--- a/xen/common/kexec.c
+++ b/xen/common/kexec.c
@@ -373,10 +373,12 @@ static int kexec_common_shutdown(void)
     return 0;
 }
 
-void kexec_crash(void)
+void kexec_crash(enum crash_reason reason)
 {
     int pos;
 
+    keyhandler_crash_action(reason);
+
     pos = (test_bit(KEXEC_FLAG_CRASH_POS, &kexec_flags) != 0);
     if ( !test_bit(KEXEC_IMAGE_CRASH_BASE + pos, &kexec_flags) )
         return;
@@ -409,7 +411,7 @@ static long kexec_reboot(void *_image)
 static void do_crashdump_trigger(unsigned char key)
 {
     printk("'%c' pressed -> triggering crashdump\n", key);
-    kexec_crash();
+    kexec_crash(CRASHREASON_DEBUGKEY);
     printk(" * no crash kernel loaded!\n");
 }
 
@@ -840,7 +842,7 @@ static int kexec_exec(XEN_GUEST_HANDLE_PARAM(void) uarg)
         ret = continue_hypercall_on_cpu(0, kexec_reboot, image);
         break;
     case KEXEC_TYPE_CRASH:
-        kexec_crash(); /* Does not return */
+        kexec_crash(CRASHREASON_KEXECCMD); /* Does not return */
         break;
     }
 
diff --git a/xen/common/keyhandler.c b/xen/common/keyhandler.c
index 68364e987d..ac8229a4d7 100644
--- a/xen/common/keyhandler.c
+++ b/xen/common/keyhandler.c
@@ -3,7 +3,9 @@
  */
 
 #include <asm/regs.h>
+#include <xen/delay.h>
 #include <xen/keyhandler.h>
+#include <xen/param.h>
 #include <xen/shutdown.h>
 #include <xen/event.h>
 #include <xen/console.h>
@@ -507,6 +509,41 @@ void __init initialize_keytable(void)
     }
 }
 
+#define CRASHACTION_SIZE  32
+static char crash_debug_panic[CRASHACTION_SIZE];
+static char crash_debug_hwdom[CRASHACTION_SIZE];
+static char crash_debug_watchdog[CRASHACTION_SIZE];
+static char crash_debug_kexeccmd[CRASHACTION_SIZE];
+static char crash_debug_debugkey[CRASHACTION_SIZE];
+
+static char *crash_action[CRASHREASON_N] = {
+    [CRASHREASON_PANIC] = crash_debug_panic,
+    [CRASHREASON_HWDOM] = crash_debug_hwdom,
+    [CRASHREASON_WATCHDOG] = crash_debug_watchdog,
+    [CRASHREASON_KEXECCMD] = crash_debug_kexeccmd,
+    [CRASHREASON_DEBUGKEY] = crash_debug_debugkey,
+};
+
+string_runtime_param("crash-debug-panic", crash_debug_panic);
+string_runtime_param("crash-debug-hwdom", crash_debug_hwdom);
+string_runtime_param("crash-debug-watchdog", crash_debug_watchdog);
+string_runtime_param("crash-debug-kexeccmd", crash_debug_kexeccmd);
+string_runtime_param("crash-debug-debugkey", crash_debug_debugkey);
+
+void keyhandler_crash_action(enum crash_reason reason)
+{
+    const char *action = crash_action[reason];
+    struct cpu_user_regs *regs = get_irq_regs() ? : guest_cpu_user_regs();
+
+    while ( *action ) {
+        if ( *action == '.' )
+            mdelay(1000);
+        else
+            handle_keypress(*action, regs);
+        action++;
+    }
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/common/shutdown.c b/xen/common/shutdown.c
index 912593915b..abde48aa4c 100644
--- a/xen/common/shutdown.c
+++ b/xen/common/shutdown.c
@@ -43,7 +43,7 @@ void hwdom_shutdown(u8 reason)
     case SHUTDOWN_crash:
         debugger_trap_immediate();
         printk("Hardware Dom%u crashed: ", hardware_domain->domain_id);
-        kexec_crash();
+        kexec_crash(CRASHREASON_HWDOM);
         maybe_reboot();
         break; /* not reached */
 
@@ -56,7 +56,7 @@ void hwdom_shutdown(u8 reason)
     case SHUTDOWN_watchdog:
         printk("Hardware Dom%u shutdown: watchdog rebooting machine\n",
                hardware_domain->domain_id);
-        kexec_crash();
+        kexec_crash(CRASHREASON_WATCHDOG);
         machine_restart(0);
         break; /* not reached */
 
diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 861ad53a8f..acec277f5e 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -1271,7 +1271,7 @@ void panic(const char *fmt, ...)
 
     debugger_trap_immediate();
 
-    kexec_crash();
+    kexec_crash(CRASHREASON_PANIC);
 
     if ( opt_noreboot )
         machine_halt();
diff --git a/xen/include/xen/kexec.h b/xen/include/xen/kexec.h
index e85ba16405..9f7a912e97 100644
--- a/xen/include/xen/kexec.h
+++ b/xen/include/xen/kexec.h
@@ -1,6 +1,8 @@
 #ifndef __XEN_KEXEC_H__
 #define __XEN_KEXEC_H__
 
+#include <xen/keyhandler.h>
+
 #ifdef CONFIG_KEXEC
 
 #include <public/kexec.h>
@@ -48,7 +50,7 @@ void machine_kexec_unload(struct kexec_image *image);
 void machine_kexec_reserved(xen_kexec_reserve_t *reservation);
 void machine_reboot_kexec(struct kexec_image *image);
 void machine_kexec(struct kexec_image *image);
-void kexec_crash(void);
+void kexec_crash(enum crash_reason reason);
 void kexec_crash_save_cpu(void);
 struct crash_xen_info *kexec_crash_save_info(void);
 void machine_crash_shutdown(void);
@@ -82,7 +84,11 @@ void vmcoreinfo_append_str(const char *fmt, ...)
 #define kexecing 0
 
 static inline void kexec_early_calculations(void) {}
-static inline void kexec_crash(void) {}
+static inline void kexec_crash(enum crash_reason reason)
+{
+    keyhandler_crash_action(reason);
+}
+
 static inline void kexec_crash_save_cpu(void) {}
 static inline void set_kexec_crash_area_size(u64 system_ram) {}
 
diff --git a/xen/include/xen/keyhandler.h b/xen/include/xen/keyhandler.h
index 5131e86cbc..dbf797a8b4 100644
--- a/xen/include/xen/keyhandler.h
+++ b/xen/include/xen/keyhandler.h
@@ -48,4 +48,15 @@ void register_irq_keyhandler(unsigned char key,
 /* Inject a keypress into the key-handling subsystem. */
 extern void handle_keypress(unsigned char key, struct cpu_user_regs *regs);
 
+enum crash_reason {
+    CRASHREASON_PANIC,
+    CRASHREASON_HWDOM,
+    CRASHREASON_WATCHDOG,
+    CRASHREASON_KEXECCMD,
+    CRASHREASON_DEBUGKEY,
+    CRASHREASON_N
+};
+
+void keyhandler_crash_action(enum crash_reason reason);
+
 #endif /* __XEN_KEYHANDLER_H__ */
-- 
2.26.2