[PATCH v2] xen: add support for automatic debug key actions in case of crash

Juergen Gross posted 1 patch 1 week, 1 day ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/xen tags/patchew/20201120131306.24388-1-jgross@suse.com
Maintainers: Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>, Julien Grall <julien@xen.org>, Ian Jackson <iwj@xenproject.org>, Jan Beulich <jbeulich@suse.com>, Stefano Stabellini <sstabellini@kernel.org>, George Dunlap <george.dunlap@citrix.com>
docs/misc/xen-command-line.pandoc | 39 +++++++++++++++++++++++++++++++
xen/common/kexec.c                |  8 ++++---
xen/common/keyhandler.c           | 38 ++++++++++++++++++++++++++++++
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, 104 insertions(+), 8 deletions(-)

[PATCH v2] xen: add support for automatic debug key actions in case of crash

Posted by Juergen Gross 1 week, 1 day ago
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 10 millisecond pause.

So "crash-debug-watchdog=0+0qr" would result in special output in case
of watchdog triggered crash (dom0 state, 10 ms pause, dom0 state,
domain info, run queues).

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V2:
- switched special character '.' to '+' (Jan Beulich)
- 10 ms instead of 1 s pause (Jan Beulich)
- added more text to the boot parameter description (Jan Beulich)
---
 docs/misc/xen-command-line.pandoc | 39 +++++++++++++++++++++++++++++++
 xen/common/kexec.c                |  8 ++++---
 xen/common/keyhandler.c           | 38 ++++++++++++++++++++++++++++++
 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, 104 insertions(+), 8 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 4ae9391fcd..c274351aeb 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -574,6 +574,45 @@ 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 10 millisecond pause.
+
+`crash-debug-debugkey` will be used for crashes induced by the `C` debug
+key (i.e. manually induced crash).
+
+`crash-debug-hwdom` denotes a crash of dom0.
+
+`crash-debug-kexeccmd` is an explicit request of dom0 to continue with the
+kdump kernel via kexec.
+
+`crash-debug-panic` is a crash of the hypervisor.
+
+`crash-debug-watchdog` is a crash due to the watchdog timer expiring.
+
+It should be noted that dumping diagnosis data to the console can fail in
+multiple ways (missing data, hanging system, ...) depending on the reason
+of the crash, which might have left the hypervisor in a bad state.
+
+So e.g. `crash-debug-watchdog=0+0r` would dump dom0 state twice with 10
+milliseconds 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..c2da7c18a8 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 +509,42 @@ 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(10);
+        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


Re: [PATCH v2] xen: add support for automatic debug key actions in case of crash

Posted by Jan Beulich 4 days, 10 hours ago
On 20.11.2020 14:13, Juergen Gross wrote:
> @@ -507,6 +509,42 @@ 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] = {

Considering the sole use below, I think there can be two "const"
added here. With this single use I also wonder whether this
array wouldn't better be private to that function.

> +    [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);

This one probably wants a CONFIG_KEXEC conditional around it,
such that requests to set it won't appear to be "okay" on !KEXEC
builds. At which point the doc probably also wants to mention the
conditional availability of this option.

> +string_runtime_param("crash-debug-debugkey", crash_debug_debugkey);
> +
> +void keyhandler_crash_action(enum crash_reason reason)
> +{
> +    const char *action = crash_action[reason];

In order to avoid cascade problems when the system's already in
trouble, maybe better to bounds check "reason" before using as
array index and, also with the CONFIG_KEXEC related adjustment
requested above in mind, ...

> +    struct cpu_user_regs *regs = get_irq_regs() ? : guest_cpu_user_regs();
> +
> +    while ( *action )

... perhaps also better to check action against NULL before
de-referencing?

Jan

Re: [PATCH v2] xen: add support for automatic debug key actions in case of crash

Posted by Jürgen Groß 4 days, 9 hours ago
On 24.11.20 12:27, Jan Beulich wrote:
> On 20.11.2020 14:13, Juergen Gross wrote:
>> @@ -507,6 +509,42 @@ 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] = {
> 
> Considering the sole use below, I think there can be two "const"
> added here. With this single use I also wonder whether this
> array wouldn't better be private to that function.

Both fine with me.

> 
>> +    [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);
> 
> This one probably wants a CONFIG_KEXEC conditional around it,
> such that requests to set it won't appear to be "okay" on !KEXEC
> builds. At which point the doc probably also wants to mention the
> conditional availability of this option.

Yes.

> 
>> +string_runtime_param("crash-debug-debugkey", crash_debug_debugkey);
>> +
>> +void keyhandler_crash_action(enum crash_reason reason)
>> +{
>> +    const char *action = crash_action[reason];
> 
> In order to avoid cascade problems when the system's already in
> trouble, maybe better to bounds check "reason" before using as
> array index and, also with the CONFIG_KEXEC related adjustment
> requested above in mind, ...
> 
>> +    struct cpu_user_regs *regs = get_irq_regs() ? : guest_cpu_user_regs();
>> +
>> +    while ( *action )
> 
> ... perhaps also better to check action against NULL before
> de-referencing?

Okay (to both).

And I only now realized that get_irq_regs() is x86 only. I'll add a
dummy Arm function always returning NULL.


Juergen