xen: enable keyhandlers to work without register set specified

There are only two keyhandlers which make use of the cpu_user_regs
struct passed to them. In order to be able to call any keyhandler in
non-interrupt contexts, too, modify those two handlers to cope with a
NULL regs pointer by using run_in_exception_handler() in that case.

Suggested-by: Julien Grall <julien@xen.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>

xen/common/keyhandler.c

@@ -181,7 +181,10 @@ static void dump_registers(unsigned char key, struct cpu_user_regs *regs)
     cpumask_copy(&dump_execstate_mask, &cpu_online_map);
 
     /* Get local execution state out immediately, in case we get stuck. */
-    dump_execstate(regs);
+    if ( regs )
+        dump_execstate(regs);
+    else
+        run_in_exception_handler(dump_execstate);
 
     /* Alt. handling: remaining CPUs are dumped asynchronously one-by-one. */
     if ( alt_key_handling )
@@ -481,15 +484,23 @@ static void run_all_keyhandlers(unsigned char key, struct cpu_user_regs *regs)
     tasklet_schedule(&run_all_keyhandlers_tasklet);
 }
 
-static void do_debug_key(unsigned char key, struct cpu_user_regs *regs)
+static void do_debugger_trap_fatal(struct cpu_user_regs *regs)
 {
-    printk("'%c' pressed -> trapping into debugger\n", key);
     (void)debugger_trap_fatal(0xf001, regs);
 
     /* Prevent tail call optimisation, which confuses xendbg. */
     barrier();
 }
 
+static void do_debug_key(unsigned char key, struct cpu_user_regs *regs)
+{
+    printk("'%c' pressed -> trapping into debugger\n", key);
+    if ( regs )
+        do_debugger_trap_fatal(regs);
+    else
+        run_in_exception_handler(do_debugger_trap_fatal);
+}
+
 static void do_toggle_alt_key(unsigned char key, struct cpu_user_regs *regs)
 {
     alt_key_handling = !alt_key_handling;