[PATCH 1/8] limit passing around of cpu_user_regs

[Jan Beulich <jbeulich@xxxxxxxx>]

There are exactly two handlers which care about the registers. Have
handle_keypress() make the pointer available via a per-CPU variable,
thus eliminating the need to pass it to all IRQ key handlers, making
sure that a console-invoked key's handling can still nest inside a
sysctl-invoked one's.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Subsequently we may want to eliminate the fn/irq_fn union as well,
along with dropping the now redundant irq_keyhandler_fn_t.

--- a/xen/common/keyhandler.c
+++ b/xen/common/keyhandler.c
@@ -80,6 +80,7 @@ static void cf_check keypress_action(voi
 }
 
 static DECLARE_TASKLET(keypress_tasklet, keypress_action, NULL);
+static DEFINE_PER_CPU(struct cpu_user_regs *, keypress_regs);
 
 void handle_keypress(unsigned char key, struct cpu_user_regs *regs)
 {
@@ -91,7 +92,16 @@ void handle_keypress(unsigned char key,
     if ( !in_irq() || h->irq_callback )
     {
         console_start_log_everything();
-        h->irq_callback ? h->irq_fn(key, regs) : h->fn(key);
+        if ( h->irq_callback )
+        {
+            struct cpu_user_regs *old = this_cpu(keypress_regs);
+
+            this_cpu(keypress_regs) = regs;
+            h->irq_fn(key);
+            this_cpu(keypress_regs) = old;
+        }
+        else
+            h->fn(key);
         console_end_log_everything();
     }
     else
@@ -171,8 +181,7 @@ void cf_check dump_execstate(struct cpu_
     watchdog_enable();
 }
 
-static void cf_check dump_registers(
-    unsigned char key, struct cpu_user_regs *regs)
+static void cf_check dump_registers(unsigned char key)
 {
     unsigned int cpu;
 
@@ -185,8 +194,8 @@ static void cf_check dump_registers(
     cpumask_copy(&dump_execstate_mask, &cpu_online_map);
 
     /* Get local execution state out immediately, in case we get stuck. */
-    if ( regs )
-        dump_execstate(regs);
+    if ( this_cpu(keypress_regs) )
+        dump_execstate(this_cpu(keypress_regs));
     else
         run_in_exception_handler(dump_execstate);
 
@@ -248,8 +257,7 @@ static void cf_check dump_hwdom_register
     }
 }
 
-static void cf_check reboot_machine(
-    unsigned char key, struct cpu_user_regs *regs)
+static void cf_check reboot_machine(unsigned char key)
 {
     printk("'%c' pressed -> rebooting machine\n", key);
     machine_restart(0);
@@ -477,8 +485,7 @@ static void cf_check run_all_nonirq_keyh
 static DECLARE_TASKLET(run_all_keyhandlers_tasklet,
                        run_all_nonirq_keyhandlers, NULL);
 
-static void cf_check run_all_keyhandlers(
-    unsigned char key, struct cpu_user_regs *regs)
+static void cf_check run_all_keyhandlers(unsigned char key)
 {
     struct keyhandler *h;
     unsigned int k;
@@ -494,7 +501,7 @@ static void cf_check run_all_keyhandlers
         if ( !h->irq_fn || !h->diagnostic || !h->irq_callback )
             continue;
         printk("[%c: %s]\n", k, h->desc);
-        h->irq_fn(k, regs);
+        h->irq_fn(k);
     }
 
     watchdog_enable();
@@ -511,17 +518,16 @@ static void cf_check do_debugger_trap_fa
     barrier();
 }
 
-static void cf_check do_debug_key(unsigned char key, struct cpu_user_regs 
*regs)
+static void cf_check do_debug_key(unsigned char key)
 {
     printk("'%c' pressed -> trapping into debugger\n", key);
-    if ( regs )
-        do_debugger_trap_fatal(regs);
+    if ( this_cpu(keypress_regs) )
+        do_debugger_trap_fatal(this_cpu(keypress_regs));
     else
         run_in_exception_handler(do_debugger_trap_fatal);
 }
 
-static void cf_check do_toggle_alt_key(
-    unsigned char key, struct cpu_user_regs *regs)
+static void cf_check do_toggle_alt_key(unsigned char key)
 {
     alt_key_handling = !alt_key_handling;
     printk("'%c' pressed -> using %s key handling\n", key,
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -280,7 +280,7 @@ static int *__read_mostly upper_thresh_a
 static int *__read_mostly lower_thresh_adj = &xenlog_lower_thresh;
 static const char *__read_mostly thresh_adj = "standard";
 
-static void cf_check do_toggle_guest(unsigned char key, struct cpu_user_regs 
*regs)
+static void cf_check do_toggle_guest(unsigned char key)
 {
     if ( upper_thresh_adj == &xenlog_upper_thresh )
     {
@@ -307,13 +307,13 @@ static void do_adj_thresh(unsigned char
            loglvl_str(*upper_thresh_adj));
 }
 
-static void cf_check do_inc_thresh(unsigned char key, struct cpu_user_regs 
*regs)
+static void cf_check do_inc_thresh(unsigned char key)
 {
     ++*lower_thresh_adj;
     do_adj_thresh(key);
 }
 
-static void cf_check do_dec_thresh(unsigned char key, struct cpu_user_regs 
*regs)
+static void cf_check do_dec_thresh(unsigned char key)
 {
     if ( *lower_thresh_adj )
         --*lower_thresh_adj;
--- a/xen/include/xen/keyhandler.h
+++ b/xen/include/xen/keyhandler.h
@@ -24,9 +24,7 @@ typedef void (keyhandler_fn_t)(unsigned
  *
  * Called in hardirq context with interrupts disabled.
  */
-struct cpu_user_regs;
-typedef void (irq_keyhandler_fn_t)(unsigned char key,
-                                   struct cpu_user_regs *regs);
+typedef void irq_keyhandler_fn_t(unsigned char key);
 
 /* Initialize keytable with default handlers. */
 void initialize_keytable(void);
@@ -46,6 +44,7 @@ void register_irq_keyhandler(unsigned ch
                              bool diagnostic);
 
 /* Inject a keypress into the key-handling subsystem. */
+struct cpu_user_regs;
 extern void handle_keypress(unsigned char key, struct cpu_user_regs *regs);
 
 enum crash_reason {