x86: explicit call to mmiotrace in do_page_fault()

The custom page fault handler list is replaced with a single function
pointer. All related functions and variables are renamed for
mmiotrace.

Signed-off-by: Pekka Paalanen <pq@iki.fi>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: pq@iki.fi
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

3 files changed, 47 insertions, 47 deletions

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 7c6496e2225e..9491c0ae03a3 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -168,20 +168,18 @@ config IOMMU_LEAK
           Add a simple leak tracer to the IOMMU code. This is useful when you
           are debugging a buggy device driver that leaks IOMMU mappings.
 
-config PAGE_FAULT_HANDLERS
-        bool "Custom page fault handlers"
-        depends on DEBUG_KERNEL
-        help
-          Allow the use of custom page fault handlers. A kernel module may
-          register a function that is called on every page fault. Custom
-          handlers are used by some debugging and reverse engineering tools.
+config MMIOTRACE_HOOKS
+        bool
+        default n
 
 config MMIOTRACE
         tristate "Memory mapped IO tracing"
-        depends on DEBUG_KERNEL && PAGE_FAULT_HANDLERS && RELAY && DEBUG_FS
+        depends on DEBUG_KERNEL && RELAY && DEBUG_FS
+        select MMIOTRACE_HOOKS
         default n
         help
           This will build a kernel module called mmiotrace.
+          Making this a built-in is heavily discouraged.
 
           Mmiotrace traces Memory Mapped I/O access and is meant for debugging
           and reverse engineering. The kernel module offers wrapped
diff --git a/arch/x86/kernel/mmiotrace/kmmio.c b/arch/x86/kernel/mmiotrace/kmmio.c
index 28411dadb8b3..e759f7c3878f 100644
--- a/arch/x86/kernel/mmiotrace/kmmio.c
+++ b/arch/x86/kernel/mmiotrace/kmmio.c
@@ -51,10 +51,6 @@ static LIST_HEAD(kmmio_probes);
 
 static struct kmmio_context kmmio_ctx[NR_CPUS];
 
-static struct pf_handler kmmio_pf_hook = {
-        .handler = kmmio_page_fault
-};
-
 static struct notifier_block nb_die = {
         .notifier_call = kmmio_die_notifier
 };
@@ -77,7 +73,8 @@ void cleanup_kmmio(void)
          * kmmio_page_table, kmmio_probes
          */
         if (handler_registered) {
-                unregister_page_fault_handler(&kmmio_pf_hook);
+                if (mmiotrace_unregister_pf(&kmmio_page_fault))
+                        BUG();
                 synchronize_rcu();
         }
         unregister_die_notifier(&nb_die);
@@ -343,8 +340,11 @@ int register_kmmio_probe(struct kmmio_probe *p)
         }
 
         if (!handler_registered) {
-                register_page_fault_handler(&kmmio_pf_hook);
-                handler_registered++;
+                if (mmiotrace_register_pf(&kmmio_page_fault))
+                        printk(KERN_ERR "mmiotrace: Cannot register page "
+                                        "fault handler.\n");
+                else
+                        handler_registered++;
         }
 
 out:
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 343f5c1aacc8..e9a086a1a9ff 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -49,53 +49,55 @@
 #define PF_RSVD         (1<<3)
 #define PF_INSTR        (1<<4)
 
-#ifdef CONFIG_PAGE_FAULT_HANDLERS
-static HLIST_HEAD(pf_handlers); /* protected by RCU */
-static DEFINE_SPINLOCK(pf_handlers_writer);
+#ifdef CONFIG_MMIOTRACE_HOOKS
+static pf_handler_func mmiotrace_pf_handler; /* protected by RCU */
+static DEFINE_SPINLOCK(mmiotrace_handler_lock);
 
-void register_page_fault_handler(struct pf_handler *new_pfh)
+int mmiotrace_register_pf(pf_handler_func new_pfh)
 {
+        int ret = 0;
         unsigned long flags;
-        spin_lock_irqsave(&pf_handlers_writer, flags);
-        hlist_add_head_rcu(&new_pfh->hlist, &pf_handlers);
-        spin_unlock_irqrestore(&pf_handlers_writer, flags);
+        spin_lock_irqsave(&mmiotrace_handler_lock, flags);
+        if (mmiotrace_pf_handler)
+                ret = -EBUSY;
+        else
+                mmiotrace_pf_handler = new_pfh;
+        spin_unlock_irqrestore(&mmiotrace_handler_lock, flags);
+        return ret;
 }
-EXPORT_SYMBOL_GPL(register_page_fault_handler);
+EXPORT_SYMBOL_GPL(mmiotrace_register_pf);
 
 /**
- * unregister_page_fault_handler:
+ * mmiotrace_unregister_pf:
  * The caller must ensure @old_pfh is not in use anymore before freeing it.
- * This function does not guarantee it. The list of handlers is protected by
- * RCU, so you can do this by e.g. calling synchronize_rcu().
+ * This function does not guarantee it. The handler function pointer is
+ * protected by RCU, so you can do this by e.g. calling synchronize_rcu().
  */
-void unregister_page_fault_handler(struct pf_handler *old_pfh)
+int mmiotrace_unregister_pf(pf_handler_func old_pfh)
 {
+        int ret = 0;
         unsigned long flags;
-        spin_lock_irqsave(&pf_handlers_writer, flags);
-        hlist_del_rcu(&old_pfh->hlist);
-        spin_unlock_irqrestore(&pf_handlers_writer, flags);
+        spin_lock_irqsave(&mmiotrace_handler_lock, flags);
+        if (mmiotrace_pf_handler != old_pfh)
+                ret = -EPERM;
+        else
+                mmiotrace_pf_handler = NULL;
+        spin_unlock_irqrestore(&mmiotrace_handler_lock, flags);
+        return ret;
 }
-EXPORT_SYMBOL_GPL(unregister_page_fault_handler);
-#endif
+EXPORT_SYMBOL_GPL(mmiotrace_unregister_pf);
+#endif /* CONFIG_MMIOTRACE_HOOKS */
 
 /* returns non-zero if do_page_fault() should return */
-static int handle_custom_pf(struct pt_regs *regs, unsigned long error_code,
-                                                        unsigned long address)
+static inline int call_mmiotrace(struct pt_regs *regs,
+                                        unsigned long error_code,
+                                        unsigned long address)
 {
-#ifdef CONFIG_PAGE_FAULT_HANDLERS
+#ifdef CONFIG_MMIOTRACE_HOOKS
         int ret = 0;
-        struct pf_handler *cur;
-        struct hlist_node *ncur;
-
-        if (hlist_empty(&pf_handlers))
-                return 0;
-
         rcu_read_lock();
-        hlist_for_each_entry_rcu(cur, ncur, &pf_handlers, hlist) {
-                ret = cur->handler(regs, error_code, address);
-                if (ret)
-                        break;
-        }
+        if (mmiotrace_pf_handler)
+                ret = mmiotrace_pf_handler(regs, error_code, address);
         rcu_read_unlock();
         return ret;
 #else
@@ -655,7 +657,7 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 
         if (notify_page_fault(regs))
                 return;
-        if (handle_custom_pf(regs, error_code, address))
+        if (call_mmiotrace(regs, error_code, address))
                 return;
 
         /*