x86: mmiotrace, preview 2

Kconfig.debug, Makefile and testmmiotrace.c style fixes.
Use real mutex instead of mutex.
Fix failure path in register probe func.
kmmio: RCU read-locked over single stepping.
Generate mapping id's.
Make mmio-mod.c built-in and rewrite its locking.
Add debugfs file to enable/disable mmiotracing.
kmmio: use irqsave spinlocks.
Lots of cleanups in mmio-mod.c
Marker file moved from /proc into debugfs.
Call mmiotrace entrypoints directly from ioremap.c.

Signed-off-by: Pekka Paalanen <pq@iki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/Kconfig.debug

@@ -170,30 +170,26 @@ config IOMMU_LEAK
 
 config MMIOTRACE_HOOKS
 	bool
-	default n
 
 config MMIOTRACE
-	tristate "Memory mapped IO tracing"
+	bool "Memory mapped IO tracing"
 	depends on DEBUG_KERNEL && RELAY && DEBUG_FS
 	select MMIOTRACE_HOOKS
-	default n
+	default y
 	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
-	  versions of the ioremap family of functions. The driver to be traced
-	  must be modified to call these wrappers. A user space program is
-	  required to collect the MMIO data.
+	  Mmiotrace traces Memory Mapped I/O access and is meant for
+	  debugging and reverse engineering. It is called from the ioremap
+	  implementation and works via page faults. A user space program is
+	  required to collect the MMIO data from debugfs files.
+	  Tracing is disabled by default and can be enabled from a debugfs
+	  file.
 
 	  See http://nouveau.freedesktop.org/wiki/MmioTrace
 	  If you are not helping to develop drivers, say N.
 
 config MMIOTRACE_TEST
 	tristate "Test module for mmiotrace"
 	depends on MMIOTRACE && m
-	default n
 	help
 	  This is a dumb module for testing mmiotrace. It is very dangerous
 	  as it will write garbage to IO memory starting at a given address.

arch/x86/kernel/mmiotrace/Makefile

@@ -1,4 +1,4 @@
 obj-$(CONFIG_MMIOTRACE_HOOKS)	+= kmmio.o
 obj-$(CONFIG_MMIOTRACE)		+= mmiotrace.o
-mmiotrace-objs			:= pf_in.o mmio-mod.o
+mmiotrace-y			:= pf_in.o mmio-mod.o
 obj-$(CONFIG_MMIOTRACE_TEST)	+= testmmiotrace.o

arch/x86/kernel/mmiotrace/kmmio.c

@@ -19,6 +19,7 @@
 #include <linux/preempt.h>
 #include <linux/percpu.h>
 #include <linux/kdebug.h>
+#include <linux/mutex.h>
 #include <asm/io.h>
 #include <asm/cacheflush.h>
 #include <asm/errno.h>
@@ -59,7 +60,7 @@ struct kmmio_context {
 static int kmmio_die_notifier(struct notifier_block *nb, unsigned long val,
 								void *args);
 
-static DECLARE_MUTEX(kmmio_init_mutex);
+static DEFINE_MUTEX(kmmio_init_mutex);
 static DEFINE_SPINLOCK(kmmio_lock);
 
 /* These are protected by kmmio_lock */
@@ -90,7 +91,7 @@ static struct notifier_block nb_die = {
  */
 void reference_kmmio(void)
 {
-	down(&kmmio_init_mutex);
+	mutex_lock(&kmmio_init_mutex);
 	spin_lock_irq(&kmmio_lock);
 	if (!kmmio_initialized) {
 		int i;
@@ -101,7 +102,7 @@ void reference_kmmio(void)
 	}
 	kmmio_initialized++;
 	spin_unlock_irq(&kmmio_lock);
-	up(&kmmio_init_mutex);
+	mutex_unlock(&kmmio_init_mutex);
 }
 EXPORT_SYMBOL_GPL(reference_kmmio);
 
@@ -115,7 +116,7 @@ void unreference_kmmio(void)
 {
 	bool unreg = false;
 
-	down(&kmmio_init_mutex);
+	mutex_lock(&kmmio_init_mutex);
 	spin_lock_irq(&kmmio_lock);
 
 	if (kmmio_initialized == 1) {
@@ -128,7 +129,7 @@ void unreference_kmmio(void)
 
 	if (unreg)
 		unregister_die_notifier(&nb_die); /* calls sync_rcu() */
-	up(&kmmio_init_mutex);
+	mutex_unlock(&kmmio_init_mutex);
 }
 EXPORT_SYMBOL(unreference_kmmio);
 
@@ -244,17 +245,13 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
 	 * Preemption is now disabled to prevent process switch during
 	 * single stepping. We can only handle one active kmmio trace
 	 * per cpu, so ensure that we finish it before something else
-	 * gets to run.
-	 *
-	 * XXX what if an interrupt occurs between returning from
-	 * do_page_fault() and entering the single-step exception handler?
-	 * And that interrupt triggers a kmmio trap?
-	 * XXX If we tracing an interrupt service routine or whatever, is
-	 * this enough to keep it on the current cpu?
+	 * gets to run. We also hold the RCU read lock over single
+	 * stepping to avoid looking up the probe and kmmio_fault_page
+	 * again.
 	 */
 	preempt_disable();
-
 	rcu_read_lock();
+
 	faultpage = get_kmmio_fault_page(addr);
 	if (!faultpage) {
 		/*
@@ -287,14 +284,24 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
 	if (ctx->probe && ctx->probe->pre_handler)
 		ctx->probe->pre_handler(ctx->probe, regs, addr);
 
+	/*
+	 * Enable single-stepping and disable interrupts for the faulting
+	 * context. Local interrupts must not get enabled during stepping.
+	 */
 	regs->flags |= TF_MASK;
 	regs->flags &= ~IF_MASK;
 
 	/* Now we set present bit in PTE and single step. */
 	disarm_kmmio_fault_page(ctx->fpage->page, NULL);
 
+	/*
+	 * If another cpu accesses the same page while we are stepping,
+	 * the access will not be caught. It will simply succeed and the
+	 * only downside is we lose the event. If this becomes a problem,
+	 * the user should drop to single cpu before tracing.
+	 */
+
 	put_cpu_var(kmmio_ctx);
-	rcu_read_unlock();
 	return 1;
 
 no_kmmio_ctx:
@@ -313,39 +320,23 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
 static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
 {
 	int ret = 0;
-	struct kmmio_probe *probe;
-	struct kmmio_fault_page *faultpage;
 	struct kmmio_context *ctx = &get_cpu_var(kmmio_ctx);
 
 	if (!ctx->active)
 		goto out;
 
-	rcu_read_lock();
-
-	faultpage = get_kmmio_fault_page(ctx->addr);
-	probe = get_kmmio_probe(ctx->addr);
-	if (faultpage != ctx->fpage || probe != ctx->probe) {
-		/*
-		 * The trace setup changed after kmmio_handler() and before
-		 * running this respective post handler. User does not want
-		 * the result anymore.
-		 */
-		ctx->probe = NULL;
-		ctx->fpage = NULL;
-	}
-
 	if (ctx->probe && ctx->probe->post_handler)
 		ctx->probe->post_handler(ctx->probe, condition, regs);
 
-	if (ctx->fpage)
-		arm_kmmio_fault_page(ctx->fpage->page, NULL);
+	arm_kmmio_fault_page(ctx->fpage->page, NULL);
 
 	regs->flags &= ~TF_MASK;
 	regs->flags |= ctx->saved_flags;
 
 	/* These were acquired in kmmio_handler(). */
 	ctx->active--;
 	BUG_ON(ctx->active);
+	rcu_read_unlock();
 	preempt_enable_no_resched();
 
 	/*
@@ -355,8 +346,6 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
 	 */
 	if (!(regs->flags & TF_MASK))
 		ret = 1;
-
-	rcu_read_unlock();
 out:
 	put_cpu_var(kmmio_ctx);
 	return ret;
@@ -411,23 +400,24 @@ static void release_kmmio_fault_page(unsigned long page,
 
 int register_kmmio_probe(struct kmmio_probe *p)
 {
+	unsigned long flags;
 	int ret = 0;
 	unsigned long size = 0;
 
-	spin_lock_irq(&kmmio_lock);
-	kmmio_count++;
+	spin_lock_irqsave(&kmmio_lock, flags);
 	if (get_kmmio_probe(p->addr)) {
 		ret = -EEXIST;
 		goto out;
 	}
+	kmmio_count++;
 	list_add_rcu(&p->list, &kmmio_probes);
 	while (size < p->len) {
 		if (add_kmmio_fault_page(p->addr + size))
 			pr_err("kmmio: Unable to set page fault.\n");
 		size += PAGE_SIZE;
 	}
 out:
-	spin_unlock_irq(&kmmio_lock);
+	spin_unlock_irqrestore(&kmmio_lock, flags);
 	/*
 	 * XXX: What should I do here?
 	 * Here was a call to global_flush_tlb(), but it does not exist
@@ -478,7 +468,8 @@ static void remove_kmmio_fault_pages(struct rcu_head *head)
 
 /*
  * Remove a kmmio probe. You have to synchronize_rcu() before you can be
- * sure that the callbacks will not be called anymore.
+ * sure that the callbacks will not be called anymore. Only after that
+ * you may actually release your struct kmmio_probe.
  *
  * Unregistering a kmmio fault page has three steps:
  * 1. release_kmmio_fault_page()
@@ -490,18 +481,19 @@ static void remove_kmmio_fault_pages(struct rcu_head *head)
  */
 void unregister_kmmio_probe(struct kmmio_probe *p)
 {
+	unsigned long flags;
 	unsigned long size = 0;
 	struct kmmio_fault_page *release_list = NULL;
 	struct kmmio_delayed_release *drelease;
 
-	spin_lock_irq(&kmmio_lock);
+	spin_lock_irqsave(&kmmio_lock, flags);
 	while (size < p->len) {
 		release_kmmio_fault_page(p->addr + size, &release_list);
 		size += PAGE_SIZE;
 	}
 	list_del_rcu(&p->list);
 	kmmio_count--;
-	spin_unlock_irq(&kmmio_lock);
+	spin_unlock_irqrestore(&kmmio_lock, flags);
 
 	drelease = kmalloc(sizeof(*drelease), GFP_ATOMIC);
 	if (!drelease) {