[RFC Patch 1/4] Allow kernel-space hw-breakpoints to be restricted only for a subset of CPUs using a cpumask field in struct hw_breakpoint.

[RFC Patch 1/4] Allow kernel-space hw-breakpoints to be restricted only for a subset of CPUs using a cpumask field in struct hw_breakpoint.

[K.Prasad]

[-- Attachment #1: per_cpu_breakpoint_01 --]
[-- Type: text/plain, Size: 8494 bytes --]

Allow kernel-space hw-breakpoints to be restricted only for a subset of
CPUs using a cpumask field in 'struct hw_breakpoint'.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 arch/x86/include/asm/hw_breakpoint.h |    1 
 arch/x86/kernel/hw_breakpoint.c      |   12 +++
 include/asm-generic/hw_breakpoint.h  |    2 
 kernel/hw_breakpoint.c               |  124 +++++++++++++++++++++++++----------
 4 files changed, 104 insertions(+), 35 deletions(-)

Index: linux-2.6-tip.perf_hbkpt/arch/x86/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/arch/x86/kernel/hw_breakpoint.c
+++ linux-2.6-tip.perf_hbkpt/arch/x86/kernel/hw_breakpoint.c
@@ -68,6 +68,12 @@ static unsigned long encode_dr7(int drnu
 	return bp_info;
 }
 
+/* Disable breakpoints on the physical debug registers */
+void arch_disable_hw_breakpoint(void)
+{
+	set_debugreg(0UL, 7);
+}
+
 void arch_update_kernel_hw_breakpoint(void *unused)
 {
 	struct hw_breakpoint *bp;
@@ -78,7 +84,7 @@ void arch_update_kernel_hw_breakpoint(vo
 	set_debugreg(0UL, 7);
 
 	for (i = hbp_kernel_pos; i < HBP_NUM; i++) {
-		per_cpu(this_hbp_kernel[i], cpu) = bp = hbp_kernel[i];
+		bp = per_cpu(this_hbp_kernel[i], cpu);
 		if (bp) {
 			temp_kdr7 |= encode_dr7(i, bp->info.len, bp->info.type);
 			set_debugreg(bp->info.address, i);
@@ -207,6 +213,10 @@ int arch_validate_hwbkpt_settings(struct
 	unsigned int align;
 	int ret = -EINVAL;
 
+	/* User-space breakpoints cannot be restricted to a subset of CPUs */
+	if (tsk && bp->cpumask)
+		return ret;
+
 	switch (bp->info.type) {
 	/*
 	 * Ptrace-refactoring code
Index: linux-2.6-tip.perf_hbkpt/include/asm-generic/hw_breakpoint.h
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/include/asm-generic/hw_breakpoint.h
+++ linux-2.6-tip.perf_hbkpt/include/asm-generic/hw_breakpoint.h
@@ -8,6 +8,7 @@
 #ifdef	__KERNEL__
 #include <linux/list.h>
 #include <linux/types.h>
+#include <linux/cpumask.h>
 #include <linux/kallsyms.h>
 
 /**
@@ -102,6 +103,7 @@
  */
 struct hw_breakpoint {
 	void (*triggered)(struct hw_breakpoint *, struct pt_regs *);
+	const cpumask_t *cpumask;
 	struct arch_hw_breakpoint info;
 };
 
Index: linux-2.6-tip.perf_hbkpt/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/kernel/hw_breakpoint.c
+++ linux-2.6-tip.perf_hbkpt/kernel/hw_breakpoint.c
@@ -47,14 +47,7 @@
  */
 static DEFINE_SPINLOCK(hw_breakpoint_lock);
 
-/* Array of kernel-space breakpoint structures */
-struct hw_breakpoint *hbp_kernel[HBP_NUM];
-
-/*
- * Per-processor copy of hbp_kernel[]. Used only when hbp_kernel is being
- * modified but we need the older copy to handle any hbp exceptions. It will
- * sync with hbp_kernel[] value after updation is done through IPIs.
- */
+/* Per-cpu copy of HW-breakpoint structure */
 DEFINE_PER_CPU(struct hw_breakpoint*, this_hbp_kernel[HBP_NUM]);
 
 /*
@@ -72,6 +65,9 @@ unsigned int hbp_kernel_pos = HBP_NUM;
  */
 unsigned int hbp_user_refcount[HBP_NUM];
 
+/* An array denoting the number of consumed HW Breakpoints on each CPU */
+static DEFINE_PER_CPU(int, hbp_consumed);
+
 /*
  * Load the debug registers during startup of a CPU.
  */
@@ -294,6 +290,23 @@ void unregister_user_hw_breakpoint(struc
 }
 EXPORT_SYMBOL_GPL(unregister_user_hw_breakpoint);
 
+/* Update per-cpu instances of HW Breakpoint structure */
+static void update_each_cpu_kernel_hbp(void *bp_param)
+{
+	int i, cpu = get_cpu();
+	struct hw_breakpoint *bp = (struct hw_breakpoint *)bp_param;
+
+	for (i = HBP_NUM-1; i >= hbp_kernel_pos; i--) {
+		if (per_cpu(this_hbp_kernel[i], cpu))
+			continue;
+		per_cpu(this_hbp_kernel[i], cpu) = bp;
+		per_cpu(hbp_consumed, cpu)++;
+		break;
+	}
+	arch_update_kernel_hw_breakpoint(NULL);
+	put_cpu();
+}
+
 /**
  * register_kernel_hw_breakpoint - register a hardware breakpoint for kernel space
  * @bp: the breakpoint structure to register
@@ -305,27 +318,79 @@ EXPORT_SYMBOL_GPL(unregister_user_hw_bre
 int register_kernel_hw_breakpoint(struct hw_breakpoint *bp)
 {
 	int rc;
+	unsigned int cpu;
 
 	rc = arch_validate_hwbkpt_settings(bp, NULL);
 	if (rc)
 		return rc;
 
+	/* Default to ALL CPUs if cpumask is not specified */
+	if (!bp->cpumask)
+		bp->cpumask = cpu_possible_mask;
+
 	spin_lock_bh(&hw_breakpoint_lock);
 
-	rc = -ENOSPC;
-	/* Check if we are over-committing */
-	if ((hbp_kernel_pos > 0) && (!hbp_user_refcount[hbp_kernel_pos-1])) {
-		hbp_kernel_pos--;
-		hbp_kernel[hbp_kernel_pos] = bp;
-		on_each_cpu(arch_update_kernel_hw_breakpoint, NULL, 1);
-		rc = 0;
+	rc = -EINVAL;
+	for_each_cpu(cpu, bp->cpumask) {
+		/*
+		 * Check if we need a new slot of debug register in every CPU
+		 * i.e. if 'hbp_kernel_pos' needs to be decremented or if the
+		 * request can be serviced by consuming the vacant debug
+		 * registers
+		 */
+		if (per_cpu(hbp_consumed, cpu) == (HBP_NUM - hbp_kernel_pos)) {
+			/* Check if a new slot is available */
+			if ((hbp_kernel_pos == 0) ||
+			    (hbp_user_refcount[hbp_kernel_pos - 1] != 0)) {
+				rc = -ENOSPC;
+				goto err_ret;
+			} else {
+				hbp_kernel_pos--;
+				break;
+			}
+		}
 	}
 
+	if (cpumask_test_cpu(smp_processor_id(), bp->cpumask))
+		update_each_cpu_kernel_hbp(bp);
+	smp_call_function_many(bp->cpumask, update_each_cpu_kernel_hbp, bp, 1);
+	rc = 0;
+
+err_ret:
 	spin_unlock_bh(&hw_breakpoint_lock);
 	return rc;
 }
 EXPORT_SYMBOL_GPL(register_kernel_hw_breakpoint);
 
+/* Removes breakpoint structure from the per-cpu breakpoint data-structure */
+static void remove_each_cpu_kernel_hbp(void *bp_param)
+{
+	int i, j, cpu = get_cpu();
+	struct hw_breakpoint *bp  = (struct hw_breakpoint *)bp_param;
+
+	/*
+	 * Disable breakpoints to avoid concurrent exceptions from accessing
+	 * old or NULL breakpoint structures
+	 */
+	arch_disable_hw_breakpoint();
+	for (i = HBP_NUM-1; i >= hbp_kernel_pos; i--) {
+		if (per_cpu(this_hbp_kernel[i], cpu) == bp) {
+			/*
+			 * Shift the breakpoint structures by one-position
+			 * above to compact them
+			 */
+			for (j = i; j > hbp_kernel_pos; j--)
+				per_cpu(this_hbp_kernel[j], cpu) =
+					per_cpu(this_hbp_kernel[j-1], cpu);
+			per_cpu(this_hbp_kernel[hbp_kernel_pos], cpu) = NULL;
+			break;
+		}
+	}
+	per_cpu(hbp_consumed, cpu)--;
+	arch_update_kernel_hw_breakpoint(NULL);
+	put_cpu();
+}
+
 /**
  * unregister_kernel_hw_breakpoint - unregister a HW breakpoint for kernel space
  * @bp: the breakpoint structure to unregister
@@ -334,32 +399,23 @@ EXPORT_SYMBOL_GPL(register_kernel_hw_bre
  */
 void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp)
 {
-	int i, j;
+	int cpu;
 
 	spin_lock_bh(&hw_breakpoint_lock);
 
-	/* Find the 'bp' in our list of breakpoints for kernel */
-	for (i = hbp_kernel_pos; i < HBP_NUM; i++)
-		if (bp == hbp_kernel[i])
-			break;
+	if (cpumask_test_cpu(smp_processor_id(), bp->cpumask))
+		remove_each_cpu_kernel_hbp(bp);
+	smp_call_function_many(bp->cpumask, remove_each_cpu_kernel_hbp, bp, 1);
+	for_each_possible_cpu(cpu)
+		if (per_cpu(hbp_consumed, cpu) == (HBP_NUM - hbp_kernel_pos))
+			goto ret_path;
 
-	/* Check if we did not find a match for 'bp'. If so return early */
-	if (i == HBP_NUM) {
-		spin_unlock_bh(&hw_breakpoint_lock);
-		return;
-	}
-
-	/*
-	 * We'll shift the breakpoints one-level above to compact if
-	 * unregistration creates a hole
-	 */
-	for (j = i; j > hbp_kernel_pos; j--)
-		hbp_kernel[j] = hbp_kernel[j-1];
+	if (bp->cpumask == cpu_possible_mask)
+		bp->cpumask = NULL;
 
-	hbp_kernel[hbp_kernel_pos] = NULL;
-	on_each_cpu(arch_update_kernel_hw_breakpoint, NULL, 1);
 	hbp_kernel_pos++;
 
+ret_path:
 	spin_unlock_bh(&hw_breakpoint_lock);
 }
 EXPORT_SYMBOL_GPL(unregister_kernel_hw_breakpoint);
Index: linux-2.6-tip.perf_hbkpt/arch/x86/include/asm/hw_breakpoint.h
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/arch/x86/include/asm/hw_breakpoint.h
+++ linux-2.6-tip.perf_hbkpt/arch/x86/include/asm/hw_breakpoint.h
@@ -48,6 +48,7 @@ extern int arch_validate_hwbkpt_settings
 extern void arch_update_user_hw_breakpoint(int pos, struct task_struct *tsk);
 extern void arch_flush_thread_hw_breakpoint(struct task_struct *tsk);
 extern void arch_update_kernel_hw_breakpoint(void *);
+extern void arch_disable_hw_breakpoint(void);
 extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
 				     unsigned long val, void *data);
 #endif	/* __KERNEL__ */

[RFC Patch 2/4] Allow breakpoints to be enabled/disabled without yielding the breakpoint request through new APIs - <enable><disable>_hw_breakpoint()

[K.Prasad]

[-- Attachment #1: enable_disable_patch_03 --]
[-- Type: text/plain, Size: 4714 bytes --]

Allow breakpoints to be enabled/disabled without yielding the
breakpoint request through new APIs - <enable><disable>_hw_breakpoint()

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 arch/x86/kernel/hw_breakpoint.c     |   15 ++++++++++-----
 include/asm-generic/hw_breakpoint.h |   13 +++++++++++++
 kernel/hw_breakpoint.c              |   27 +++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 5 deletions(-)

Index: linux-2.6-tip.perf_hbkpt/arch/x86/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/arch/x86/kernel/hw_breakpoint.c
+++ linux-2.6-tip.perf_hbkpt/arch/x86/kernel/hw_breakpoint.c
@@ -85,10 +85,11 @@ void arch_update_kernel_hw_breakpoint(vo
 
 	for (i = hbp_kernel_pos; i < HBP_NUM; i++) {
 		bp = per_cpu(this_hbp_kernel[i], cpu);
-		if (bp) {
+		if (!bp)
+			continue;
+		set_debugreg(bp->info.address, i);
+		if (atomic_read(&bp->enabled) == BP_ENABLED)
 			temp_kdr7 |= encode_dr7(i, bp->info.len, bp->info.type);
-			set_debugreg(bp->info.address, i);
-		}
 	}
 
 	/* No need to set DR6. Update the debug registers with kernel-space
@@ -288,8 +289,9 @@ void arch_update_user_hw_breakpoint(int 
 	thread->debugreg7 &= ~dr7_masks[pos];
 	if (bp) {
 		thread->debugreg[pos] = bp->info.address;
-		thread->debugreg7 |= encode_dr7(pos, bp->info.len,
-							bp->info.type);
+		if (atomic_read(&bp->enabled) == BP_ENABLED)
+			thread->debugreg7 |= encode_dr7(pos, bp->info.len,
+								bp->info.type);
 	} else
 		thread->debugreg[pos] = 0;
 }
@@ -377,6 +379,9 @@ static int __kprobes hw_breakpoint_handl
 		 */
 		if (!bp)
 			continue;
+		/* Ignore exceptions due to disabled breakpoints */
+		if (atomic_read(&bp->enabled) == BP_DISABLED)
+			continue;
 
 		(bp->triggered)(bp, args->regs);
 	}
Index: linux-2.6-tip.perf_hbkpt/include/asm-generic/hw_breakpoint.h
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/include/asm-generic/hw_breakpoint.h
+++ linux-2.6-tip.perf_hbkpt/include/asm-generic/hw_breakpoint.h
@@ -102,11 +102,22 @@
  * ----------------------------------------------------------------------
  */
 struct hw_breakpoint {
+	/*
+	 * Denotes if a breakpoint is currently enabled in physical debug
+	 * registers. Not to be set directly by the end-user. Must be
+	 * operated through <enable><disable>_hw_breakpoint() APIs only.
+	 */
+	atomic_t enabled;
 	void (*triggered)(struct hw_breakpoint *, struct pt_regs *);
 	const cpumask_t *cpumask;
 	struct arch_hw_breakpoint info;
 };
 
+enum bp_status {
+	BP_DISABLED	= 0,
+	BP_ENABLED	= 1
+};
+
 /*
  * len and type values are defined in include/asm/hw_breakpoint.h.
  * Available values vary according to the architecture.  On i386 the
@@ -135,6 +146,8 @@ extern void unregister_user_hw_breakpoin
 extern int register_kernel_hw_breakpoint(struct hw_breakpoint *bp);
 extern void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp);
 
+extern void enable_hw_breakpoint(struct hw_breakpoint *bp);
+extern void disable_hw_breakpoint(struct hw_breakpoint *bp);
 extern unsigned int hbp_kernel_pos;
 
 #endif	/* __KERNEL__ */
Index: linux-2.6-tip.perf_hbkpt/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/kernel/hw_breakpoint.c
+++ linux-2.6-tip.perf_hbkpt/kernel/hw_breakpoint.c
@@ -351,6 +351,7 @@ int register_kernel_hw_breakpoint(struct
 		}
 	}
 
+	atomic_set(&bp->enabled, BP_ENABLED);
 	if (cpumask_test_cpu(smp_processor_id(), bp->cpumask))
 		update_each_cpu_kernel_hbp(bp);
 	smp_call_function_many(bp->cpumask, update_each_cpu_kernel_hbp, bp, 1);
@@ -420,6 +421,32 @@ ret_path:
 }
 EXPORT_SYMBOL_GPL(unregister_kernel_hw_breakpoint);
 
+/**
+ * enable_hw_breakpoint - re-enable a breakpoint previously disabled
+ * @bp: pointer to the breakpoint structure to be enabled
+ *
+ * Re-enable or disable a breakpoint, previously disabled using
+ * disable_hw_breakpoint()
+ */
+void enable_hw_breakpoint(struct hw_breakpoint *bp)
+{
+	atomic_set(&bp->enabled, BP_ENABLED);
+}
+EXPORT_SYMBOL_GPL(enable_hw_breakpoint);
+
+/**
+ * disable_hw_breakpoint - disable a breakpoint from raising breakpoint exceptions
+ * @bp: pointer to the breakpoint structure to be disabled
+ *
+ * Disable a breakpoint without actually losing the registration. Re-enable it
+ * again using enable_hw_breakpoint()
+ */
+void disable_hw_breakpoint(struct hw_breakpoint *bp)
+{
+	atomic_set(&bp->enabled, BP_DISABLED);
+}
+EXPORT_SYMBOL_GPL(disable_hw_breakpoint);
+
 static struct notifier_block hw_breakpoint_exceptions_nb = {
 	.notifier_call = hw_breakpoint_exceptions_notify,
 	/* we need to be notified first */

Re: [RFC Patch 2/4] Allow breakpoints to be enabled/disabled without yielding the breakpoint request through new APIs - <enable><disable>_hw_breakpoint()

[Steven Rostedt]

On Tue, 2009-10-27 at 02:49 +0530, K.Prasad wrote:

> Index: linux-2.6-tip.perf_hbkpt/include/asm-generic/hw_breakpoint.h
> ===================================================================
> --- linux-2.6-tip.perf_hbkpt.orig/include/asm-generic/hw_breakpoint.h
> +++ linux-2.6-tip.perf_hbkpt/include/asm-generic/hw_breakpoint.h
> @@ -102,11 +102,22 @@
>   * ----------------------------------------------------------------------
>   */
>  struct hw_breakpoint {
> +	/*
> +	 * Denotes if a breakpoint is currently enabled in physical debug
> +	 * registers. Not to be set directly by the end-user. Must be
> +	 * operated through <enable><disable>_hw_breakpoint() APIs only.
> +	 */
> +	atomic_t enabled;

Just a nit, but by looking at this structure as a whole, it's not easy
to see that the above comment is talking just about the "enabled" part
of the structure or the entire structure itself.

Probably want to add ...

	/*
	 * The enabled item denotes if ...


-- Steve

>  	void (*triggered)(struct hw_breakpoint *, struct pt_regs *);
>  	const cpumask_t *cpumask;
>  	struct arch_hw_breakpoint info;
>  };
>  
> +enum bp_status {
> +	BP_DISABLED	= 0,
> +	BP_ENABLED	= 1
> +};
> +

Re: [RFC Patch 2/4] Allow breakpoints to be enabled/disabled without yielding the breakpoint request through new APIs - <enable><disable>_hw_breakpoint()

[K.Prasad]

On Wed, Oct 28, 2009 at 04:31:49PM -0400, Steven Rostedt wrote:
> On Tue, 2009-10-27 at 02:49 +0530, K.Prasad wrote:
> 
> > Index: linux-2.6-tip.perf_hbkpt/include/asm-generic/hw_breakpoint.h
> > ===================================================================
> > --- linux-2.6-tip.perf_hbkpt.orig/include/asm-generic/hw_breakpoint.h
> > +++ linux-2.6-tip.perf_hbkpt/include/asm-generic/hw_breakpoint.h
> > @@ -102,11 +102,22 @@
> >   * ----------------------------------------------------------------------
> >   */
> >  struct hw_breakpoint {
> > +	/*
> > +	 * Denotes if a breakpoint is currently enabled in physical debug
> > +	 * registers. Not to be set directly by the end-user. Must be
> > +	 * operated through <enable><disable>_hw_breakpoint() APIs only.
> > +	 */
> > +	atomic_t enabled;
> 
> Just a nit, but by looking at this structure as a whole, it's not easy
> to see that the above comment is talking just about the "enabled" part
> of the structure or the entire structure itself.
> 
> Probably want to add ...
> 
> 	/*
> 	 * The enabled item denotes if ...
> 
> 
> -- Steve
>

I will modify the comments to read as under...the role of the 'enabled'
flag has undergone changes and the comments will reflect that.


 struct hw_breakpoint {
+	/*
+	 * The 'enabled' flag denotes if a breakpoint hit would in-turn invoke
+	 * the 'triggered' function. Not to be set directly by the end-user.
+	 * Must be operated through <enable><disable>_hw_breakpoint() APIs only.
+	 */
+	atomic_t enabled;
 	void (*triggered)(struct hw_breakpoint *, struct pt_regs *);
 	const cpumask_t *cpumask;
 	struct arch_hw_breakpoint info;

Thanks,
K.Prasad

[RFC Patch 3/4] Bugfix HW-BKPT: Fix traceback seen when resuming after suspend-to-ram

[K.Prasad]

[-- Attachment #1: s2r_patch.txt --]
[-- Type: text/plain, Size: 2062 bytes --]

Load the debug registers (when a CPU turns online) through a tasklet. This
helps to keep routines (using protected hw-breakpoint data) to be invoked
only from non-interrupt context, thus making the spin_lock_bh() locking
sufficient.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 kernel/hw_breakpoint.c |   26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

Index: linux-2.6-tip.perf_hbkpt/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/kernel/hw_breakpoint.c
+++ linux-2.6-tip.perf_hbkpt/kernel/hw_breakpoint.c
@@ -23,6 +23,7 @@
  * This file contains the arch-independent routines.
  */
 
+#include <linux/interrupt.h>
 #include <linux/irqflags.h>
 #include <linux/kallsyms.h>
 #include <linux/notifier.h>
@@ -69,20 +70,19 @@ unsigned int hbp_user_refcount[HBP_NUM];
 static DEFINE_PER_CPU(int, hbp_consumed);
 
 /*
- * Load the debug registers during startup of a CPU.
+ * A tasklet to populate the debug register's values from the
+ * breakpoint structure
  */
-void load_debug_registers(void)
+static struct tasklet_struct hbp_tasklet;
+
+/* Tasklet function that populates the debug registers */
+void hbp_tasklet_function(unsigned long unused)
 {
-	unsigned long flags;
 	struct task_struct *tsk = current;
 
 	spin_lock_bh(&hw_breakpoint_lock);
 
-	/* Prevent IPIs for new kernel breakpoint updates */
-	local_irq_save(flags);
 	arch_update_kernel_hw_breakpoint(NULL);
-	local_irq_restore(flags);
-
 	if (test_tsk_thread_flag(tsk, TIF_DEBUG))
 		arch_install_thread_hw_breakpoint(tsk);
 
@@ -90,6 +90,18 @@ void load_debug_registers(void)
 }
 
 /*
+ * Load the debug registers during startup of a CPU.
+ */
+void load_debug_registers(void)
+{
+	unsigned long flags;
+
+	if (!hbp_tasklet.func)
+		tasklet_init(&hbp_tasklet, &hbp_tasklet_function, 0UL);
+	tasklet_schedule(&hbp_tasklet);
+}
+
+/*
  * Erase all the hardware breakpoint info associated with a thread.
  *
  * If tsk != current then tsk must not be usable (for example, a

[RFC Patch 4/4] Enable perf-events to use hw-breakpoints

[K.Prasad]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: perf_hbkpt_integration_04 --]
[-- Type: text/plain; charset=utf-8, Size: 8072 bytes --]

Enable perf-events to collect memory access statistics on kernel-space
data in the context of a running process.

TODO: Fix issues caused by this patch to parsing of other events.
Allow kernel-space addresses to be specified in addition to symbol name.
Fix the issues seen with the target process when run through perf.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 include/linux/perf_event.h     |   17 ++++++
 kernel/perf_event.c            |  101 ++++++++++++++++++++++++++++++++++++++++-
 tools/perf/util/parse-events.c |   42 +++++++++++++++++
 3 files changed, 159 insertions(+), 1 deletion(-)

Index: linux-2.6-tip.perf_hbkpt/include/linux/perf_event.h
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/include/linux/perf_event.h
+++ linux-2.6-tip.perf_hbkpt/include/linux/perf_event.h
@@ -31,6 +31,7 @@ enum perf_type_id {
 	PERF_TYPE_TRACEPOINT			= 2,
 	PERF_TYPE_HW_CACHE			= 3,
 	PERF_TYPE_RAW				= 4,
+	PERF_TYPE_BREAKPOINT			= 5,
 
 	PERF_TYPE_MAX,				/* non-ABI */
 };
@@ -106,6 +107,14 @@ enum perf_sw_ids {
 	PERF_COUNT_SW_MAX,			/* non-ABI */
 };
 
+/* Various breakpoint types for monitoring accesses over variables */
+enum perf_bp_id {
+	PERF_COUNT_BP_WRITE		= 0,
+	PERF_COUNT_BP_RW		= 1,
+
+	PERF_COUNT_BP_MAX,		/* non-ABI */
+};
+
 /*
  * Bits that can be set in attr.sample_type to request information
  * in the overflow packets.
@@ -207,6 +216,10 @@ struct perf_event_attr {
 		__u32		wakeup_events;	  /* wakeup every n events */
 		__u32		wakeup_watermark; /* bytes before wakeup   */
 	};
+
+	/* Store the symbol name for breakpoint request */
+	char			ksym_name[128];
+
 	__u32			__reserved_2;
 
 	__u64			__reserved_3;
@@ -476,6 +489,10 @@ struct hw_perf_event {
 			s64		remaining;
 			struct hrtimer	hrtimer;
 		};
+		struct { /* hardware breakpoints */
+			struct hw_breakpoint	*bp;
+			int			counter;
+		};
 	};
 	atomic64_t			prev_count;
 	u64				sample_period;
Index: linux-2.6-tip.perf_hbkpt/kernel/perf_event.c
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/kernel/perf_event.c
+++ linux-2.6-tip.perf_hbkpt/kernel/perf_event.c
@@ -4,7 +4,7 @@
  *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
  *  Copyright (C) 2008-2009 Red Hat, Inc., Ingo Molnar
  *  Copyright (C) 2008-2009 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
- *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
+ *  Copyright  �  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
  *
  * For licensing details see kernel-base/COPYING
  */
@@ -31,6 +31,7 @@
 #include <linux/ftrace_event.h>
 
 #include <asm/irq_regs.h>
+#include <asm/hw_breakpoint.h>
 
 /*
  * Each CPU has a list of per CPU events:
@@ -4124,6 +4125,27 @@ static const struct pmu perf_ops_task_cl
 	.read		= task_clock_perf_event_read,
 };
 
+static int breakpoint_perf_event_enable(struct perf_event *event)
+{
+	enable_hw_breakpoint(event->hw.bp);
+	return 0;
+}
+
+static void breakpoint_perf_event_disable(struct perf_event *event)
+{
+	disable_hw_breakpoint(event->hw.bp);
+}
+
+static void breakpoint_perf_event_read(struct perf_event *event)
+{
+}
+
+static const struct pmu perf_ops_breakpoint = {
+	.enable		= breakpoint_perf_event_enable,
+	.disable	= breakpoint_perf_event_disable,
+	.read		= breakpoint_perf_event_read,
+};
+
 #ifdef CONFIG_EVENT_PROFILE
 
 void perf_tp_event(int event_id, u64 addr, u64 count, void *record,
@@ -4285,6 +4307,79 @@ static const struct pmu *sw_perf_event_i
 	return pmu;
 }
 
+static void perf_breakpoint_handler(struct hw_breakpoint *bp,
+					struct pt_regs *regs)
+{
+	int event_id = 0;
+
+	switch (bp->info.type) {
+	case HW_BREAKPOINT_WRITE:
+		event_id = PERF_COUNT_BP_WRITE;
+		break;
+
+	case HW_BREAKPOINT_RW:
+		event_id = PERF_COUNT_BP_RW;
+		break;
+
+	default:
+		return;
+	}
+
+	do_perf_sw_event(PERF_TYPE_BREAKPOINT, event_id, 1, 1,
+			 NULL, regs);
+}
+
+static void breakpoint_perf_event_destroy(struct perf_event *event)
+{
+	struct hw_breakpoint *bp = event->hw.bp;
+
+	unregister_kernel_hw_breakpoint(bp);
+	kfree(bp);
+}
+
+static const struct pmu *breakpoint_perf_event_init(struct perf_event *event,
+						    int cpu, gfp_t gfpflags)
+{
+	int ret;
+	struct perf_event_attr *attr = &event->attr;
+	u64 event_id = attr->config;
+	struct hw_breakpoint *bp;
+
+	bp = event->hw.bp = kzalloc(sizeof(struct hw_breakpoint), gfpflags);
+	if (!bp)
+		return ERR_PTR(-ENOMEM);
+
+	switch (event_id) {
+
+	case PERF_COUNT_BP_WRITE:
+		bp->info.type = HW_BREAKPOINT_WRITE;
+		break;
+	case PERF_COUNT_BP_RW:
+		bp->info.type = HW_BREAKPOINT_RW;
+		break;
+	default:
+		return ERR_PTR(-EINVAL);
+	}
+
+	bp->info.len = HW_BREAKPOINT_LEN_1;
+	bp->triggered = perf_breakpoint_handler;
+
+	if (attr->ksym_name)
+		bp->info.name = attr->ksym_name;
+	else
+		return ERR_PTR(-EINVAL);
+
+	if (cpu != -1)
+		bp->cpumask = cpumask_of(cpu);
+
+	ret = register_kernel_hw_breakpoint(bp);
+	if (ret)
+		return ERR_PTR(ret);
+
+	event->destroy = breakpoint_perf_event_destroy;
+	return &perf_ops_breakpoint;
+}
+
 /*
  * Allocate and initialize a event structure
  */
@@ -4370,6 +4465,10 @@ perf_event_alloc(struct perf_event_attr 
 		pmu = tp_perf_event_init(event);
 		break;
 
+	case PERF_TYPE_BREAKPOINT:
+		pmu = breakpoint_perf_event_init(event, cpu, gfpflags);
+		break;
+
 	default:
 		break;
 	}
Index: linux-2.6-tip.perf_hbkpt/tools/perf/util/parse-events.c
===================================================================
--- linux-2.6-tip.perf_hbkpt.orig/tools/perf/util/parse-events.c
+++ linux-2.6-tip.perf_hbkpt/tools/perf/util/parse-events.c
@@ -30,6 +30,7 @@ char debugfs_path[MAXPATHLEN];
 
 #define CHW(x) .type = PERF_TYPE_HARDWARE, .config = PERF_COUNT_HW_##x
 #define CSW(x) .type = PERF_TYPE_SOFTWARE, .config = PERF_COUNT_SW_##x
+#define CBP(x) .type = PERF_TYPE_BREAKPOINT, .config = PERF_COUNT_BP_##x
 
 static struct event_symbol event_symbols[] = {
   { CHW(CPU_CYCLES),		"cpu-cycles",		"cycles"	},
@@ -47,6 +48,9 @@ static struct event_symbol event_symbols
   { CSW(PAGE_FAULTS_MAJ),	"major-faults",		""		},
   { CSW(CONTEXT_SWITCHES),	"context-switches",	"cs"		},
   { CSW(CPU_MIGRATIONS),	"cpu-migrations",	"migrations"	},
+
+  { CBP(WRITE),			"breakpoint-write",	""		},
+  { CBP(RW),			"breakpoint-readwrite", ""		},
 };
 
 #define __PERF_EVENT_FIELD(config, name) \
@@ -77,6 +81,11 @@ static const char *sw_event_names[] = {
 	"major-faults",
 };
 
+static const char *hbp_event_names[] = {
+	"breakpoint-write",
+	"breakpoint-readwrite",
+};
+
 #define MAX_ALIASES 8
 
 static const char *hw_cache[][MAX_ALIASES] = {
@@ -322,6 +331,9 @@ const char *__event_name(int type, u64 c
 	case PERF_TYPE_TRACEPOINT:
 		return tracepoint_id_to_name(config);
 
+	case PERF_TYPE_BREAKPOINT:
+		return hbp_event_names[config];
+
 	default:
 		break;
 	}
@@ -621,6 +633,31 @@ parse_numeric_event(const char **strp, s
 }
 
 static enum event_result
+parse_hbp_event(const char **strp, struct perf_event_attr *attr)
+{
+	unsigned int i, flag = 0;
+
+	char *bp_data = (char *)(*strp);
+	char *bp_event_name = strsep(&bp_data, ":");
+
+	for (i = 0; i < ARRAY_SIZE(hbp_event_names); i++) {
+		if (strncmp(bp_event_name, hbp_event_names[i],
+						strlen(bp_event_name)))
+			continue;
+		attr->config = i;
+		flag = 1;
+	}
+	if (flag == 0)
+		return EVT_FAILED;
+
+	attr->type = PERF_TYPE_BREAKPOINT;
+	strcpy(attr->ksym_name, bp_data);
+	*strp = (*strp) + strlen(*strp) + strlen(bp_data) + 1;
+
+	return EVT_HANDLED;
+}
+
+static enum event_result
 parse_event_modifier(const char **strp, struct perf_event_attr *attr)
 {
 	const char *str = *strp;
@@ -670,6 +707,10 @@ parse_event_symbols(const char **str, st
 	if (ret != EVT_FAILED)
 		goto modifier;
 
+	ret = parse_hbp_event(str, attr);
+	if (ret != EVT_FAILED)
+		goto modifier;
+
 	ret = parse_symbolic_event(str, attr);
 	if (ret != EVT_FAILED)
 		goto modifier;
@@ -773,6 +814,7 @@ static const char * const event_type_des
 	"Software event",
 	"Tracepoint event",
 	"Hardware cache event",
+	"Breakpoint event"
 };
 
 /*