[Patch 1/4] Allow arch-specific cleanup before breakpoint unregistration

[Patch 1/4] Allow arch-specific cleanup before breakpoint unregistration

[K.Prasad]

Certain architectures (such as PowerPC Book III S) have a need to cleanup
data-structures before the breakpoint is unregistered. This patch introduces
an arch-specific hook in release_bp_slot() along with a weak definition in
the form of a stub funciton.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 kernel/hw_breakpoint.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

Index: linux-2.6.ppc64_test/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6.ppc64_test.orig/kernel/hw_breakpoint.c
+++ linux-2.6.ppc64_test/kernel/hw_breakpoint.c
@@ -242,6 +242,17 @@ toggle_bp_slot(struct perf_event *bp, bo
 }
 
 /*
+ * Function to perform processor-specific cleanup during unregistration
+ */
+__weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
+{
+	/*
+	 * A weak stub function here for those archs that don't define
+	 * it inside arch/.../kernel/hw_breakpoint.c
+	 */
+}
+
+/*
  * Contraints to check before allowing this new breakpoint counter:
  *
  *  == Non-pinned counter == (Considered as pinned for now)
@@ -339,6 +350,7 @@ void release_bp_slot(struct perf_event *
 {
 	mutex_lock(&nr_bp_mutex);
 
+	arch_unregister_hw_breakpoint(bp);
 	__release_bp_slot(bp);
 
 	mutex_unlock(&nr_bp_mutex);

[Patch 2/4] PPC64-HWBKPT: Implement hw-breakpoints for PowerPC Book III S

[K.Prasad]

Implement perf-events based hw-breakpoint interfaces for PowerPC Book III S
processors. These interfaces help arbitrate requests from various users and
schedules them as appropriate.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 arch/powerpc/Kconfig                     |    1 
 arch/powerpc/include/asm/cputable.h      |    4 
 arch/powerpc/include/asm/hw_breakpoint.h |   49 ++++
 arch/powerpc/include/asm/processor.h     |    8 
 arch/powerpc/kernel/Makefile             |    1 
 arch/powerpc/kernel/hw_breakpoint.c      |  345 +++++++++++++++++++++++++++++++
 arch/powerpc/kernel/machine_kexec_64.c   |    3 
 arch/powerpc/kernel/process.c            |    6 
 arch/powerpc/kernel/ptrace.c             |   64 +++++
 arch/powerpc/lib/Makefile                |    1 
 include/linux/hw_breakpoint.h            |    1 
 11 files changed, 483 insertions(+)

Index: linux-2.6.ppc64_test/arch/powerpc/include/asm/hw_breakpoint.h
===================================================================
--- /dev/null
+++ linux-2.6.ppc64_test/arch/powerpc/include/asm/hw_breakpoint.h
@@ -0,0 +1,49 @@
+#ifndef _PPC_BOOK3S_64_HW_BREAKPOINT_H
+#define _PPC_BOOK3S_64_HW_BREAKPOINT_H
+
+#ifdef	__KERNEL__
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+
+struct arch_hw_breakpoint {
+	u8		len; /* length of the target data symbol */
+	int		type;
+	unsigned long	address;
+};
+
+#include <linux/kdebug.h>
+#include <asm/reg.h>
+#include <asm/system.h>
+
+static inline int hw_breakpoint_slots(int type)
+{
+	return HBP_NUM;
+}
+struct perf_event;
+struct pmu;
+struct perf_sample_data;
+
+#define HW_BREAKPOINT_ALIGN 0x7
+/* Maximum permissible length of any HW Breakpoint */
+#define HW_BREAKPOINT_LEN 0x8
+
+extern int arch_bp_generic_fields(int type, int *gen_bp_type);
+extern int arch_check_bp_in_kernelspace(struct perf_event *bp);
+extern int arch_validate_hwbkpt_settings(struct perf_event *bp);
+extern int hw_breakpoint_exceptions_notify(struct notifier_block *unused,
+						unsigned long val, void *data);
+int arch_install_hw_breakpoint(struct perf_event *bp);
+void arch_uninstall_hw_breakpoint(struct perf_event *bp);
+void hw_breakpoint_pmu_read(struct perf_event *bp);
+extern void flush_ptrace_hw_breakpoint(struct task_struct *tsk);
+
+extern struct pmu perf_ops_bp;
+extern void ptrace_triggered(struct perf_event *bp, int nmi,
+			struct perf_sample_data *data, struct pt_regs *regs);
+static inline void hw_breakpoint_disable(void)
+{
+	set_dabr(0);
+}
+
+#endif	/* CONFIG_HAVE_HW_BREAKPOINT */
+#endif	/* __KERNEL__ */
+#endif	/* _PPC_BOOK3S_64_HW_BREAKPOINT_H */
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c
===================================================================
--- /dev/null
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c
@@ -0,0 +1,345 @@
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers. Derived from
+ * "arch/x86/kernel/hw_breakpoint.c"
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright 2010 IBM Corporation
+ * Author: K.Prasad <prasad@linux.vnet.ibm.com>
+ *
+ */
+
+#include <linux/hw_breakpoint.h>
+#include <linux/notifier.h>
+#include <linux/kprobes.h>
+#include <linux/percpu.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/smp.h>
+
+#include <asm/hw_breakpoint.h>
+#include <asm/processor.h>
+#include <asm/sstep.h>
+
+/*
+ * Stores the breakpoints currently in use on each breakpoint address
+ * register for every cpu
+ */
+static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
+
+/*
+ * Install a perf counter breakpoint.
+ *
+ * We seek a free debug address register and use it for this
+ * breakpoint.
+ *
+ * Atomic: we hold the counter->ctx->lock and we only handle variables
+ * and registers local to this cpu.
+ */
+int arch_install_hw_breakpoint(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+	struct perf_event **slot = &__get_cpu_var(bp_per_reg);
+
+	*slot = bp;
+
+	/*
+	 * Do not install DABR values if the instruction must be single-stepped.
+	 * If so, DABR will be populated in single_step_dabr_instruction().
+	 */
+	if (current->thread.last_hit_ubp != bp)
+		set_dabr(info->address | info->type | DABR_TRANSLATION);
+
+	return 0;
+}
+
+/*
+ * Uninstall the breakpoint contained in the given counter.
+ *
+ * First we search the debug address register it uses and then we disable
+ * it.
+ *
+ * Atomic: we hold the counter->ctx->lock and we only handle variables
+ * and registers local to this cpu.
+ */
+void arch_uninstall_hw_breakpoint(struct perf_event *bp)
+{
+	struct perf_event **slot = &__get_cpu_var(bp_per_reg);
+
+	if (*slot != bp) {
+		WARN_ONCE(1, "Can't find the breakpoint");
+		return;
+	}
+
+	*slot = NULL;
+	set_dabr(0);
+}
+
+/*
+ * Perform cleanup of arch-specific counters during unregistration
+ * of the perf-event
+ */
+void arch_unregister_hw_breakpoint(struct perf_event *bp)
+{
+	/*
+	 * If the breakpoint is unregistered between a hw_breakpoint_handler()
+	 * and the single_step_dabr_instruction(), then cleanup the breakpoint
+	 * restoration variables to prevent dangling pointers.
+	 */
+	if (bp->ctx->task)
+		bp->ctx->task->thread.last_hit_ubp = NULL;
+
+	put_cpu();
+}
+
+/*
+ * Check for virtual address in kernel space.
+ */
+int arch_check_bp_in_kernelspace(struct perf_event *bp)
+{
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	return is_kernel_addr(info->address);
+}
+
+int arch_bp_generic_fields(int type, int *gen_bp_type)
+{
+	switch (type) {
+	case DABR_DATA_READ:
+		*gen_bp_type = HW_BREAKPOINT_R;
+		break;
+	case DABR_DATA_WRITE:
+		*gen_bp_type = HW_BREAKPOINT_W;
+		break;
+	case (DABR_DATA_WRITE | DABR_DATA_READ):
+		*gen_bp_type = (HW_BREAKPOINT_W | HW_BREAKPOINT_R);
+		break;
+	default:
+		return -EINVAL;
+	}
+	return 0;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings
+ */
+int arch_validate_hwbkpt_settings(struct perf_event *bp)
+{
+	int ret = -EINVAL;
+	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
+
+	if (!bp)
+		return ret;
+
+	switch (bp->attr.bp_type) {
+	case HW_BREAKPOINT_R:
+		info->type = DABR_DATA_READ;
+		break;
+	case HW_BREAKPOINT_W:
+		info->type = DABR_DATA_WRITE;
+		break;
+	case HW_BREAKPOINT_R | HW_BREAKPOINT_W:
+		info->type = (DABR_DATA_READ | DABR_DATA_WRITE);
+		break;
+	default:
+		return ret;
+	}
+
+	info->address = bp->attr.bp_addr;
+	info->len = bp->attr.bp_len;
+
+	/*
+	 * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
+	 * and breakpoint addresses are aligned to nearest double-word
+	 * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
+	 * 'symbolsize' should satisfy the check below.
+	 */
+	if (info->len >
+	    (HW_BREAKPOINT_LEN - (info->address & HW_BREAKPOINT_ALIGN)))
+		return -EINVAL;
+	return 0;
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+int __kprobes hw_breakpoint_handler(struct die_args *args)
+{
+	bool is_kernel, is_ptrace_bp = false;
+	int rc = NOTIFY_STOP;
+	struct perf_event *bp;
+	struct pt_regs *regs = args->regs;
+	unsigned long dar = regs->dar;
+	int stepped = 1;
+	struct arch_hw_breakpoint *info;
+
+	/* Disable breakpoints during exception handling */
+	set_dabr(0);
+	/*
+	 * The counter may be concurrently released but that can only
+	 * occur from a call_rcu() path. We can then safely fetch
+	 * the breakpoint, use its callback, touch its counter
+	 * while we are in an rcu_read_lock() path.
+	 */
+	rcu_read_lock();
+
+	bp = __get_cpu_var(bp_per_reg);
+	if (!bp)
+		goto out;
+	info = counter_arch_bp(bp);
+	is_kernel = is_kernel_addr(bp->attr.bp_addr);
+	is_ptrace_bp = (bp->overflow_handler == ptrace_triggered) ?
+			true : false;
+
+	/*
+	 * Verify if dar lies within the address range occupied by the symbol
+	 * being watched to filter extraneous exceptions.
+	 */
+	if (!((bp->attr.bp_addr <= dar) &&
+	    (dar <= (bp->attr.bp_addr + bp->attr.bp_len))) &&
+	    (!is_ptrace_bp))
+		/*
+		 * This exception is triggered not because of a memory access on
+		 * the monitored variable but in the double-word address range
+		 * in which it is contained. We will consume this exception,
+		 * considering it as 'noise'.
+		 */
+		goto restore_bp;
+
+	/*
+	 * Return early after invoking user-callback function without restoring
+	 * DABR if the breakpoint is from ptrace which always operates in
+	 * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
+	 * generated in do_dabr().
+	 */
+	if (is_ptrace_bp) {
+		perf_bp_event(bp, regs);
+		rc = NOTIFY_DONE;
+		goto out;
+	}
+
+	/*
+	 * Do not emulate user-space instructions from kernel-space,
+	 * instead single-step them.
+	 */
+	if (!is_kernel) {
+		bp->ctx->task->thread.last_hit_ubp = bp;
+		regs->msr |= MSR_SE;
+		goto out;
+	}
+
+	stepped = emulate_step(regs, regs->nip);
+	/*
+	 * emulate_step() could not execute it. We've failed in reliably
+	 * handling the hw-breakpoint. Unregister it and throw a warning
+	 * message to let the user know about it.
+	 */
+	if (stepped == 0) {
+		WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
+			"0x%lx will be uninstalled.", info->address);
+		unregister_hw_breakpoint(bp);
+		goto out;
+	}
+	/*
+	 * As a policy, the callback is invoked in a 'trigger-after-execute'
+	 * fashion
+	 */
+	perf_bp_event(bp, regs);
+
+restore_bp:
+	set_dabr(info->address | info->type | DABR_TRANSLATION);
+out:
+	rcu_read_unlock();
+	return rc;
+}
+
+/*
+ * Handle single-step exceptions following a DABR hit.
+ */
+int __kprobes single_step_dabr_instruction(struct die_args *args)
+{
+	struct pt_regs *regs = args->regs;
+	struct perf_event *bp = NULL;
+	struct arch_hw_breakpoint *bp_info;
+
+	bp = current->thread.last_hit_ubp;
+	/*
+	 * Check if we are single-stepping as a result of a
+	 * previous HW Breakpoint exception
+	 */
+	if (!bp)
+		return NOTIFY_DONE;
+
+	bp_info = counter_arch_bp(bp);
+
+	/*
+	 * We shall invoke the user-defined callback function in the single
+	 * stepping handler to confirm to 'trigger-after-execute' semantics
+	 */
+	perf_bp_event(bp, regs);
+
+	/*
+	 * Do not disable MSR_SE if the process was already in
+	 * single-stepping mode. We cannot reliable detect single-step mode
+	 * for kernel-space breakpoints, so this cannot work along with other
+	 * debuggers (like KGDB, xmon) which may be single-stepping kernel code.
+	 */
+	if (!(!is_kernel_addr(bp->attr.bp_addr) &&
+	     test_thread_flag(TIF_SINGLESTEP)))
+		regs->msr &= ~MSR_SE;
+
+	set_dabr(bp_info->address | bp_info->type | DABR_TRANSLATION);
+	return NOTIFY_STOP;
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+int __kprobes hw_breakpoint_exceptions_notify(
+		struct notifier_block *unused, unsigned long val, void *data)
+{
+	int ret = NOTIFY_DONE;
+
+	switch (val) {
+	case DIE_DABR_MATCH:
+		ret = hw_breakpoint_handler(data);
+		break;
+	case DIE_SSTEP:
+		ret = single_step_dabr_instruction(data);
+		break;
+	}
+
+	return ret;
+}
+
+/*
+ * Release the user breakpoints used by ptrace
+ */
+void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
+{
+	struct thread_struct *t = &tsk->thread;
+
+	unregister_hw_breakpoint(t->ptrace_bps[0]);
+	t->ptrace_bps[0] = NULL;
+}
+
+void hw_breakpoint_pmu_read(struct perf_event *bp)
+{
+	/* TODO */
+}
+
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/Makefile
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/Makefile
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/Makefile
@@ -34,6 +34,7 @@ obj-y				+= vdso32/
 obj-$(CONFIG_PPC64)		+= setup_64.o sys_ppc32.o \
 				   signal_64.o ptrace32.o \
 				   paca.o nvram_64.o firmware.o
+obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
 obj-$(CONFIG_PPC_BOOK3S_64)	+= cpu_setup_ppc970.o cpu_setup_pa6t.o
 obj64-$(CONFIG_RELOCATABLE)	+= reloc_64.o
 obj-$(CONFIG_PPC_BOOK3E_64)	+= exceptions-64e.o
Index: linux-2.6.ppc64_test/arch/powerpc/include/asm/processor.h
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/include/asm/processor.h
+++ linux-2.6.ppc64_test/arch/powerpc/include/asm/processor.h
@@ -209,6 +209,14 @@ struct thread_struct {
 #ifdef CONFIG_PPC64
 	unsigned long	start_tb;	/* Start purr when proc switched in */
 	unsigned long	accum_tb;	/* Total accumilated purr for process */
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	struct perf_event *ptrace_bps[HBP_NUM];
+	/*
+	 * Helps identify source of single-step exception and subsequent
+	 * hw-breakpoint enablement
+	 */
+	struct perf_event *last_hit_ubp;
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 #endif
 	unsigned long	dabr;		/* Data address breakpoint register */
 #ifdef CONFIG_ALTIVEC
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/ptrace.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/ptrace.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/ptrace.c
@@ -32,6 +32,8 @@
 #ifdef CONFIG_PPC32
 #include <linux/module.h>
 #endif
+#include <linux/hw_breakpoint.h>
+#include <linux/perf_event.h>
 
 #include <asm/uaccess.h>
 #include <asm/page.h>
@@ -866,9 +868,34 @@ void user_disable_single_step(struct tas
 	clear_tsk_thread_flag(task, TIF_SINGLESTEP);
 }
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+void ptrace_triggered(struct perf_event *bp, int nmi,
+		      struct perf_sample_data *data, struct pt_regs *regs)
+{
+	struct perf_event_attr attr;
+
+	/*
+	 * Disable the breakpoint request here since ptrace has defined a
+	 * one-shot behaviour for breakpoint exceptions in PPC64.
+	 * The SIGTRAP signal is generated automatically for us in do_dabr().
+	 * We don't have to do anything about that here
+	 */
+	attr = bp->attr;
+	attr.disabled = true;
+	modify_user_hw_breakpoint(bp, &attr);
+}
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
+
 int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
 			       unsigned long data)
 {
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	int ret;
+	struct thread_struct *thread = &(task->thread);
+	struct perf_event *bp;
+	struct perf_event_attr attr;
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
+
 	/* For ppc64 we support one DABR and no IABR's at the moment (ppc64).
 	 *  For embedded processors we support one DAC and no IAC's at the
 	 *  moment.
@@ -896,6 +923,43 @@ int ptrace_set_debugreg(struct task_stru
 	/* Ensure breakpoint translation bit is set */
 	if (data && !(data & DABR_TRANSLATION))
 		return -EIO;
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	bp = thread->ptrace_bps[0];
+	if ((!data) || !(data & (DABR_DATA_WRITE | DABR_DATA_READ))) {
+		if (bp) {
+			unregister_hw_breakpoint(bp);
+			thread->ptrace_bps[0] = NULL;
+		}
+		return 0;
+	}
+	if (bp) {
+		attr = bp->attr;
+		attr.bp_addr = data & ~HW_BREAKPOINT_ALIGN;
+		arch_bp_generic_fields(data &
+					(DABR_DATA_WRITE | DABR_DATA_READ),
+							&attr.bp_type);
+		ret =  modify_user_hw_breakpoint(bp, &attr);
+		if (ret)
+			return ret;
+		thread->ptrace_bps[0] = bp;
+		thread->dabr = data;
+		return 0;
+	}
+
+	/* Create a new breakpoint request if one doesn't exist already */
+	hw_breakpoint_init(&attr);
+	attr.bp_addr = data & ~HW_BREAKPOINT_ALIGN;
+	arch_bp_generic_fields(data & (DABR_DATA_WRITE | DABR_DATA_READ),
+								&attr.bp_type);
+
+	thread->ptrace_bps[0] = bp = register_user_hw_breakpoint(&attr,
+							ptrace_triggered, task);
+	if (IS_ERR(bp)) {
+		thread->ptrace_bps[0] = NULL;
+		return PTR_ERR(bp);
+	}
+
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 
 	/* Move contents to the DABR register */
 	task->thread.dabr = data;
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/process.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/process.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/process.c
@@ -462,8 +462,14 @@ struct task_struct *__switch_to(struct t
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
 	switch_booke_debug_regs(&new->thread);
 #else
+/*
+ * For PPC_BOOK3S_64, we use the hw-breakpoint interfaces that would
+ * schedule DABR
+ */
+#ifndef CONFIG_HAVE_HW_BREAKPOINT
 	if (unlikely(__get_cpu_var(current_dabr) != new->thread.dabr))
 		set_dabr(new->thread.dabr);
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 #endif
 
 
Index: linux-2.6.ppc64_test/arch/powerpc/include/asm/cputable.h
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/include/asm/cputable.h
+++ linux-2.6.ppc64_test/arch/powerpc/include/asm/cputable.h
@@ -516,6 +516,10 @@ static inline int cpu_has_feature(unsign
 		& feature);
 }
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+#define HBP_NUM 1
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __KERNEL__ */
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/machine_kexec_64.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/machine_kexec_64.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/machine_kexec_64.c
@@ -15,6 +15,7 @@
 #include <linux/thread_info.h>
 #include <linux/init_task.h>
 #include <linux/errno.h>
+#include <linux/hw_breakpoint.h>
 
 #include <asm/page.h>
 #include <asm/current.h>
@@ -165,6 +166,7 @@ static void kexec_smp_down(void *arg)
 	while(kexec_all_irq_disabled == 0)
 		cpu_relax();
 	mb(); /* make sure all irqs are disabled before this */
+	hw_breakpoint_disable();
 	/*
 	 * Now every CPU has IRQs off, we can clear out any pending
 	 * IPIs and be sure that no more will come in after this.
@@ -180,6 +182,7 @@ static void kexec_prepare_cpus_wait(int 
 {
 	int my_cpu, i, notified=-1;
 
+	hw_breakpoint_disable();
 	my_cpu = get_cpu();
 	/* Make sure each CPU has atleast made it to the state we need */
 	for (i=0; i < NR_CPUS; i++) {
Index: linux-2.6.ppc64_test/arch/powerpc/lib/Makefile
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/lib/Makefile
+++ linux-2.6.ppc64_test/arch/powerpc/lib/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_PPC64)	+= copypage_64.o cop
 			   memcpy_64.o usercopy_64.o mem_64.o string.o
 obj-$(CONFIG_XMON)	+= sstep.o
 obj-$(CONFIG_KPROBES)	+= sstep.o
+obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= sstep.o
 
 ifeq ($(CONFIG_PPC64),y)
 obj-$(CONFIG_SMP)	+= locks.o
Index: linux-2.6.ppc64_test/include/linux/hw_breakpoint.h
===================================================================
--- linux-2.6.ppc64_test.orig/include/linux/hw_breakpoint.h
+++ linux-2.6.ppc64_test/include/linux/hw_breakpoint.h
@@ -139,6 +139,7 @@ static inline struct arch_hw_breakpoint 
 {
 	return NULL;
 }
+static inline void hw_breakpoint_disable(void) { }
 
 #endif /* CONFIG_HAVE_HW_BREAKPOINT */
 #endif /* __KERNEL__ */
Index: linux-2.6.ppc64_test/arch/powerpc/Kconfig
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/Kconfig
+++ linux-2.6.ppc64_test/arch/powerpc/Kconfig
@@ -141,6 +141,7 @@ config PPC
 	select GENERIC_ATOMIC64 if PPC32
 	select HAVE_PERF_EVENTS
 	select HAVE_REGS_AND_STACK_ACCESS_API
+	select HAVE_HW_BREAKPOINT if PERF_EVENTS && PPC_BOOK3S_64
 
 config EARLY_PRINTK
 	bool

[Patch 3/4] PPC64-HWBKPT: Handle concurrent alignment interrupts

[K.Prasad]

An alignment interrupt may intervene between a DSI/hw-breakpoint exception
and the single-step exception. Enable the alignment interrupt (through
modifications to emulate_single_step()) to notify the single-step exception
handler for proper restoration of hw-breakpoints.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/traps.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

Index: linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/traps.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
@@ -602,7 +602,7 @@ void RunModeException(struct pt_regs *re
 
 void __kprobes single_step_exception(struct pt_regs *regs)
 {
-	regs->msr &= ~(MSR_SE | MSR_BE);  /* Turn off 'trace' bits */
+	clear_single_step(regs);
 
 	if (notify_die(DIE_SSTEP, "single_step", regs, 5,
 					5, SIGTRAP) == NOTIFY_STOP)
@@ -621,10 +621,7 @@ void __kprobes single_step_exception(str
  */
 static void emulate_single_step(struct pt_regs *regs)
 {
-	if (single_stepping(regs)) {
-		clear_single_step(regs);
-		_exception(SIGTRAP, regs, TRAP_TRACE, 0);
-	}
+	single_step_exception(regs);
 }
 
 static inline int __parse_fpscr(unsigned long fpscr)

[Patch 4/4] PPC64-HWBKPT: Enable hw-breakpoints while handling intervening signals

[K.Prasad]

A signal delivered between a hw_breakpoint_handler() and the
single_step_dabr_instruction() will not have the breakpoint active during
signal handling (since breakpoint will not be restored through single-stepping
due to absence of MSR_SE bit on the signal frame). Enable breakpoints before
signal delivery and clear them during sigreturn() syscall.

Limitation: Nested hw-breakpoint exceptions (where second exception is raised
inside signal context) will cause a 'double-hit' i.e. the first breakpoint
exception will be taken twice.

Restore hw-breakpoints if the user-context is altered in the signal handler
(causing loss of MSR_SE). Side-effect: 'Double-hit' of breakpoint if the
instruction pointer is unaltered in the new context.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/hw_breakpoint.h |    3 +++
 arch/powerpc/kernel/hw_breakpoint.c      |   28 ++++++++++++++++++++++++++++
 arch/powerpc/kernel/signal.c             |    8 ++++++++
 arch/powerpc/kernel/signal_32.c          |   10 ++++++++++
 arch/powerpc/kernel/signal_64.c          |    7 +++++++
 5 files changed, 56 insertions(+)

Index: linux-2.6.ppc64_test/arch/powerpc/include/asm/hw_breakpoint.h
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/include/asm/hw_breakpoint.h
+++ linux-2.6.ppc64_test/arch/powerpc/include/asm/hw_breakpoint.h
@@ -43,6 +43,9 @@ static inline void hw_breakpoint_disable
 {
 	set_dabr(0);
 }
+extern void sighandler_install_bp(struct task_struct *tsk);
+extern void sigreturn_uninstall_bp(struct task_struct *tsk);
+extern void thread_change_pc(struct task_struct *tsk, unsigned long msr);
 
 #endif	/* CONFIG_HAVE_HW_BREAKPOINT */
 #endif	/* __KERNEL__ */
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/hw_breakpoint.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/hw_breakpoint.c
@@ -175,6 +175,34 @@ int arch_validate_hwbkpt_settings(struct
 	return 0;
 }
 
+void sighandler_install_bp(struct task_struct *tsk)
+{
+	struct arch_hw_breakpoint *info;
+
+	if (likely(!tsk->thread.last_hit_ubp))
+		return;
+
+	info = counter_arch_bp(tsk->thread.last_hit_ubp);
+	set_dabr(info->address | info->type | DABR_TRANSLATION);
+}
+
+void sigreturn_uninstall_bp(struct task_struct *tsk)
+{
+	if (unlikely(tsk->thread.last_hit_ubp))
+		set_dabr(0);
+}
+
+void thread_change_pc(struct task_struct *tsk, unsigned long new_msr)
+{
+	/*
+	 * Do not bother to restore breakpoints if single-stepping is not
+	 * cleared. single_step_dabr_instruction() will handle it if MSR_SE
+	 * is set.
+	 */
+	if (!(new_msr & MSR_SE))
+		sighandler_install_bp(tsk);
+}
+
 /*
  * Handle debug exception notifications.
  */
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/signal.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/signal.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/signal.c
@@ -11,6 +11,7 @@
 
 #include <linux/tracehook.h>
 #include <linux/signal.h>
+#include <asm/hw_breakpoint.h>
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
 
@@ -149,6 +150,13 @@ static int do_signal_pending(sigset_t *o
 	if (current->thread.dabr)
 		set_dabr(current->thread.dabr);
 #endif
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	/*
+	 * Re-enable the breakpoints (if it was previously cleared in
+	 * hw_breakpoint_handler()) for the signal stack.
+	 */
+	sighandler_install_bp(current);
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 
 	if (is32) {
         	if (ka.sa.sa_flags & SA_SIGINFO)
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/signal_64.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/signal_64.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/signal_64.c
@@ -33,6 +33,7 @@
 #include <asm/cacheflush.h>
 #include <asm/syscalls.h>
 #include <asm/vdso.h>
+#include <asm/hw_breakpoint.h>
 
 #include "signal.h"
 
@@ -312,6 +313,9 @@ int sys_swapcontext(struct ucontext __us
 		    || __copy_to_user(&old_ctx->uc_sigmask,
 				      &current->blocked, sizeof(sigset_t)))
 			return -EFAULT;
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+		thread_change_pc(current, new_msr);
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 	}
 	if (new_ctx == NULL)
 		return 0;
@@ -364,6 +368,9 @@ int sys_rt_sigreturn(unsigned long r3, u
 	if (__copy_from_user(&set, &uc->uc_sigmask, sizeof(set)))
 		goto badframe;
 	restore_sigmask(&set);
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	sigreturn_uninstall_bp(current);
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 	if (restore_sigcontext(regs, NULL, 1, &uc->uc_mcontext))
 		goto badframe;
 
Index: linux-2.6.ppc64_test/arch/powerpc/kernel/signal_32.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/signal_32.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/signal_32.c
@@ -42,6 +42,7 @@
 #include <asm/syscalls.h>
 #include <asm/sigcontext.h>
 #include <asm/vdso.h>
+#include <asm/hw_breakpoint.h>
 #ifdef CONFIG_PPC64
 #include "ppc32.h"
 #include <asm/unistd.h>
@@ -996,6 +997,9 @@ long sys_swapcontext(struct ucontext __u
 		    || put_sigset_t(&old_ctx->uc_sigmask, &current->blocked)
 		    || __put_user(to_user_ptr(mctx), &old_ctx->uc_regs))
 			return -EFAULT;
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+		thread_change_pc(current, new_msr);
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 	}
 	if (new_ctx == NULL)
 		return 0;
@@ -1034,6 +1038,9 @@ long sys_rt_sigreturn(int r3, int r4, in
 		(regs->gpr[1] + __SIGNAL_FRAMESIZE + 16);
 	if (!access_ok(VERIFY_READ, rt_sf, sizeof(*rt_sf)))
 		goto bad;
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	sigreturn_uninstall_bp(current);
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 	if (do_setcontext(&rt_sf->uc, regs, 1))
 		goto bad;
 
@@ -1279,6 +1286,9 @@ long sys_sigreturn(int r3, int r4, int r
 #endif
 	restore_sigmask(&set);
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	sigreturn_uninstall_bp(current);
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 	sr = (struct mcontext __user *)from_user_ptr(sigctx.regs);
 	addr = sr;
 	if (!access_ok(VERIFY_READ, sr, sizeof(*sr))

Re: [Patch 4/4] PPC64-HWBKPT: Enable hw-breakpoints while handling intervening signals

[Paul Mackerras]

On Mon, May 24, 2010 at 04:04:19PM +0530, K.Prasad wrote:

> A signal delivered between a hw_breakpoint_handler() and the
> single_step_dabr_instruction() will not have the breakpoint active during
> signal handling (since breakpoint will not be restored through single-stepping
> due to absence of MSR_SE bit on the signal frame). Enable breakpoints before
> signal delivery and clear them during sigreturn() syscall.
> 
> Limitation: Nested hw-breakpoint exceptions (where second exception is raised
> inside signal context) will cause a 'double-hit' i.e. the first breakpoint
> exception will be taken twice.

I don't think this will actually cause a problem.  In the case of a
perf_event breakpoint, the semantics are trigger-after-execute, so the
first hit won't cause a trigger, and perf_event won't double-count it.
In the case of ptrace-style breakpoints, we don't single-step (it's up
to the ptracer to do the single-stepping if needed) so the problem
doesn't arise.

In fact I don't think we even need to do anything on sigreturn.  Yes,
we are changing the NIP but we are changing it to a previous value as
a result of an explicit action by the program, which is a bit
different to what signal delivery and ptrace do.

On signal delivery I was imagining that we would clear the MSR_SE bit
before saving the MSR value in the signal frame, and reinstall the
DABR value at the same time, and then essentially forget that we had
already hit the breakpoint once and just wait for it to hit again.

Paul.

[Patch 3/4] PPC64-HWBKPT: Handle concurrent alignment interrupts

[K.Prasad]

An alignment interrupt may intervene between a DSI/hw-breakpoint exception
and the single-step exception. Enable the alignment interrupt (through
modifications to emulate_single_step()) to notify the single-step exception
handler for proper restoration of hw-breakpoints.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/traps.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

Index: linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
===================================================================
--- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/traps.c
+++ linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
@@ -602,7 +602,7 @@ void RunModeException(struct pt_regs *re
 
 void __kprobes single_step_exception(struct pt_regs *regs)
 {
-	regs->msr &= ~(MSR_SE | MSR_BE);  /* Turn off 'trace' bits */
+	clear_single_step(regs);
 
 	if (notify_die(DIE_SSTEP, "single_step", regs, 5,
 					5, SIGTRAP) == NOTIFY_STOP)
@@ -621,10 +621,7 @@ void __kprobes single_step_exception(str
  */
 static void emulate_single_step(struct pt_regs *regs)
 {
-	if (single_stepping(regs)) {
-		clear_single_step(regs);
-		_exception(SIGTRAP, regs, TRAP_TRACE, 0);
-	}
+	single_step_exception(regs);
 }
 
 static inline int __parse_fpscr(unsigned long fpscr)

Re: [Patch 3/4] PPC64-HWBKPT: Handle concurrent alignment interrupts

[Paul Mackerras]

On Tue, May 25, 2010 at 02:44:35PM +0530, K.Prasad wrote:

> An alignment interrupt may intervene between a DSI/hw-breakpoint exception
> and the single-step exception. Enable the alignment interrupt (through
> modifications to emulate_single_step()) to notify the single-step exception
> handler for proper restoration of hw-breakpoints.
> 
> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> ---
>  arch/powerpc/kernel/traps.c |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> Index: linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
> ===================================================================
> --- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/traps.c
> +++ linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
> @@ -602,7 +602,7 @@ void RunModeException(struct pt_regs *re
>  
>  void __kprobes single_step_exception(struct pt_regs *regs)
>  {
> -	regs->msr &= ~(MSR_SE | MSR_BE);  /* Turn off 'trace' bits */
> +	clear_single_step(regs);
>  
>  	if (notify_die(DIE_SSTEP, "single_step", regs, 5,
>  					5, SIGTRAP) == NOTIFY_STOP)
> @@ -621,10 +621,7 @@ void __kprobes single_step_exception(str
>   */
>  static void emulate_single_step(struct pt_regs *regs)
>  {
> -	if (single_stepping(regs)) {
> -		clear_single_step(regs);
> -		_exception(SIGTRAP, regs, TRAP_TRACE, 0);
> -	}
> +	single_step_exception(regs);
>  }

We still need the if (single_stepping(regs)) in emulate_single_step.
We don't want to send the process a SIGTRAP every time it gets an
alignment interrupt. :)

Paul.

Re: [Patch 3/4] PPC64-HWBKPT: Handle concurrent alignment interrupts

[K.Prasad]

On Thu, May 27, 2010 at 04:20:44PM +1000, Paul Mackerras wrote:
> On Tue, May 25, 2010 at 02:44:35PM +0530, K.Prasad wrote:
> 
> > An alignment interrupt may intervene between a DSI/hw-breakpoint exception
> > and the single-step exception. Enable the alignment interrupt (through
> > modifications to emulate_single_step()) to notify the single-step exception
> > handler for proper restoration of hw-breakpoints.
> > 
> > Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> > ---
> >  arch/powerpc/kernel/traps.c |    7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> > 
> > Index: linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
> > ===================================================================
> > --- linux-2.6.ppc64_test.orig/arch/powerpc/kernel/traps.c
> > +++ linux-2.6.ppc64_test/arch/powerpc/kernel/traps.c
> > @@ -602,7 +602,7 @@ void RunModeException(struct pt_regs *re
> >  
> >  void __kprobes single_step_exception(struct pt_regs *regs)
> >  {
> > -	regs->msr &= ~(MSR_SE | MSR_BE);  /* Turn off 'trace' bits */
> > +	clear_single_step(regs);
> >  
> >  	if (notify_die(DIE_SSTEP, "single_step", regs, 5,
> >  					5, SIGTRAP) == NOTIFY_STOP)
> > @@ -621,10 +621,7 @@ void __kprobes single_step_exception(str
> >   */
> >  static void emulate_single_step(struct pt_regs *regs)
> >  {
> > -	if (single_stepping(regs)) {
> > -		clear_single_step(regs);
> > -		_exception(SIGTRAP, regs, TRAP_TRACE, 0);
> > -	}
> > +	single_step_exception(regs);
> >  }
> 
> We still need the if (single_stepping(regs)) in emulate_single_step.
> We don't want to send the process a SIGTRAP every time it gets an
> alignment interrupt. :)
> 
> Paul.

Agreed, and made changes to that effect in version XXII (as seen in
patch linuxppc-dev message-id: 20100528064017.GD8679@in.ibm.com).

Thanks,
K.Prasad