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Subject[Patch 02/12] Introducing generic hardware breakpoint handler interfaces
This patch introduces the generic Hardware Breakpoint interfaces for both user
and kernel space requests.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
arch/Kconfig | 4
kernel/Makefile | 1
kernel/hw_breakpoint.c | 369 +++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 374 insertions(+)
Index: arch/Kconfig
===================================================================
--- arch/Kconfig.orig
+++ arch/Kconfig
@@ -112,3 +112,7 @@ config HAVE_DMA_API_DEBUG

config HAVE_DEFAULT_NO_SPIN_MUTEXES
bool
+
+config HAVE_HW_BREAKPOINT
+ bool
+
Index: kernel/Makefile
===================================================================
--- kernel/Makefile.orig
+++ kernel/Makefile
@@ -97,6 +97,7 @@ obj-$(CONFIG_X86_DS) += trace/
obj-$(CONFIG_SMP) += sched_cpupri.o
obj-$(CONFIG_SLOW_WORK) += slow-work.o
obj-$(CONFIG_PERF_COUNTERS) += perf_counter.o
+obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o

ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
# According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
Index: kernel/hw_breakpoint.c
===================================================================
--- /dev/null
+++ kernel/hw_breakpoint.c
@@ -0,0 +1,369 @@
+/*
+ * 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 (C) 2007 Alan Stern
+ * Copyright (C) IBM Corporation, 2009
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ * This file contains the arch-independent routines.
+ */
+
+#include <linux/irqflags.h>
+#include <linux/kallsyms.h>
+#include <linux/notifier.h>
+#include <linux/kprobes.h>
+#include <linux/kdebug.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/smp.h>
+
+#include <asm/hw_breakpoint.h>
+#include <asm/processor.h>
+
+#ifdef CONFIG_X86
+#include <asm/debugreg.h>
+#endif
+/*
+ * Spinlock that protects all (un)register operations over kernel/user-space
+ * breakpoint requests
+ */
+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.
+ */
+DEFINE_PER_CPU(struct hw_breakpoint*, this_hbp_kernel[HBP_NUM]);
+
+/*
+ * Kernel breakpoints grow downwards, starting from HBP_NUM
+ * 'hbp_kernel_pos' denotes lowest numbered breakpoint register occupied for
+ * kernel-space request. We will initialise it here and not in an __init
+ * routine because load_debug_registers(), which uses this variable can be
+ * called very early during CPU initialisation.
+ */
+unsigned int hbp_kernel_pos = HBP_NUM;
+
+/*
+ * An array containing refcount of threads using a given bkpt register
+ * Accesses are synchronised by acquiring hw_breakpoint_lock
+ */
+unsigned int hbp_user_refcount[HBP_NUM];
+
+/*
+ * Load the debug registers during startup of a CPU.
+ */
+void load_debug_registers(void)
+{
+ 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);
+
+ spin_unlock_bh(&hw_breakpoint_lock);
+}
+
+/*
+ * Erase all the hardware breakpoint info associated with a thread.
+ *
+ * If tsk != current then tsk must not be usable (for example, a
+ * child being cleaned up from a failed fork).
+ */
+void flush_thread_hw_breakpoint(struct task_struct *tsk)
+{
+ int i;
+ struct thread_struct *thread = &(tsk->thread);
+
+ spin_lock_bh(&hw_breakpoint_lock);
+
+ /* The thread no longer has any breakpoints associated with it */
+ clear_tsk_thread_flag(tsk, TIF_DEBUG);
+ for (i = 0; i < HBP_NUM; i++) {
+ if (thread->hbp[i]) {
+ hbp_user_refcount[i]--;
+ kfree(thread->hbp[i]);
+ thread->hbp[i] = NULL;
+ }
+ }
+
+ arch_flush_thread_hw_breakpoint(tsk);
+
+ /* Actually uninstall the breakpoints if necessary */
+ if (tsk == current)
+ arch_uninstall_thread_hw_breakpoint();
+ spin_unlock_bh(&hw_breakpoint_lock);
+}
+
+/*
+ * Copy the hardware breakpoint info from a thread to its cloned child.
+ */
+int copy_thread_hw_breakpoint(struct task_struct *tsk,
+ struct task_struct *child, unsigned long clone_flags)
+{
+ /*
+ * We will assume that breakpoint settings are not inherited
+ * and the child starts out with no debug registers set.
+ * But what about CLONE_PTRACE?
+ */
+ clear_tsk_thread_flag(child, TIF_DEBUG);
+
+ /* We will call flush routine since the debugregs are not inherited */
+ arch_flush_thread_hw_breakpoint(child);
+
+ return 0;
+}
+
+static int __register_user_hw_breakpoint(int pos, struct task_struct *tsk,
+ struct hw_breakpoint *bp)
+{
+ struct thread_struct *thread = &(tsk->thread);
+ int rc;
+
+ /* Do not overcommit. Fail if kernel has used the hbp registers */
+ if (pos >= hbp_kernel_pos)
+ return -ENOSPC;
+
+ rc = arch_validate_hwbkpt_settings(bp, tsk);
+ if (rc)
+ return rc;
+
+ thread->hbp[pos] = bp;
+ hbp_user_refcount[pos]++;
+
+ arch_update_user_hw_breakpoint(pos, tsk);
+ /*
+ * Does it need to be installed right now?
+ * Otherwise it will get installed the next time tsk runs
+ */
+ if (tsk == current)
+ arch_install_thread_hw_breakpoint(tsk);
+
+ return rc;
+}
+
+/*
+ * Modify the address of a hbp register already in use by the task
+ * Do not invoke this in-lieu of a __unregister_user_hw_breakpoint()
+ */
+static int __modify_user_hw_breakpoint(int pos, struct task_struct *tsk,
+ struct hw_breakpoint *bp)
+{
+ struct thread_struct *thread = &(tsk->thread);
+
+ if ((pos >= hbp_kernel_pos) || (arch_validate_hwbkpt_settings(bp, tsk)))
+ return -EINVAL;
+
+ if (thread->hbp[pos] == NULL)
+ return -EINVAL;
+
+ thread->hbp[pos] = bp;
+ /*
+ * 'pos' must be that of a hbp register already used by 'tsk'
+ * Otherwise arch_modify_user_hw_breakpoint() will fail
+ */
+ arch_update_user_hw_breakpoint(pos, tsk);
+
+ if (tsk == current)
+ arch_install_thread_hw_breakpoint(tsk);
+
+ return 0;
+}
+
+static void __unregister_user_hw_breakpoint(int pos, struct task_struct *tsk)
+{
+ hbp_user_refcount[pos]--;
+ tsk->thread.hbp[pos] = NULL;
+
+ arch_update_user_hw_breakpoint(pos, tsk);
+
+ if (tsk == current)
+ arch_install_thread_hw_breakpoint(tsk);
+}
+
+/**
+ * register_user_hw_breakpoint - register a hardware breakpoint for user space
+ * @tsk: pointer to 'task_struct' of the process to which the address belongs
+ * @bp: the breakpoint structure to register
+ *
+ * @bp.info->name or @bp.info->address, @bp.info->len, @bp.info->type and
+ * @bp->triggered must be set properly before invocation
+ *
+ */
+int register_user_hw_breakpoint(struct task_struct *tsk,
+ struct hw_breakpoint *bp)
+{
+ struct thread_struct *thread = &(tsk->thread);
+ int i, rc = -ENOSPC;
+
+ spin_lock_bh(&hw_breakpoint_lock);
+
+ for (i = 0; i < hbp_kernel_pos; i++) {
+ if (!thread->hbp[i]) {
+ rc = __register_user_hw_breakpoint(i, tsk, bp);
+ break;
+ }
+ }
+
+ spin_unlock_bh(&hw_breakpoint_lock);
+ return rc;
+}
+EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
+
+/**
+ * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
+ * @tsk: pointer to 'task_struct' of the process to which the address belongs
+ * @bp: the breakpoint structure to unregister
+ *
+ */
+int modify_user_hw_breakpoint(struct task_struct *tsk, struct hw_breakpoint *bp)
+{
+ struct thread_struct *thread = &(tsk->thread);
+ int i, ret = -ENOENT;
+
+ spin_lock_bh(&hw_breakpoint_lock);
+ for (i = 0; i < hbp_kernel_pos; i++) {
+ if (bp == thread->hbp[i]) {
+ ret = __modify_user_hw_breakpoint(i, tsk, bp);
+ break;
+ }
+ }
+ spin_unlock_bh(&hw_breakpoint_lock);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
+
+/**
+ * unregister_user_hw_breakpoint - unregister a user-space hardware breakpoint
+ * @tsk: pointer to 'task_struct' of the process to which the address belongs
+ * @bp: the breakpoint structure to unregister
+ *
+ */
+void unregister_user_hw_breakpoint(struct task_struct *tsk,
+ struct hw_breakpoint *bp)
+{
+ struct thread_struct *thread = &(tsk->thread);
+ int i;
+
+ spin_lock_bh(&hw_breakpoint_lock);
+ for (i = 0; i < hbp_kernel_pos; i++) {
+ if (bp == thread->hbp[i]) {
+ __unregister_user_hw_breakpoint(i, tsk);
+ break;
+ }
+ }
+ spin_unlock_bh(&hw_breakpoint_lock);
+}
+EXPORT_SYMBOL_GPL(unregister_user_hw_breakpoint);
+
+/**
+ * register_kernel_hw_breakpoint - register a hardware breakpoint for kernel space
+ * @bp: the breakpoint structure to register
+ *
+ * @bp.info->name or @bp.info->address, @bp.info->len, @bp.info->type and
+ * @bp->triggered must be set properly before invocation
+ *
+ */
+int register_kernel_hw_breakpoint(struct hw_breakpoint *bp)
+{
+ int rc;
+
+ rc = arch_validate_hwbkpt_settings(bp, NULL);
+ if (rc)
+ return rc;
+
+ spin_lock_bh(&hw_breakpoint_lock);
+
+ rc = -EINVAL;
+ /* 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;
+ }
+
+ spin_unlock_bh(&hw_breakpoint_lock);
+ return rc;
+}
+EXPORT_SYMBOL_GPL(register_kernel_hw_breakpoint);
+
+/**
+ * unregister_kernel_hw_breakpoint - unregister a HW breakpoint for kernel space
+ * @bp: the breakpoint structure to unregister
+ *
+ * Uninstalls and unregisters @bp.
+ */
+void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp)
+{
+ int i, j;
+
+ 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;
+
+ /* 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];
+
+ hbp_kernel[hbp_kernel_pos] = NULL;
+ on_each_cpu(arch_update_kernel_hw_breakpoint, NULL, 1);
+ hbp_kernel_pos++;
+
+ spin_unlock_bh(&hw_breakpoint_lock);
+}
+EXPORT_SYMBOL_GPL(unregister_kernel_hw_breakpoint);
+
+static struct notifier_block hw_breakpoint_exceptions_nb = {
+ .notifier_call = hw_breakpoint_exceptions_notify,
+ /* we need to be notified first */
+ .priority = 0x7fffffff
+};
+
+static int __init init_hw_breakpoint(void)
+{
+ return register_die_notifier(&hw_breakpoint_exceptions_nb);
+}
+
+core_initcall(init_hw_breakpoint);


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