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Subject[Patch 3/3] HW-BKPT: Enable/disable the breakpoints when still registered
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 | 12 +++---
include/asm-generic/hw_breakpoint.h | 10 +++++
kernel/hw_breakpoint.c | 66 ++++++++++++++++++++++++++++++++++++
3 files changed, 83 insertions(+), 5 deletions(-)

Index: linux-2.6-tip.hbkpt/arch/x86/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/hw_breakpoint.c
+++ linux-2.6-tip.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 (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 (bp->enabled)
+ thread->debugreg7 |= encode_dr7(pos, bp->info.len,
+ bp->info.type);
} else
thread->debugreg[pos] = 0;
}
Index: linux-2.6-tip.hbkpt/include/asm-generic/hw_breakpoint.h
===================================================================
--- linux-2.6-tip.hbkpt.orig/include/asm-generic/hw_breakpoint.h
+++ linux-2.6-tip.hbkpt/include/asm-generic/hw_breakpoint.h
@@ -102,6 +102,12 @@
* ----------------------------------------------------------------------
*/
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.
+ */
+ bool enabled;
void (*triggered)(struct hw_breakpoint *, struct pt_regs *);
const cpumask_t *cpumask;
struct arch_hw_breakpoint info;
@@ -137,6 +143,10 @@ extern int modify_kernel_hw_breakpoint(s
struct hw_breakpoint *new_bp);
extern void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp);

+extern void enable_hw_breakpoint(struct hw_breakpoint *bp,
+ struct task_struct *tsk);
+extern void disable_hw_breakpoint(struct hw_breakpoint *bp,
+ struct task_struct *tsk);
extern unsigned int hbp_kernel_pos;

#endif /* __KERNEL__ */
Index: linux-2.6-tip.hbkpt/kernel/hw_breakpoint.c
===================================================================
--- linux-2.6-tip.hbkpt.orig/kernel/hw_breakpoint.c
+++ linux-2.6-tip.hbkpt/kernel/hw_breakpoint.c
@@ -351,6 +351,7 @@ int register_kernel_hw_breakpoint(struct
}
}

+ bp->enabled = 1;
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);
@@ -469,6 +470,71 @@ ret_path:
}
EXPORT_SYMBOL_GPL(unregister_kernel_hw_breakpoint);

+/*
+ * Worker routine that updates enabled/disabled status for kernel/user-space
+ * hw-breakpoints.
+ */
+static void update_enable_status_hbp(struct hw_breakpoint *bp,
+ struct task_struct *tsk)
+{
+ int i;
+ struct thread_struct *thread = &(tsk->thread);
+
+ spin_lock_bh(&hw_breakpoint_lock);
+
+ /* Enable/Disable the kernel-space breakpoint */
+ if (!tsk) {
+ if (cpumask_test_cpu(smp_processor_id(), bp->cpumask))
+ arch_update_kernel_hw_breakpoint(NULL);
+ smp_call_function_many(bp->cpumask,
+ arch_update_kernel_hw_breakpoint, NULL, 1);
+ goto out;
+ }
+
+ /* Enable/disable the user-space breakpoint */
+ for (i = 0; i < hbp_kernel_pos; i++) {
+ if (thread->hbp[i] != bp)
+ continue;
+ arch_update_user_hw_breakpoint(i, tsk);
+ if (tsk == current)
+ arch_install_thread_hw_breakpoint(tsk);
+ break;
+ }
+out:
+ spin_unlock_bh(&hw_breakpoint_lock);
+
+}
+
+/**
+ * enable_hw_breakpoint - re-enable a breakpoint previously disabled
+ * @bp: pointer to the breakpoint structure to be enabled
+ * @tsk: pointer to 'task_struct' of the process (for user-space breakpoints)
+ *
+ * Re-enable or disable a breakpoint, previously disabled using
+ * disable_hw_breakpoint()
+ */
+void enable_hw_breakpoint(struct hw_breakpoint *bp, struct task_struct *tsk)
+{
+ bp->enabled = 1;
+ update_enable_status_hbp(bp, tsk);
+}
+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
+ * @tsk: pointer to 'task_struct' of the process (for user-space breakpoints)
+ *
+ * Disable a breakpoint without actually losing the registration. Re-enable it
+ * again using enable_hw_breakpoint()
+ */
+void disable_hw_breakpoint(struct hw_breakpoint *bp, struct task_struct *tsk)
+{
+ bp->enabled = 0;
+ update_enable_status_hbp(bp, tsk);
+}
+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 */


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