[Patch 2/2] HW-BKPT: Allow kernel breakpoints to be modified through a new API

["K.Prasad" <prasad@linux.vnet.ibm.com>]

[-- Attachment #1: modify_kernel_hbp_02 --]
[-- Type: text/plain, Size: 3125 bytes --]

Introduce modify_kernel_hw_breakpoint() API that can quickly change the
characteristics (such as address, length, type but not cpumask) of a
kernel-space breakpoint without having to unregister first and then
re-register it.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
 include/asm-generic/hw_breakpoint.h |    2 +
 kernel/hw_breakpoint.c              |   49 ++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

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
@@ -133,6 +133,8 @@ extern void unregister_user_hw_breakpoin
  * Kernel breakpoints are not associated with any particular thread.
  */
 extern int register_kernel_hw_breakpoint(struct hw_breakpoint *bp);
+extern int modify_kernel_hw_breakpoint(struct hw_breakpoint *old_bp,
+					struct hw_breakpoint *new_bp);
 extern void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp);
 
 extern unsigned int hbp_kernel_pos;
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
@@ -362,6 +362,55 @@ err_ret:
 }
 EXPORT_SYMBOL_GPL(register_kernel_hw_breakpoint);
 
+/**
+ * modify_kernel_hw_breakpoint - modify characteristics of a previously registered breakpoint request
+ * @old_bp: pointer to the registered breakpoint structure
+ * @new_bp: pointer to the breakpoint structure that replaces @old_bp
+ *
+ */
+int modify_kernel_hw_breakpoint(struct hw_breakpoint *old_bp,
+				   struct hw_breakpoint *new_bp)
+{
+	int i, rc;
+	unsigned int cpu;
+	const cpumask_t *new_cpumask = new_bp->cpumask;
+
+	/* Default to ALL CPUs if cpumask is not specified */
+	if (!new_cpumask)
+		new_cpumask = new_bp->cpumask = cpu_possible_mask;
+	/*
+	 * The user cannot modify the cpumask of the registered breakpoint
+	 * It requires non-trivial amount of code and new data-structures to
+	 * allow a change in cpumask value. The user must instead 'unregister'
+	 * and re-register a new breakpoint if 'cpumask' should be changed
+	 */
+	if (!cpumask_equal(old_bp->cpumask, new_cpumask))
+		return -EINVAL;
+
+	rc = arch_validate_hwbkpt_settings(new_bp, NULL);
+	if (rc)
+		return rc;
+
+	spin_lock_bh(&hw_breakpoint_lock);
+	for_each_cpu(cpu, new_cpumask) {
+		for (i = HBP_NUM-1; i >= hbp_kernel_pos; i--) {
+			if (per_cpu(this_hbp_kernel[i], cpu) == old_bp) {
+				per_cpu(this_hbp_kernel[i], cpu) = new_bp;
+				break;
+			}
+		}
+	}
+
+	if (cpumask_test_cpu(smp_processor_id(), new_cpumask))
+		arch_update_kernel_hw_breakpoint(NULL);
+	smp_call_function_many(new_cpumask,
+				arch_update_kernel_hw_breakpoint, NULL, 1);
+
+	spin_unlock_bh(&hw_breakpoint_lock);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(modify_kernel_hw_breakpoint);
+
 /* Removes breakpoint structure from the per-cpu breakpoint data-structure */
 static void remove_each_cpu_kernel_hbp(void *bp_param)
 {