powerpc/watchpoint: Use loop for thread_struct->ptrace_bps

ptrace_bps is already an array of size HBP_NUM_MAX. But we use
hardcoded index 0 while fetching/updating it. Convert such code
to loop over array.

ptrace interface to use multiple watchpoint remains same. eg:
two PPC_PTRACE_SETHWDEBUG calls will create two watchpoint if
underneath hw supports it.
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Michael Neuling <mikey@neuling.org>
Link: https://lore.kernel.org/r/20200514111741.97993-11-ravi.bangoria@linux.ibm.com

arch/powerpc/kernel/hw_breakpoint.c

@@ -420,10 +420,13 @@ NOKPROBE_SYMBOL(hw_breakpoint_exceptions_notify);
  */
 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 {
+	int i;
 	struct thread_struct *t = &tsk->thread;
 
-	unregister_hw_breakpoint(t->ptrace_bps[0]);
-	t->ptrace_bps[0] = NULL;
+	for (i = 0; i < nr_wp_slots(); i++) {
+		unregister_hw_breakpoint(t->ptrace_bps[i]);
+		t->ptrace_bps[i] = NULL;
+	}
 }
 
 void hw_breakpoint_pmu_read(struct perf_event *bp)

arch/powerpc/kernel/process.c

@@ -1604,6 +1604,9 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
 	void (*f)(void);
 	unsigned long sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
 	struct thread_info *ti = task_thread_info(p);
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	int i;
+#endif
 
 	klp_init_thread_info(p);
 
@@ -1663,7 +1666,8 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
 	p->thread.ksp_limit = (unsigned long)end_of_stack(p);
 #endif
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
-	p->thread.ptrace_bps[0] = NULL;
+	for (i = 0; i < nr_wp_slots(); i++)
+		p->thread.ptrace_bps[i] = NULL;
 #endif
 
 	p->thread.fp_save_area = NULL;

arch/powerpc/kernel/ptrace/ptrace-noadv.c

@@ -168,6 +168,19 @@ int ptrace_set_debugreg(struct task_struct *task, unsigned long addr, unsigned l
 	return 0;
 }
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+static int find_empty_ptrace_bp(struct thread_struct *thread)
+{
+	int i;
+
+	for (i = 0; i < nr_wp_slots(); i++) {
+		if (!thread->ptrace_bps[i])
+			return i;
+	}
+	return -1;
+}
+#endif
+
 static int find_empty_hw_brk(struct thread_struct *thread)
 {
 	int i;
@@ -217,8 +230,9 @@ long ppc_set_hwdebug(struct task_struct *child, struct ppc_hw_breakpoint *bp_inf
 		len = 1;
 	else
 		return -EINVAL;
-	bp = thread->ptrace_bps[0];
-	if (bp)
+
+	i = find_empty_ptrace_bp(thread);
+	if (i < 0)
 		return -ENOSPC;
 
 	/* Create a new breakpoint request if one doesn't exist already */
@@ -228,13 +242,13 @@ long ppc_set_hwdebug(struct task_struct *child, struct ppc_hw_breakpoint *bp_inf
 	arch_bp_generic_fields(brk.type, &attr.bp_type);
 
 	bp = register_user_hw_breakpoint(&attr, ptrace_triggered, NULL, child);
-	thread->ptrace_bps[0] = bp;
+	thread->ptrace_bps[i] = bp;
 	if (IS_ERR(bp)) {
-		thread->ptrace_bps[0] = NULL;
+		thread->ptrace_bps[i] = NULL;
 		return PTR_ERR(bp);
 	}
 
-	return 1;
+	return i + 1;
 #endif /* CONFIG_HAVE_HW_BREAKPOINT */
 
 	if (bp_info->addr_mode != PPC_BREAKPOINT_MODE_EXACT)
@@ -263,10 +277,10 @@ long ppc_del_hwdebug(struct task_struct *child, long data)
 		return -EINVAL;
 
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
-	bp = thread->ptrace_bps[0];
+	bp = thread->ptrace_bps[data - 1];
 	if (bp) {
 		unregister_hw_breakpoint(bp);
-		thread->ptrace_bps[0] = NULL;
+		thread->ptrace_bps[data - 1] = NULL;
 	} else {
 		ret = -ENOENT;
 	}