linux-kernel - [PATCH 1/2] powerpc/hw_breakpoint: move instruction stepping out of hw_breakpoint

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Message-Id: <20190910102422.23233-2-ravi.bangoria@linux.ibm.com>
Date:   Tue, 10 Sep 2019 15:54:21 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     mpe@...erman.id.au, mikey@...ling.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        christophe.leroy@....fr,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: [PATCH 1/2] powerpc/hw_breakpoint: move instruction stepping out of hw_breakpoint_handler()

From: Christophe Leroy <christophe.leroy@....fr>

On 8xx, breakpoints stop after executing the instruction, so
stepping/emulation is not needed. Move it into a sub-function and
remove the #ifdefs.

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
Reviewed-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
---
 arch/powerpc/kernel/hw_breakpoint.c | 60 ++++++++++++++++-------------
 1 file changed, 33 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
index c8d1fa2e9d53..28ad3171bb82 100644
--- a/arch/powerpc/kernel/hw_breakpoint.c
+++ b/arch/powerpc/kernel/hw_breakpoint.c
@@ -198,15 +198,43 @@ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
 /*
  * Handle debug exception notifications.
  */
+static bool stepping_handler(struct pt_regs *regs, struct perf_event *bp,
+			     unsigned long addr)
+{
+	int stepped;
+	unsigned int instr;
+
+	/* Do not emulate user-space instructions, instead single-step them */
+	if (user_mode(regs)) {
+		current->thread.last_hit_ubp = bp;
+		regs->msr |= MSR_SE;
+		return false;
+	}
+
+	stepped = 0;
+	instr = 0;
+	if (!__get_user_inatomic(instr, (unsigned int *)regs->nip))
+		stepped = emulate_step(regs, instr);
+
+	/*
+	 * 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) {
+		WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
+			"0x%lx will be disabled.", addr);
+		perf_event_disable_inatomic(bp);
+		return false;
+	}
+	return true;
+}
+
 int hw_breakpoint_handler(struct die_args *args)
 {
 	int rc = NOTIFY_STOP;
 	struct perf_event *bp;
 	struct pt_regs *regs = args->regs;
-#ifndef CONFIG_PPC_8xx
-	int stepped = 1;
-	unsigned int instr;
-#endif
 	struct arch_hw_breakpoint *info;
 	unsigned long dar = regs->dar;
 
@@ -251,31 +279,9 @@ int hw_breakpoint_handler(struct die_args *args)
 	      (dar - bp->attr.bp_addr < bp->attr.bp_len)))
 		info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;
 
-#ifndef CONFIG_PPC_8xx
-	/* Do not emulate user-space instructions, instead single-step them */
-	if (user_mode(regs)) {
-		current->thread.last_hit_ubp = bp;
-		regs->msr |= MSR_SE;
+	if (!IS_ENABLED(CONFIG_PPC_8xx) && !stepping_handler(regs, bp, info->address))
 		goto out;
-	}
-
-	stepped = 0;
-	instr = 0;
-	if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
-		stepped = emulate_step(regs, instr);
 
-	/*
-	 * 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) {
-		WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
-			"0x%lx will be disabled.", info->address);
-		perf_event_disable_inatomic(bp);
-		goto out;
-	}
-#endif
 	/*
 	 * As a policy, the callback is invoked in a 'trigger-after-execute'
 	 * fashion
-- 
2.21.0