linux-kernel - [EDT] [PATCH 1/1] Fix: hw watchpoint continually triggers callback

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Date:	Tue, 12 May 2015 11:48:12 +0000 (GMT)
From:	Maninder Singh <maninder1.s@...sung.com>
To:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux@....linux.org.uk, will.deacon@....com
Cc:	"v.narang@...sung.com" <v.narang@...sung.com>,
	AJEET YADAV <ajeet.y@...sung.com>,
	Amit Arora <amit.arora@...sung.com>,
	AKHILESH KUMAR <akhilesh.k@...sung.com>
Subject: [EDT] [PATCH 1/1] Fix: hw watchpoint continually triggers callback

EP-2DAD0AFA905A4ACB804C4F82A001242F

On ARM, when a watchpoint is registered using register_wide_hw_breakpoint, 
the callback handler endlessly runs until the watchpoint is unregistered.
The reason for this issue is debug interrupts gets raised before executing the instruction,
and after interrupt handling ARM tries to execute the same instruction again , which results
in interrupt getting raised again.

This patch fixes this issue by using KPROBES (getting the instruction executed and incrementing PC
to next instruction).

Signed-off-by: Vaneet Narang <v.narang@...sung.com>
Signed-off-by: Maninder Singh <maninder1.s@...sung.com>
Reviewed-by: Amit Arora <amit.arora@...sung.com>
Reviewed-by: Ajeet Yadav <ajeet.y@...sung.com>
---
 arch/arm/kernel/hw_breakpoint.c |   18 ++++++++++++++++++
 1 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index dc7d0a9..ec72f86 100644
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -37,6 +37,9 @@
 #include <asm/hw_breakpoint.h>
 #include <asm/kdebug.h>
 #include <asm/traps.h>
+#ifdef CONFIG_KPROBES
+#include <linux/kprobes.h>
+#endif
 
 /* Breakpoint currently in use for each BRP. */
 static DEFINE_PER_CPU(struct perf_event *, bp_on_reg[ARM_MAX_BRP]);
@@ -757,6 +760,21 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr,
 		 */
 		if (!wp->overflow_handler)
 			enable_single_step(wp, instruction_pointer(regs));
+#ifdef CONFIG_KPROBES
+		else {
+			struct kprobe kp;
+			unsigned long flags;
+
+			arch_uninstall_hw_breakpoint(wp);
+			kp.addr = (kprobe_opcode_t *)instruction_pointer(regs);
+			if (!arch_prepare_kprobe(&kp)) {
+				local_irq_save(flags);
+				kp.ainsn.insn_singlestep(&kp, regs);
+				local_irq_restore(flags);
+			}
+			arch_install_hw_breakpoint(wp);
+		}
+#endif
 
 unlock:
 		rcu_read_unlock();
-- 
1.7.1


Thanks ,
Maninder Singh