linux-kernel - [PATCH] sample/hw_breakpoint: avoid sample hw

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Date:   Mon, 23 Sep 2019 16:09:35 +0800
From:   wangxu <wangxu72@...wei.com>
To:     <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
        <mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
        <namhyung@...nel.org>, <gregkh@...uxfoundation.org>
CC:     <tglx@...utronix.de>, <rfontana@...hat.com>, <allison@...utok.net>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] sample/hw_breakpoint: avoid sample hw_breakpoint recursion for arm/arm64

From: Wang Xu <wangxu72@...wei.com>

For x86/ppc, hw_breakpoint is triggered after the instruction is
executed.

For arm/arm64, which is triggered before the instruction executed.
Arm/arm64 skips the instruction by using single step. But it only
supports default overflow_handler.

This patch provides a chance to avoid sample hw_breakpoint recursion
for arm/arm64 by adding 'struct perf_event_attr.bp_step'.

Signed-off-by: Wang Xu <wangxu72@...wei.com>
---
 include/linux/perf_event.h              | 3 +++
 include/uapi/linux/perf_event.h         | 3 ++-
 samples/hw_breakpoint/data_breakpoint.c | 1 +
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 61448c1..f270eb7 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1024,6 +1024,9 @@ extern int perf_event_output(struct perf_event *event,
 		return true;
 	if (unlikely(event->overflow_handler == perf_event_output_backward))
 		return true;
+	/* avoid sample hw_breakpoint recursion */
+	if (unlikely(event->attr.bp_step))
+		return true;
 	return false;
 }
 
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index bb7b271..95b81c2 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -375,7 +375,8 @@ struct perf_event_attr {
 				ksymbol        :  1, /* include ksymbol events */
 				bpf_event      :  1, /* include bpf events */
 				aux_output     :  1, /* generate AUX records instead of events */
-				__reserved_1   : 32;
+				bp_step        :  1,
+				__reserved_1   : 31;
 
 	union {
 		__u32		wakeup_events;	  /* wakeup every n events */
diff --git a/samples/hw_breakpoint/data_breakpoint.c b/samples/hw_breakpoint/data_breakpoint.c
index c585047..9fe1351 100644
--- a/samples/hw_breakpoint/data_breakpoint.c
+++ b/samples/hw_breakpoint/data_breakpoint.c
@@ -46,6 +46,7 @@ static int __init hw_break_module_init(void)
 	attr.bp_addr = kallsyms_lookup_name(ksym_name);
 	attr.bp_len = HW_BREAKPOINT_LEN_4;
 	attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
+	attr.bp_step = true;
 
 	sample_hbp = register_wide_hw_breakpoint(&attr, sample_hbp_handler, NULL);
 	if (IS_ERR((void __force *)sample_hbp)) {
-- 
1.8.5.6