linux-kernel - [PATCH v3 1/5] hw_breakpoint: Add step

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Date:   Mon, 31 Jul 2017 16:10:29 +0530
From:   Pratyush Anand <panand@...hat.com>
To:     linux-arm-kernel@...ts.infradead.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     mark.rutland@....com, will.deacon@....com, huawei.libin@...wei.com,
        takahiro.akashi@...aro.org, Pratyush Anand <panand@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 1/5] hw_breakpoint: Add step_needed event attribute

Architecture like ARM64 currently allows to use default hw breakpoint
single step handler only to perf. However, some other users like few
systemtap tests or kernel test in
samples/hw_breakpoint/data_breakpoint.c can also work with default step
handler implementation.

Therefore, this patch introduces a flag 'step_needed' in struct
hw_perf_event, so that arch specific code(specially on arm64) can make a
decision to enable single stepping.

Any architecture which is not using this field will not have any
side effect.

Signed-off-by: Pratyush Anand <panand@...hat.com>
---
 include/linux/hw_breakpoint.h | 6 ++++++
 include/linux/perf_event.h    | 6 ++++++
 kernel/events/core.c          | 2 ++
 3 files changed, 14 insertions(+)

diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index 0464c85e63fd..b9ac9629bf74 100644
--- a/include/linux/hw_breakpoint.h
+++ b/include/linux/hw_breakpoint.h
@@ -38,6 +38,12 @@ static inline int hw_breakpoint_type(struct perf_event *bp)
 	return bp->attr.bp_type;
 }
 
+static inline bool
+hw_breakpoint_needs_single_step(struct perf_event *bp)
+{
+	return bp->hw.step_needed;
+}
+
 static inline unsigned long hw_breakpoint_len(struct perf_event *bp)
 {
 	return bp->attr.bp_len;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 24a635887f28..7da951f94b47 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -233,6 +233,12 @@ struct hw_perf_event {
 	 */
 	u64				freq_time_stamp;
 	u64				freq_count_stamp;
+	/*
+	 * A HW breakpoint user can either have it's own step handling
+	 * mechanism or it can use default step handling meachanism defined
+	 * by arch code. Set step_needed to use default mechanism.
+	 */
+	int				step_needed;
 #endif
 };
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6c4e523dc1e2..66ce5574e778 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9444,9 +9444,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 	} else if (is_write_backward(event)){
 		event->overflow_handler = perf_event_output_backward;
 		event->overflow_handler_context = NULL;
+		event->hw.step_needed = 1;
 	} else {
 		event->overflow_handler = perf_event_output_forward;
 		event->overflow_handler_context = NULL;
+		event->hw.step_needed = 1;
 	}
 
 	perf_event__state_init(event);
-- 
2.9.4