linux-kernel - [PATCH v2] coresight: tmc-etr: Fix updating buffer in not-snapshot mode.

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Message-Id: <20190812221154.46875-1-yabinc@google.com>
Date:   Mon, 12 Aug 2019 15:11:54 -0700
From:   Yabin Cui <yabinc@...gle.com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Yabin Cui <yabinc@...gle.com>
Subject: [PATCH v2] coresight: tmc-etr: Fix updating buffer in not-snapshot mode.

TMC etr always copies all available data to perf aux buffer, which
may exceed the available space in perf aux buffer. It isn't suitable
for not-snapshot mode, because:
1) It may overwrite previously written data.
2) It may make the perf_event_mmap_page->aux_head report having more
or less data than the reality.

So change to only copy the latest data fitting the available space in
perf aux buffer.

Signed-off-by: Yabin Cui <yabinc@...gle.com>
---

v1 -> v2: copy the latest data instead of the earliest data.

---
 .../hwtracing/coresight/coresight-tmc-etr.c    | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index 17006705287a..676dcb4cf0e2 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
@@ -1410,9 +1410,10 @@ static void tmc_free_etr_buffer(void *config)
  * tmc_etr_sync_perf_buffer: Copy the actual trace data from the hardware
  * buffer to the perf ring buffer.
  */
-static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
+static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf,
+				     unsigned long to_copy)
 {
-	long bytes, to_copy;
+	long bytes;
 	long pg_idx, pg_offset, src_offset;
 	unsigned long head = etr_perf->head;
 	char **dst_pages, *src_buf;
@@ -1422,8 +1423,7 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
 	pg_idx = head >> PAGE_SHIFT;
 	pg_offset = head & (PAGE_SIZE - 1);
 	dst_pages = (char **)etr_perf->pages;
-	src_offset = etr_buf->offset;
-	to_copy = etr_buf->len;
+	src_offset = etr_buf->offset + etr_buf->len - to_copy;
 
 	while (to_copy > 0) {
 		/*
@@ -1434,6 +1434,8 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
 		 *  3) what is available in the destination page.
 		 * in one iteration.
 		 */
+		if (src_offset >= etr_buf->size)
+			src_offset -= etr_buf->size;
 		bytes = tmc_etr_buf_get_data(etr_buf, src_offset, to_copy,
 					     &src_buf);
 		if (WARN_ON_ONCE(bytes <= 0))
@@ -1454,8 +1456,6 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
 
 		/* Move source pointers */
 		src_offset += bytes;
-		if (src_offset >= etr_buf->size)
-			src_offset -= etr_buf->size;
 	}
 }
 
@@ -1501,7 +1501,11 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
 	spin_unlock_irqrestore(&drvdata->spinlock, flags);
 
 	size = etr_buf->len;
-	tmc_etr_sync_perf_buffer(etr_perf);
+	if (!etr_perf->snapshot && size > handle->size) {
+		size = handle->size;
+		lost = true;
+	}
+	tmc_etr_sync_perf_buffer(etr_perf, size);
 
 	/*
 	 * In snapshot mode we simply increment the head by the number of byte
-- 
2.23.0.rc1.153.gdeed80330f-goog