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

[Yabin Cui <yabinc@google.com>]

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.

Signed-off-by: Yabin Cui <yabinc@google.com>
---
 drivers/hwtracing/coresight/coresight-tmc-etr.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
index 17006705287a..697e68d492af 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;
@@ -1423,7 +1424,6 @@ static void tmc_etr_sync_perf_buffer(struct etr_perf_buffer *etr_perf)
 	pg_offset = head & (PAGE_SIZE - 1);
 	dst_pages = (char **)etr_perf->pages;
 	src_offset = etr_buf->offset;
-	to_copy = etr_buf->len;
 
 	while (to_copy > 0) {
 		/*
@@ -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
-- 
2.22.0.770.g0f2c4a37fd-goog