SPE and TRBE write padding into their AUX buffers before advancing aux_head. Add the missing write barriers so that a userspace reader on another CPU cannot observe the new head before the padding stores become visible.
AUX producers must make their data visible before publishing aux_head. The required synchronization depends on the trace hardware and CPU memory model, so the barriers belong in the drivers rather than in perf_aux_output_skip() or perf_aux_output_end(). The TRBE change also covers padding inserted by the overwrite erratum workaround before perf_aux_output_end().
Signed-off-by: Leo Yan leo.yan@arm.com --- Leo Yan (2): perf: arm_spe: Order padding before publishing AUX head coresight: trbe: Order padding before publishing AUX head
drivers/hwtracing/coresight/coresight-trbe.c | 2 ++ drivers/perf/arm_spe_pmu.c | 5 ++++- 2 files changed, 6 insertions(+), 1 deletion(-) --- base-commit: 0fcb05b72344f40806cbe810de8872f1698bf053 change-id: 20261015-add_barriers_for_perf_aux_output_skip-70356815b2bd
Best regards,
The driver fills alignment gaps and calls perf_aux_output_skip(), which publishes the new aux_head without a memory barrier. A userspace consumer on another CPU can therefore observe the new head before the padding stores become visible.
Add smp_wmb() between the padding stores and perf_aux_output_skip().
Fixes: d5d9696b0380 ("drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension") Assisted-by: LLM Signed-off-by: Leo Yan leo.yan@arm.com --- drivers/perf/arm_spe_pmu.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c index b70f3fedf0282baba1395ce1116272ec5f961ea8..e105462ec5f38eab4776b0a654ba7c8a84f70f71 100644 --- a/drivers/perf/arm_spe_pmu.c +++ b/drivers/perf/arm_spe_pmu.c @@ -487,8 +487,11 @@ static void arm_spe_pmu_pad_buf(struct perf_output_handle *handle, int len) u64 head = PERF_IDX2OFF(handle->head, buf);
memset(buf->base + head, ARM_SPE_BUF_PAD_BYTE, len); - if (!buf->snapshot) + if (!buf->snapshot) { + /* Order the padding stores before publishing the new aux_head. */ + smp_wmb(); perf_aux_output_skip(handle, len); + } }
static u64 arm_spe_pmu_next_snapshot_off(struct perf_output_handle *handle)
TRBE fills gaps in the AUX buffer before advancing aux_head. Neither perf_aux_output_skip() nor perf_aux_output_end() guarantees ordering of these CPU stores before publishing the new head.
Add smp_wmb() after memset() in __trbe_pad_buf(). This covers alignment padding published by perf_aux_output_skip() and the overwrite erratum padding written by trbe_get_trace_size() before perf_aux_output_end().
Fixes: 3fbf7f011f24 ("coresight: sink: Add TRBE driver") Assisted-by: LLM Signed-off-by: Leo Yan leo.yan@arm.com --- drivers/hwtracing/coresight/coresight-trbe.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c index c7cbca45f2debd4047b93283ea9fe5dd9e1f2ebf..b605121b1dcfed9837c15cd92ff4c42515f39eaf 100644 --- a/drivers/hwtracing/coresight/coresight-trbe.c +++ b/drivers/hwtracing/coresight/coresight-trbe.c @@ -362,6 +362,8 @@ static void trbe_stop_and_truncate_event(struct perf_output_handle *handle) static void __trbe_pad_buf(struct trbe_buf *buf, u64 offset, int len) { memset((void *)buf->trbe_base + offset, ETE_IGNORE_PACKET, len); + /* Order the padding stores before publishing the new aux_head. */ + smp_wmb(); }
static void trbe_pad_buf(struct perf_output_handle *handle, int len)
On 15/10/2026 16:51, Leo Yan wrote:
SPE and TRBE write padding into their AUX buffers before advancing aux_head. Add the missing write barriers so that a userspace reader on another CPU cannot observe the new head before the padding stores become visible.
AUX producers must make their data visible before publishing aux_head. The required synchronization depends on the trace hardware and CPU memory model, so the barriers belong in the drivers rather than in perf_aux_output_skip() or perf_aux_output_end(). The TRBE change also covers padding inserted by the overwrite erratum workaround before perf_aux_output_end().
Signed-off-by: Leo Yan leo.yan@arm.com
Leo Yan (2): perf: arm_spe: Order padding before publishing AUX head coresight: trbe: Order padding before publishing AUX head
drivers/hwtracing/coresight/coresight-trbe.c | 2 ++ drivers/perf/arm_spe_pmu.c | 5 ++++- 2 files changed, 6 insertions(+), 1 deletion(-)
base-commit: 0fcb05b72344f40806cbe810de8872f1698bf053 change-id: 20261015-add_barriers_for_perf_aux_output_skip-70356815b2bd
Best regards,
Reviewed-by: James Clark james.clark@linaro.org
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James Clark -
Leo Yan