5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Chunkai Deng <redacted>
commit 786439ad58763e04b91bc2ec5f590e463939f197 upstream.
glink_smem_rx_peek() reads the RX FIFO payload after the caller has
determined data is available via glink_smem_rx_avail(), which reads the
remote-updated head index. A control dependency between the head read
and the subsequent payload read does not order the two loads, so the
CPU may speculatively read the FIFO before observing the head update
and consume stale data the remote has not yet published.
Add rmb() in glink_smem_rx_peek() before the memcpy_fromio() so the
availability (head) read is ordered ahead of the FIFO payload read,
matching the consumer pattern in
Documentation/core-api/circular-buffers.rst.
Fixes: caf989c350e8 ("rpmsg: glink: Introduce glink smem based transport")
Cc: <redacted>
Signed-off-by: Chunkai Deng <redacted>
Reviewed-by: Konrad Dybcio <redacted>
Link: https://lore.kernel.org/r/20260618-rpmsg-glink-smem-mb-v1-1-68a026453a69@oss.qualcomm.com (local)
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/rpmsg/qcom_glink_smem.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/drivers/rpmsg/qcom_glink_smem.c
+++ b/drivers/rpmsg/qcom_glink_smem.c
@@ -88,6 +88,13 @@ static void glink_smem_rx_peak(struct qc
if (tail >= pipe->native.length)
tail -= pipe->native.length;
+ /*
+ * Order the availability (head) read in glink_smem_rx_avail()
+ * against the FIFO payload read below, so APPS never consumes
+ * stale data the remote has not yet published.
+ */
+ rmb();
+
len = min_t(size_t, count, pipe->native.length - tail);
if (len)
memcpy_fromio(data, pipe->fifo + tail, len);