linux-kernel - [PATCH v2 1/4] wifi: ath12k: fix dest ring-buffer corruption

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Message-ID: <20250604144509.28374-2-johan+linaro@kernel.org>
Date: Wed,  4 Jun 2025 16:45:06 +0200
From: Johan Hovold <johan+linaro@...nel.org>
To: Jeff Johnson <jjohnson@...nel.org>
Cc: Miaoqing Pan <quic_miaoqing@...cinc.com>,
	Remi Pommarel <repk@...plefau.lt>,
	Baochen Qiang <quic_bqiang@...cinc.com>,
	linux-wireless@...r.kernel.org,
	ath12k@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Johan Hovold <johan+linaro@...nel.org>,
	stable@...r.kernel.org
Subject: [PATCH v2 1/4] wifi: ath12k: fix dest ring-buffer corruption

Add the missing memory barrier to make sure that destination ring
descriptors are read after the head pointers to avoid using stale data
on weakly ordered architectures like aarch64.

The barrier is added to the ath12k_hal_srng_access_begin() helper for
symmetry with follow-on fixes for source ring buffer corruption which
will add barriers to ath12k_hal_srng_access_end().

Note that this may fix the empty descriptor issue recently worked around
by commit 51ad34a47e9f ("wifi: ath12k: Add drop descriptor handling for
monitor ring").

Tested-on: WCN7850 hw2.0 WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Fixes: d889913205cf ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices")
Cc: stable@...r.kernel.org	# 6.3
Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
---
 drivers/net/wireless/ath/ath12k/ce.c  |  3 ---
 drivers/net/wireless/ath/ath12k/hal.c | 17 ++++++++++++++---
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wireless/ath/ath12k/ce.c b/drivers/net/wireless/ath/ath12k/ce.c
index 740586fe49d1..b66d23d6b2bd 100644
--- a/drivers/net/wireless/ath/ath12k/ce.c
+++ b/drivers/net/wireless/ath/ath12k/ce.c
@@ -343,9 +343,6 @@ static int ath12k_ce_completed_recv_next(struct ath12k_ce_pipe *pipe,
 		goto err;
 	}
 
-	/* Make sure descriptor is read after the head pointer. */
-	dma_rmb();
-
 	*nbytes = ath12k_hal_ce_dst_status_get_length(desc);
 
 	*skb = pipe->dest_ring->skb[sw_index];
diff --git a/drivers/net/wireless/ath/ath12k/hal.c b/drivers/net/wireless/ath/ath12k/hal.c
index 91d5126ca149..9eea13ed5565 100644
--- a/drivers/net/wireless/ath/ath12k/hal.c
+++ b/drivers/net/wireless/ath/ath12k/hal.c
@@ -2126,13 +2126,24 @@ void *ath12k_hal_srng_src_get_next_reaped(struct ath12k_base *ab,
 
 void ath12k_hal_srng_access_begin(struct ath12k_base *ab, struct hal_srng *srng)
 {
+	u32 hp;
+
 	lockdep_assert_held(&srng->lock);
 
-	if (srng->ring_dir == HAL_SRNG_DIR_SRC)
+	if (srng->ring_dir == HAL_SRNG_DIR_SRC) {
 		srng->u.src_ring.cached_tp =
 			*(volatile u32 *)srng->u.src_ring.tp_addr;
-	else
-		srng->u.dst_ring.cached_hp = READ_ONCE(*srng->u.dst_ring.hp_addr);
+	} else {
+		hp = READ_ONCE(*srng->u.dst_ring.hp_addr);
+
+		if (hp != srng->u.dst_ring.cached_hp) {
+			srng->u.dst_ring.cached_hp = hp;
+			/* Make sure descriptor is read after the head
+			 * pointer.
+			 */
+			dma_rmb();
+		}
+	}
 }
 
 /* Update cached ring head/tail pointers to HW. ath12k_hal_srng_access_begin()
-- 
2.49.0