On 5/26/2025 7:48 PM, Johan Hovold wrote:

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

Tested-on: WCN6855 hw2.1 WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.41

Fixes: d5c65159f289 ("ath11k: driver for Qualcomm IEEE 802.11ax devices") Cc: stable@vger.kernel.org # 5.6 Signed-off-by: Johan Hovold johan+linaro@kernel.org

---

drivers/net/wireless/ath/ath11k/dp_rx.c | 19 +++++++++++++++++++ drivers/net/wireless/ath/ath11k/dp_tx.c | 3 +++ 2 files changed, 22 insertions(+)

diff --git a/drivers/net/wireless/ath/ath11k/dp_rx.c b/drivers/net/wireless/ath/ath11k/dp_rx.c index ea2959305dec..dfe2d889c20f 100644 --- a/drivers/net/wireless/ath/ath11k/dp_rx.c +++ b/drivers/net/wireless/ath/ath11k/dp_rx.c @@ -3851,6 +3851,9 @@ int ath11k_dp_process_rx_err(struct ath11k_base *ab, struct napi_struct *napi, ath11k_hal_srng_access_begin(ab, srng);

• /* Make sure descriptor is read after the head pointer. */
• dma_rmb();

Thanks Johan, for continuing to follow up on this issue. I have some different opinions.

This change somewhat deviates from the fix approach described in https://lore.kernel.org/all/20250321095219.19369-1-johan+linaro@kernel.org/. In this case, the descriptor might be accessed before it is updated or while it is still being updated. Therefore, a dma_rmb() should be added after the call to ath11k_hal_srng_dst_get_next_entry() and before accessing ath11k_hal_ce_dst_status_get_length(), to ensure that the DMA has completed before reading the descriptor.

However, in this patch, the memory barrier is used to protect the head pointer (HP). I don't think a memory barrier is necessary for HP, because even if an outdated HP is fetched, ath11k_hal_srng_dst_get_next_entry() will return NULL and exit safely. So, placing the memory barrier inside ath11k_hal_srng_dst_get_next_entry() would be more appropriate.

@@ -678,6 +678,8 @@ u32 *ath11k_hal_srng_dst_get_next_entry(struct ath11k_base *ab, if (srng->flags & HAL_SRNG_FLAGS_CACHED) ath11k_hal_srng_prefetch_desc(ab, srng);

+ dma_rmb(); + return desc; }

while (budget && (desc = ath11k_hal_srng_dst_get_next_entry(ab, srng))) { struct hal_reo_dest_ring *reo_desc = (struct hal_reo_dest_ring *)desc; @@ -4154,6 +4157,9 @@ int ath11k_dp_rx_process_wbm_err(struct ath11k_base *ab, ath11k_hal_srng_access_begin(ab, srng);

• /* Make sure descriptor is read after the head pointer. */
• dma_rmb();
• while (budget) { rx_desc = ath11k_hal_srng_dst_get_next_entry(ab, srng); if (!rx_desc)

@@ -4280,6 +4286,9 @@ int ath11k_dp_process_rxdma_err(struct ath11k_base *ab, int mac_id, int budget) ath11k_hal_srng_access_begin(ab, srng);

• /* Make sure descriptor is read after the head pointer. */
• dma_rmb();
• while (quota-- && (desc = ath11k_hal_srng_dst_get_next_entry(ab, srng))) { ath11k_hal_rx_reo_ent_paddr_get(ab, desc, &paddr, &desc_bank);

@@ -4353,6 +4362,9 @@ void ath11k_dp_process_reo_status(struct ath11k_base *ab) ath11k_hal_srng_access_begin(ab, srng);

• /* Make sure descriptor is read after the head pointer. */
• dma_rmb();
• while ((reo_desc = ath11k_hal_srng_dst_get_next_entry(ab, srng))) { tag = FIELD_GET(HAL_SRNG_TLV_HDR_TAG, *reo_desc);

@@ -5168,6 +5180,9 @@ static void ath11k_dp_rx_mon_dest_process(struct ath11k *ar, int mac_id, rx_bufs_used = 0; rx_mon_stats = &pmon->rx_mon_stats;

• /* Make sure descriptor is read after the head pointer. */
• dma_rmb();
• while ((ring_entry = ath11k_hal_srng_dst_peek(ar->ab, mon_dst_srng))) { struct sk_buff *head_msdu, *tail_msdu;

@@ -5630,6 +5645,10 @@ static int ath11k_dp_full_mon_process_rx(struct ath11k_base *ab, int mac_id, spin_lock_bh(&mon_dst_srng->lock); ath11k_hal_srng_access_begin(ar->ab, mon_dst_srng);

• /* Make sure descriptor is read after the head pointer. */
• dma_rmb();
• while ((ring_entry = ath11k_hal_srng_dst_peek(ar->ab, mon_dst_srng))) { head_msdu = NULL; tail_msdu = NULL;

diff --git a/drivers/net/wireless/ath/ath11k/dp_tx.c b/drivers/net/wireless/ath/ath11k/dp_tx.c index 8522c67baabf..549d17d90503 100644 --- a/drivers/net/wireless/ath/ath11k/dp_tx.c +++ b/drivers/net/wireless/ath/ath11k/dp_tx.c @@ -700,6 +700,9 @@ void ath11k_dp_tx_completion_handler(struct ath11k_base *ab, int ring_id) ath11k_hal_srng_access_begin(ab, status_ring);

• /* Make sure descriptor is read after the head pointer. */
• dma_rmb();
• while ((ATH11K_TX_COMPL_NEXT(tx_ring->tx_status_head) != tx_ring->tx_status_tail) && (desc = ath11k_hal_srng_dst_get_next_entry(ab, status_ring))) {