Re: [PATCH 1/3] wifi: ath11k: fix dest ring-buffer corruption

[Miaoqing Pan <quic_miaoqing@quicinc.com>]

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because even if an outdated HP is fetched, 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))) {