linux-kernel - Re: [PATCH v2 1/5] wifi: ath11k: fix dest ring-buffer corruption

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Message-ID: <b3432e80-9a54-4338-8991-606d1484dcc5@quicinc.com>
Date: Thu, 5 Jun 2025 17:12:57 +0800
From: Baochen Qiang <quic_bqiang@...cinc.com>
To: Johan Hovold <johan+linaro@...nel.org>, Jeff Johnson <jjohnson@...nel.org>
CC: Miaoqing Pan <quic_miaoqing@...cinc.com>, <linux-wireless@...r.kernel.org>,
        <ath11k@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] wifi: ath11k: fix dest ring-buffer corruption



On 6/4/2025 10:34 PM, Johan Hovold wrote:
> 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 ath11k_hal_srng_access_begin() helper for
> symmetry with follow-on fixes for source ring buffer corruption which
> will add barriers to ath11k_hal_srng_access_end().
> 
> 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@...r.kernel.org	# 5.6
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
>  drivers/net/wireless/ath/ath11k/ce.c    |  3 ---
>  drivers/net/wireless/ath/ath11k/dp_rx.c |  3 ---
>  drivers/net/wireless/ath/ath11k/hal.c   | 12 +++++++++++-
>  3 files changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/ath11k/ce.c b/drivers/net/wireless/ath/ath11k/ce.c
> index 9d8efec46508..39d9aad33bc6 100644
> --- a/drivers/net/wireless/ath/ath11k/ce.c
> +++ b/drivers/net/wireless/ath/ath11k/ce.c
> @@ -393,9 +393,6 @@ static int ath11k_ce_completed_recv_next(struct ath11k_ce_pipe *pipe,
>  		goto err;
>  	}
>  
> -	/* Make sure descriptor is read after the head pointer. */
> -	dma_rmb();
> -
>  	*nbytes = ath11k_hal_ce_dst_status_get_length(desc);
>  
>  	*skb = pipe->dest_ring->skb[sw_index];
> diff --git a/drivers/net/wireless/ath/ath11k/dp_rx.c b/drivers/net/wireless/ath/ath11k/dp_rx.c
> index ea2959305dec..d8dab182a9af 100644
> --- a/drivers/net/wireless/ath/ath11k/dp_rx.c
> +++ b/drivers/net/wireless/ath/ath11k/dp_rx.c
> @@ -2650,9 +2650,6 @@ int ath11k_dp_process_rx(struct ath11k_base *ab, int ring_id,
>  try_again:
>  	ath11k_hal_srng_access_begin(ab, srng);
>  
> -	/* Make sure descriptor is read after the head pointer. */
> -	dma_rmb();
> -
>  	while (likely(desc =
>  	      (struct hal_reo_dest_ring *)ath11k_hal_srng_dst_get_next_entry(ab,
>  									     srng))) {
> diff --git a/drivers/net/wireless/ath/ath11k/hal.c b/drivers/net/wireless/ath/ath11k/hal.c
> index 8cb1505a5a0c..921114686ba3 100644
> --- a/drivers/net/wireless/ath/ath11k/hal.c
> +++ b/drivers/net/wireless/ath/ath11k/hal.c
> @@ -823,13 +823,23 @@ u32 *ath11k_hal_srng_src_peek(struct ath11k_base *ab, struct hal_srng *srng)
>  
>  void ath11k_hal_srng_access_begin(struct ath11k_base *ab, struct hal_srng *srng)
>  {
> +	u32 hp;
> +
>  	lockdep_assert_held(&srng->lock);
>  
>  	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);
> +		hp = READ_ONCE(*srng->u.dst_ring.hp_addr);
> +
> +		if (hp != srng->u.dst_ring.cached_hp) {

My ath12k comments apply here: this consumes more CPU cycles

> +			srng->u.dst_ring.cached_hp = hp;
> +			/* Make sure descriptor is read after the head
> +			 * pointer.
> +			 */
> +			dma_rmb();
> +		}
>  
>  		/* Try to prefetch the next descriptor in the ring */
>  		if (srng->flags & HAL_SRNG_FLAGS_CACHED)