[PATCH 4/4] wcn36xx: Put DXE block into reset before freeing memory
Bryan O'Donoghue
bryan.odonoghue at linaro.org
Sat Oct 16 18:28:00 PDT 2021
On 15/10/2021 14:17, Bryan O'Donoghue wrote:
> When deiniting the DXE hardware we should reset the block to ensure there
> is no spurious DMA write transaction from the downstream WCNSS to upstream
> MSM at a skbuff address we will have released.
>
> This is actually a pretty serious bug. Immediately after the reset we
> release skbs, skbs which are from the perspective of the WCNSS DXE still
> valid addresses for DMA.
>
> Without first placing the DXE block into reset, it is possible for an
> upstream DMA transaction to write to skbs we have freed.
>
> We have seen some backtraces from usage in testing on 50k+ devices which
> indicates an invalid RX of an APs beacon to unmapped memory.
>
> The logical conclusion is that an RX transaction happened to a region of
> memory that was previously valid but was subsequently released.
>
> The only time such a window of opportunity exists is when we have
> deallocated the skbs attached to the DMA BDs in other words after doing
> wcn36xx_stop().
>
> If we free the skbs on the DMA channel, we need to make sure we have
> quiesced potential DMA on that channel prior to freeing.
>
> This patch should eliminate that error.
>
> Fixes: 8e84c2582169 ("wcn36xx: mac80211 driver for Qualcomm WCN3660/WCN3680 hardware")
> Signed-off-by: Bryan O'Donoghue <bryan.odonoghue at linaro.org>
> ---
> drivers/net/wireless/ath/wcn36xx/dxe.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/net/wireless/ath/wcn36xx/dxe.c b/drivers/net/wireless/ath/wcn36xx/dxe.c
> index e89002502869a..56f605c23f36c 100644
> --- a/drivers/net/wireless/ath/wcn36xx/dxe.c
> +++ b/drivers/net/wireless/ath/wcn36xx/dxe.c
> @@ -1020,6 +1020,8 @@ int wcn36xx_dxe_init(struct wcn36xx *wcn)
>
> void wcn36xx_dxe_deinit(struct wcn36xx *wcn)
> {
> + int reg_data = 0;
> +
> /* Disable channel interrupts */
> wcn36xx_dxe_disable_ch_int(wcn, WCN36XX_INT_MASK_CHAN_RX_H);
> wcn36xx_dxe_disable_ch_int(wcn, WCN36XX_INT_MASK_CHAN_RX_L);
> @@ -1035,6 +1037,10 @@ void wcn36xx_dxe_deinit(struct wcn36xx *wcn)
> wcn->tx_ack_skb = NULL;
> }
>
> + /* Put the DXE block into reset before freeing memory */
> + reg_data = WCN36XX_DXE_REG_RESET;
> + wcn36xx_dxe_write_register(wcn, WCN36XX_DXE_REG_CSR_RESET, reg_data);
> +
> wcn36xx_dxe_ch_free_skbs(wcn, &wcn->dxe_rx_l_ch);
> wcn36xx_dxe_ch_free_skbs(wcn, &wcn->dxe_rx_h_ch);
>
>
Johannes asked me separately if we need to wait for the quiesence to
complete.
I don't see that downstream but, that doesn't mean we shouldn't do it.
So I'll investigate that.
Also - now that I look at this code, this being the second usage of the
CSR_RESET like this, also means the reset can be functionally decomposed
into a routine.
So - I'll look into the first and definitely do the second as a V2
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