ath11k: use cache line aligned buffers for dbring

The DMA buffers of dbring which is used for spectral/cfr
starts at certain offset from original kmalloc() returned buffer.
This is not cache line aligned.
And also driver tries to access the data that is immediately before
this offset address (i.e. buff->paddr) after doing dma map.
This will cause cache line sharing issues and data corruption,
if CPU happen to write back cache after HW has dma'ed the data.

Fix this by mapping a cache line aligned buffer to dma.

Tested on: IPQ8074 hw2.0 AHB WLAN.HK.2.5.0.1-01100-QCAHKSWPL_SILICONZ-1
Signed-off-by: Rameshkumar Sundaram <quic_ramess@quicinc.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1635831693-15962-1-git-send-email-quic_ramess@quicinc.com

drivers/net/wireless/ath/ath11k/dbring.c

@@ -87,17 +87,23 @@ static int ath11k_dbring_fill_bufs(struct ath11k *ar,
 	req_entries = min(num_free, ring->bufs_max);
 	num_remain = req_entries;
 	align = ring->buf_align;
-	size = sizeof(*buff) + ring->buf_sz + align - 1;
+	size = ring->buf_sz + align - 1;
 
 	while (num_remain > 0) {
-		buff = kzalloc(size, GFP_ATOMIC);
+		buff = kzalloc(sizeof(*buff), GFP_ATOMIC);
 		if (!buff)
 			break;
 
+		buff->payload = kzalloc(size, GFP_ATOMIC);
+		if (!buff->payload) {
+			kfree(buff);
+			break;
+		}
 		ret = ath11k_dbring_bufs_replenish(ar, ring, buff);
 		if (ret) {
 			ath11k_warn(ar->ab, "failed to replenish db ring num_remain %d req_ent %d\n",
 				    num_remain, req_entries);
+			kfree(buff->payload);
 			kfree(buff);
 			break;
 		}
@@ -282,7 +288,7 @@ int ath11k_dbring_buffer_release_event(struct ath11k_base *ab,
 
 	srng = &ab->hal.srng_list[ring->refill_srng.ring_id];
 	num_entry = ev->fixed.num_buf_release_entry;
-	size = sizeof(*buff) + ring->buf_sz + ring->buf_align - 1;
+	size = ring->buf_sz + ring->buf_align - 1;
 	num_buff_reaped = 0;
 
 	spin_lock_bh(&srng->lock);
@@ -319,7 +325,8 @@ int ath11k_dbring_buffer_release_event(struct ath11k_base *ab,
 			ring->handler(ar, &handler_data);
 		}
 
-		memset(buff, 0, size);
+		buff->paddr = 0;
+		memset(buff->payload, 0, size);
 		ath11k_dbring_bufs_replenish(ar, ring, buff);
 	}
 
@@ -346,6 +353,7 @@ void ath11k_dbring_buf_cleanup(struct ath11k *ar, struct ath11k_dbring *ring)
 		idr_remove(&ring->bufs_idr, buf_id);
 		dma_unmap_single(ar->ab->dev, buff->paddr,
 				 ring->buf_sz, DMA_FROM_DEVICE);
+		kfree(buff->payload);
 		kfree(buff);
 	}
 

drivers/net/wireless/ath/ath11k/dbring.h

@@ -13,7 +13,7 @@
 
 struct ath11k_dbring_element {
 	dma_addr_t paddr;
-	u8 payload[0];
+	u8 *payload;
 };
 
 struct ath11k_dbring_data {