FAILED: patch "[PATCH] net: mana: Sync page pool RX frags for CPU" failed to apply to 6.18-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x c72a0f09c57f92113df69f9b902d11c9e4b132f5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026072020-cathedral-preoccupy-0b9c@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c72a0f09c57f92113df69f9b902d11c9e4b132f5 Mon Sep 17 00:00:00 2001
From: Dexuan Cui <decui@microsoft.com>
Date: Wed, 1 Jul 2026 21:12:37 -0700
Subject: [PATCH] net: mana: Sync page pool RX frags for CPU

MANA allocates RX buffers from page pool fragments when frag_count is
greater than 1. In that case the buffers remain DMA mapped by page pool
and the RX completion path does not call dma_unmap_single(). As a result,
the implicit sync-for-CPU normally performed by dma_unmap_single() is
missing before the packet data is passed to the networking stack.

This breaks RX on configurations which require explicit DMA syncing, for
example when booted with swiotlb=force.

Fix this by recording the page pool page and DMA sync offset when the RX
buffer is allocated, and syncing the received packet range for CPU access
before handing the RX buffer to the stack.

Fixes: 730ff06d3f5c ("net: mana: Use page pool fragments for RX buffers instead of full pages to improve memory efficiency.")
Cc: stable@vger.kernel.org
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Link: https://patch.msgid.link/20260702041237.617719-3-decui@microsoft.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
index dd4d1c0c582e..9d9bfd116dab 100644
--- a/drivers/net/ethernet/microsoft/mana/mana_en.c
+++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
@@ -2120,12 +2120,16 @@ static void mana_rx_skb(void *buf_va, bool from_pool,
 }
 
 static void *mana_get_rxfrag(struct mana_rxq *rxq, struct device *dev,
-			     dma_addr_t *da, bool *from_pool)
+			     dma_addr_t *da, bool *from_pool,
+			     struct page **pp_page, u32 *dma_sync_offset)
 {
 	struct page *page;
 	u32 offset;
 	void *va;
+
 	*from_pool = false;
+	*pp_page = NULL;
+	*dma_sync_offset = 0;
 
 	/* Don't use fragments for jumbo frames or XDP where it's 1 fragment
 	 * per page.
@@ -2163,31 +2167,47 @@ static void *mana_get_rxfrag(struct mana_rxq *rxq, struct device *dev,
 	va  = page_to_virt(page) + offset;
 	*da = page_pool_get_dma_addr(page) + offset + rxq->headroom;
 	*from_pool = true;
+	*pp_page = page;
+	*dma_sync_offset = offset + rxq->headroom;
 
 	return va;
 }
 
 /* Allocate frag for rx buffer, and save the old buf */
 static void mana_refill_rx_oob(struct device *dev, struct mana_rxq *rxq,
-			       struct mana_recv_buf_oob *rxoob, void **old_buf,
-			       bool *old_fp)
+			       struct mana_recv_buf_oob *rxoob, u32 pktlen,
+			       void **old_buf, bool *old_fp)
 {
+	struct page *pp_page;
+	u32 dma_sync_offset;
 	bool from_pool;
 	dma_addr_t da;
 	void *va;
 
-	va = mana_get_rxfrag(rxq, dev, &da, &from_pool);
+	va = mana_get_rxfrag(rxq, dev, &da, &from_pool, &pp_page,
+			     &dma_sync_offset);
 	if (!va)
 		return;
-	if (!rxoob->from_pool || rxq->frag_count == 1)
+	if (!rxoob->from_pool || rxq->frag_count == 1) {
 		dma_unmap_single(dev, rxoob->sgl[0].address, rxq->datasize,
 				 DMA_FROM_DEVICE);
+	} else {
+		/* The page pool maps the whole page and only syncs for device
+		 * automatically (PP_FLAG_DMA_SYNC_DEV). Sync the received bytes
+		 * for the CPU before they are read: this is required if DMA
+		 * is incoherent or bounce buffers are used.
+		 */
+		page_pool_dma_sync_for_cpu(rxq->page_pool, rxoob->pp_page,
+					   rxoob->dma_sync_offset, pktlen);
+	}
 	*old_buf = rxoob->buf_va;
 	*old_fp = rxoob->from_pool;
 
 	rxoob->buf_va = va;
 	rxoob->sgl[0].address = da;
 	rxoob->from_pool = from_pool;
+	rxoob->pp_page = pp_page;
+	rxoob->dma_sync_offset = dma_sync_offset;
 }
 
 static void mana_process_rx_cqe(struct mana_rxq *rxq, struct mana_cq *cq,
@@ -2258,7 +2278,8 @@ static void mana_process_rx_cqe(struct mana_rxq *rxq, struct mana_cq *cq,
 			/* Reuse the RX buffer since rxbuf_oob is unchanged. */
 		} else {
 
-			mana_refill_rx_oob(dev, rxq, rxbuf_oob, &old_buf, &old_fp);
+			mana_refill_rx_oob(dev, rxq, rxbuf_oob, pktlen,
+					   &old_buf, &old_fp);
 
 			/* Unsuccessful refill will have old_buf == NULL.
 			 * In this case, mana_rx_skb() will drop the packet.
@@ -2668,6 +2689,8 @@ static int mana_fill_rx_oob(struct mana_recv_buf_oob *rx_oob, u32 mem_key,
 			    struct mana_rxq *rxq, struct device *dev)
 {
 	struct mana_port_context *mpc = netdev_priv(rxq->ndev);
+	struct page *pp_page = NULL;
+	u32 dma_sync_offset = 0;
 	bool from_pool = false;
 	dma_addr_t da;
 	void *va;
@@ -2675,13 +2698,16 @@ static int mana_fill_rx_oob(struct mana_recv_buf_oob *rx_oob, u32 mem_key,
 	if (mpc->rxbufs_pre)
 		va = mana_get_rxbuf_pre(rxq, &da);
 	else
-		va = mana_get_rxfrag(rxq, dev, &da, &from_pool);
+		va = mana_get_rxfrag(rxq, dev, &da, &from_pool, &pp_page,
+				     &dma_sync_offset);
 
 	if (!va)
 		return -ENOMEM;
 
 	rx_oob->buf_va = va;
 	rx_oob->from_pool = from_pool;
+	rx_oob->pp_page = pp_page;
+	rx_oob->dma_sync_offset = dma_sync_offset;
 
 	rx_oob->sgl[0].address = da;
 	rx_oob->sgl[0].size = rxq->datasize;
diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
index 13c87baf018e..04acb6791dbd 100644
--- a/include/net/mana/mana.h
+++ b/include/net/mana/mana.h
@@ -305,6 +305,14 @@ struct mana_recv_buf_oob {
 
 	void *buf_va;
 	bool from_pool; /* allocated from a page pool */
+	/* head page of the page_pool fragment; valid only when
+	 * from_pool && frag_count > 1.
+	 */
+	struct page *pp_page;
+	/* Fragment offset plus rxq->headroom, passed to
+	 * page_pool_dma_sync_for_cpu().
+	 */
+	u32 dma_sync_offset;
 
 	/* SGL of the buffer going to be sent as part of the work request. */
 	u32 num_sge;