net/mlx5e: kTLS, Fix incorrect page refcounting

The kTLS tx handling code is using a mix of get_page() and
page_ref_inc() APIs to increment the page reference. But on the release
path (mlx5e_ktls_tx_handle_resync_dump_comp()), only put_page() is used.

This is an issue when using pages from large folios: the get_page()
references are stored on the folio page while the page_ref_inc()
references are stored directly in the given page. On release the folio
page will be dereferenced too many times.

This was found while doing kTLS testing with sendfile() + ZC when the
served file was read from NFS on a kernel with NFS large folios support
(commit 49b29a5 ("nfs: add support for large folios")).

Fixes: 84d1bb2 ("net/mlx5e: kTLS, Limit DUMP wqe size")
Signed-off-by: Dragos Tatulea <[email protected]>
Signed-off-by: Tariq Toukan <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: dtatulea

drivers/net/ethernet/mellanox/mlx5/core/en_accel/ktls_tx.c

@@ -660,7 +660,7 @@ tx_sync_info_get(struct mlx5e_ktls_offload_context_tx *priv_tx,
 	while (remaining > 0) {
 		skb_frag_t *frag = &record->frags[i];
 
-		get_page(skb_frag_page(frag));
+		page_ref_inc(skb_frag_page(frag));
 		remaining -= skb_frag_size(frag);
 		info->frags[i++] = *frag;
 	}
@@ -763,7 +763,7 @@ void mlx5e_ktls_tx_handle_resync_dump_comp(struct mlx5e_txqsq *sq,
 	stats = sq->stats;
 
 	mlx5e_tx_dma_unmap(sq->pdev, dma);
-	put_page(wi->resync_dump_frag_page);
+	page_ref_dec(wi->resync_dump_frag_page);
 	stats->tls_dump_packets++;
 	stats->tls_dump_bytes += wi->num_bytes;
 }
@@ -816,12 +816,12 @@ mlx5e_ktls_tx_handle_ooo(struct mlx5e_ktls_offload_context_tx *priv_tx,
 
 err_out:
 	for (; i < info.nr_frags; i++)
-		/* The put_page() here undoes the page ref obtained in tx_sync_info_get().
+		/* The page_ref_dec() here undoes the page ref obtained in tx_sync_info_get().
 		 * Page refs obtained for the DUMP WQEs above (by page_ref_add) will be
 		 * released only upon their completions (or in mlx5e_free_txqsq_descs,
 		 * if channel closes).
 		 */
-		put_page(skb_frag_page(&info.frags[i]));
+		page_ref_dec(skb_frag_page(&info.frags[i]));
 
 	return MLX5E_KTLS_SYNC_FAIL;
 }