Use page_pool for RX buffer allocation in mergeable and small buffer
modes to enable page recycling and avoid repeated page allocator calls.
skb_mark_for_recycle() enables page reuse in the network stack.

Big packets mode is unchanged because it uses page->private for linked
list chaining of multiple pages per buffer, which conflicts with
page_pool's internal use of page->private.

Implement conditional DMA premapping using virtqueue_dma_dev():
- When non-NULL (vhost, virtio-pci): use PP_FLAG_DMA_MAP with page_pool
  handling DMA mapping, submit via virtqueue_add_inbuf_premapped()
- When NULL (VDUSE, direct physical): page_pool handles allocation only,
  submit via virtqueue_add_inbuf_ctx()

This preserves the DMA premapping optimization from commit 31f3cd4e5756b
("virtio-net: rq submits premapped per-buffer") while adding page_pool
support as a prerequisite for future zero-copy features (devmem TCP,
io_uring ZCRX).

Page pools are created in probe and destroyed in remove (not open/close),
following existing driver behavior where RX buffers remain in virtqueues
across interface state changes.

Signed-off-by: Vishwanath Seshagiri <redacted>
---
Resend for net-next window (no changes from v7).
- v7:
  https://lore.kernel.org/virtualization/20260210014305.3236342-1-vishs@meta.com/ (local)

Changes in v7:
- Replace virtnet_put_page() helper with direct page_pool_put_page()
  calls (Xuan Zhuo)
- Add virtnet_no_page_pool() helper to consolidate big_packets mode check
  (Michael S. Tsirkin)
- Add DMA sync_for_cpu for subsequent buffers in xdp_linearize_page() when
  use_page_pool_dma is set (Michael S. Tsirkin)
- Remove unused pp_params.dev assignment in non-DMA path
- Add page pool recreation in virtnet_restore_up() for freeze/restore support (Chris Mason's
Review Prompt)
- v6:
  https://lore.kernel.org/virtualization/20260208175410.1910001-1-vishs@meta.com/ (local)

Changes in v6:
- Drop page_pool_frag_offset_add() helper and switch to page_pool_alloc_va();
  page_pool_alloc_netmem() already handles internal fragmentation internally
  (Jakub Kicinski)
- v5:
  https://lore.kernel.org/virtualization/20260206002715.1885869-1-vishs@meta.com/ (local)

Benchmark results:

Configuration: pktgen TX -> tap -> vhost-net | virtio-net RX -> XDP_DROP

Small packets (64 bytes, mrg_rxbuf=off):
  1Q:  853,493 -> 868,923 pps  (+1.8%)
  2Q: 1,655,793 -> 1,696,707 pps (+2.5%)
  4Q: 3,143,375 -> 3,302,511 pps (+5.1%)
  8Q: 6,082,590 -> 6,156,894 pps (+1.2%)

Mergeable RX (64 bytes):
  1Q:   766,168 ->   814,493 pps  (+6.3%)
  2Q: 1,384,871 -> 1,670,639 pps (+20.6%)
  4Q: 2,773,081 -> 3,080,574 pps (+11.1%)
  8Q: 5,600,615 -> 6,043,891 pps  (+7.9%)

Mergeable RX (1500 bytes):
  1Q:   741,579 ->   785,442 pps  (+5.9%)
  2Q: 1,310,043 -> 1,534,554 pps (+17.1%)
  4Q: 2,748,700 -> 2,890,582 pps  (+5.2%)
  8Q: 5,348,589 -> 5,618,664 pps  (+5.0%)

 drivers/net/Kconfig      |   1 +
 drivers/net/virtio_net.c | 467 ++++++++++++++++++++-------------------
 2 files changed, 243 insertions(+), 225 deletions(-)

diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index ac12eaf11755..f1e6b6b0a86f 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig

@@ -450,6 +450,7 @@ config VIRTIO_NET
 	depends on VIRTIO
 	select NET_FAILOVER
 	select DIMLIB
+	select PAGE_POOL
 	help
 	  This is the virtual network driver for virtio.  It can be used with
 	  QEMU based VMMs (like KVM or Xen).  Say Y or M.

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index db88dcaefb20..32aede2b1ed5 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -26,6 +26,7 @@
 #include <net/netdev_rx_queue.h>
 #include <net/netdev_queues.h>
 #include <net/xdp_sock_drv.h>
+#include <net/page_pool/helpers.h>

 static int napi_weight = NAPI_POLL_WEIGHT;
 module_param(napi_weight, int, 0444);

@@ -290,14 +291,6 @@ struct virtnet_interrupt_coalesce {
 	u32 max_usecs;
 };

-/* The dma information of pages allocated at a time. */
-struct virtnet_rq_dma {
-	dma_addr_t addr;
-	u32 ref;
-	u16 len;
-	u16 need_sync;
-};
-
 /* Internal representation of a send virtqueue */
 struct send_queue {
 	/* Virtqueue associated with this send _queue */

@@ -356,8 +349,10 @@ struct receive_queue {
 	/* Average packet length for mergeable receive buffers. */
 	struct ewma_pkt_len mrg_avg_pkt_len;

-	/* Page frag for packet buffer allocation. */
-	struct page_frag alloc_frag;
+	struct page_pool *page_pool;
+
+	/* True if page_pool handles DMA mapping via PP_FLAG_DMA_MAP */
+	bool use_page_pool_dma;

 	/* RX: fragments + linear part + virtio header */
 	struct scatterlist sg[MAX_SKB_FRAGS + 2];

@@ -370,9 +365,6 @@ struct receive_queue {

 	struct xdp_rxq_info xdp_rxq;

-	/* Record the last dma info to free after new pages is allocated. */
-	struct virtnet_rq_dma *last_dma;
-
 	struct xsk_buff_pool *xsk_pool;

 	/* xdp rxq used by xsk */

@@ -521,11 +513,14 @@ static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
 			       struct virtnet_rq_stats *stats);
 static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue *rq,
 				 struct sk_buff *skb, u8 flags);
-static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
+static struct sk_buff *virtnet_skb_append_frag(struct receive_queue *rq,
+					       struct sk_buff *head_skb,
 					       struct sk_buff *curr_skb,
 					       struct page *page, void *buf,
 					       int len, int truesize);
 static void virtnet_xsk_completed(struct send_queue *sq, int num);
+static void free_unused_bufs(struct virtnet_info *vi);
+static void virtnet_del_vqs(struct virtnet_info *vi);

 enum virtnet_xmit_type {
 	VIRTNET_XMIT_TYPE_SKB,

@@ -706,15 +701,18 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
 	return p;
 }

+static bool virtnet_no_page_pool(struct virtnet_info *vi)
+{

 err_buf:

@@ -2666,32 +2586,40 @@ static void receive_buf(struct virtnet_info *vi, struct receive_queue *rq,
 static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
 			     gfp_t gfp)
 {
-	char *buf;
 	unsigned int xdp_headroom = virtnet_get_headroom(vi);
 	void *ctx = (void *)(unsigned long)xdp_headroom;
-	int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
+	unsigned int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
+	struct page *page;
+	dma_addr_t addr;
+	char *buf;
 	int err;

 	len = SKB_DATA_ALIGN(len) +
 	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));

-	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
-		return -ENOMEM;
-
-	buf = virtnet_rq_alloc(rq, len, gfp);
+	buf = page_pool_alloc_va(rq->page_pool, &len, gfp);
 	if (unlikely(!buf))
 		return -ENOMEM;

 	buf += VIRTNET_RX_PAD + xdp_headroom;

-	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
+	if (rq->use_page_pool_dma) {
+		page = virt_to_head_page(buf);
+		addr = page_pool_get_dma_addr(page) +
+		       (buf - (char *)page_address(page));

-	err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1, buf, ctx, gfp);
-	if (err < 0) {
-		virtnet_rq_unmap(rq, buf, 0);
-		put_page(virt_to_head_page(buf));
+		sg_init_table(rq->sg, 1);
+		sg_fill_dma(rq->sg, addr, vi->hdr_len + GOOD_PACKET_LEN);
+		err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
+						    buf, ctx, gfp);
+	} else {
+		sg_init_one(rq->sg, buf, vi->hdr_len + GOOD_PACKET_LEN);
+		err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
+					      buf, ctx, gfp);
 	}