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Message-ID: <3e6f368f-8c52-487c-816c-4dae13c70478@meta.com>
Date: Sun, 8 Feb 2026 10:56:15 -0800
From: Vishwanath Seshagiri <vishs@...a.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
Eugenio Pérez <eperezma@...hat.com>,
Andrew Lunn <andrew+netdev@...n.ch>,
"David S . Miller"
<davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, David Wei <dw@...idwei.uk>,
Matteo Croce <technoboy85@...il.com>,
Ilias Apalodimas <ilias.apalodimas@...aro.org>, netdev@...r.kernel.org,
virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
kernel-team@...a.com
Subject: Re: [PATCH v6] virtio_net: add page_pool support for buffer
allocation
On 2/8/26 10:42 AM, Michael S. Tsirkin wrote:
> On Sun, Feb 08, 2026 at 09:54:10AM -0800, Vishwanath Seshagiri wrote:
>> 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 <vishs@...a.com>
>> ---
>> 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/
>>
>> 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 | 434 +++++++++++++++++++--------------------
>> 2 files changed, 217 insertions(+), 218 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..5055df56e4a7 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 +513,13 @@ 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);
>>
>> enum virtnet_xmit_type {
>> VIRTNET_XMIT_TYPE_SKB,
>> @@ -706,15 +700,24 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
>> return p;
>> }
>>
>> +static void virtnet_put_page(struct receive_queue *rq, struct page *page,
>> + bool allow_direct)
>> +{
>> + if (page_pool_page_is_pp(page))
>> + page_pool_put_page(rq->page_pool, page, -1, allow_direct);
>> + else
>> + put_page(page);
>> +}
>> +
>> static void virtnet_rq_free_buf(struct virtnet_info *vi,
>> struct receive_queue *rq, void *buf)
>> {
>> if (vi->mergeable_rx_bufs)
>> - put_page(virt_to_head_page(buf));
>> + virtnet_put_page(rq, virt_to_head_page(buf), false);
>> else if (vi->big_packets)
>> give_pages(rq, buf);
>> else
>> - put_page(virt_to_head_page(buf));
>> + virtnet_put_page(rq, virt_to_head_page(buf), false);
>
> equivalently:
>
> if (vi->big_packets && !vi->mergeable_rx_bufs)
> give_pages(rq, buf);
> else
> virtnet_put_page(rq, virt_to_head_page(buf), false);
>
> and then it matches the check we have like in 10 places in
> this file.
>
> maybe it's time for a helper that does vi->big_packets &&
> !vi->mergeable_rx_bufs?
>
> maybe virtnet_no_page_pool()?
Good idea. I will create the virtnet_no_page_pool() api and use
that for making intent clear.
>
>
>
>
>> }
>>
>> static void enable_rx_mode_work(struct virtnet_info *vi)
>> @@ -876,10 +879,16 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>> skb = virtnet_build_skb(buf, truesize, p - buf, len);
>> if (unlikely(!skb))
>> return NULL;
>> + /* Big packets mode chains pages via page->private, which is
>> + * incompatible with the way page_pool uses page->private.
>> + * Currently, big packets mode doesn't use page pools.
>> + */
>> + if (vi->big_packets && !vi->mergeable_rx_bufs) {
>> + page = (struct page *)page->private;
>> + if (page)
>> + give_pages(rq, page);
>> + }
>>
>> - page = (struct page *)page->private;
>> - if (page)
>> - give_pages(rq, page);
>> goto ok;
>> }
>>
>> @@ -925,133 +934,18 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>> hdr = skb_vnet_common_hdr(skb);
>> memcpy(hdr, hdr_p, hdr_len);
>> if (page_to_free)
>> - put_page(page_to_free);
>> + virtnet_put_page(rq, page_to_free, true);
>>
>> return skb;
>> }
>>
>> -static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
>> -{
>> - struct virtnet_info *vi = rq->vq->vdev->priv;
>> - struct page *page = virt_to_head_page(buf);
>> - struct virtnet_rq_dma *dma;
>> - void *head;
>> - int offset;
>> -
>> - BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>> -
>> - head = page_address(page);
>> -
>> - dma = head;
>> -
>> - --dma->ref;
>> -
>> - if (dma->need_sync && len) {
>> - offset = buf - (head + sizeof(*dma));
>> -
>> - virtqueue_map_sync_single_range_for_cpu(rq->vq, dma->addr,
>> - offset, len,
>> - DMA_FROM_DEVICE);
>> - }
>> -
>> - if (dma->ref)
>> - return;
>> -
>> - virtqueue_unmap_single_attrs(rq->vq, dma->addr, dma->len,
>> - DMA_FROM_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
>> - put_page(page);
>> -}
>> -
>> static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
>> {
>> struct virtnet_info *vi = rq->vq->vdev->priv;
>> - void *buf;
>>
>> BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>>
>> - buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
>> - if (buf)
>> - virtnet_rq_unmap(rq, buf, *len);
>> -
>> - return buf;
>> -}
>> -
>> -static void virtnet_rq_init_one_sg(struct receive_queue *rq, void *buf, u32 len)
>> -{
>> - struct virtnet_info *vi = rq->vq->vdev->priv;
>> - struct virtnet_rq_dma *dma;
>> - dma_addr_t addr;
>> - u32 offset;
>> - void *head;
>> -
>> - BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>> -
>> - head = page_address(rq->alloc_frag.page);
>> -
>> - offset = buf - head;
>> -
>> - dma = head;
>> -
>> - addr = dma->addr - sizeof(*dma) + offset;
>> -
>> - sg_init_table(rq->sg, 1);
>> - sg_fill_dma(rq->sg, addr, len);
>> -}
>> -
>> -static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
>> -{
>> - struct page_frag *alloc_frag = &rq->alloc_frag;
>> - struct virtnet_info *vi = rq->vq->vdev->priv;
>> - struct virtnet_rq_dma *dma;
>> - void *buf, *head;
>> - dma_addr_t addr;
>> -
>> - BUG_ON(vi->big_packets && !vi->mergeable_rx_bufs);
>> -
>> - head = page_address(alloc_frag->page);
>> -
>> - dma = head;
>> -
>> - /* new pages */
>> - if (!alloc_frag->offset) {
>> - if (rq->last_dma) {
>> - /* Now, the new page is allocated, the last dma
>> - * will not be used. So the dma can be unmapped
>> - * if the ref is 0.
>> - */
>> - virtnet_rq_unmap(rq, rq->last_dma, 0);
>> - rq->last_dma = NULL;
>> - }
>> -
>> - dma->len = alloc_frag->size - sizeof(*dma);
>> -
>> - addr = virtqueue_map_single_attrs(rq->vq, dma + 1,
>> - dma->len, DMA_FROM_DEVICE, 0);
>> - if (virtqueue_map_mapping_error(rq->vq, addr))
>> - return NULL;
>> -
>> - dma->addr = addr;
>> - dma->need_sync = virtqueue_map_need_sync(rq->vq, addr);
>> -
>> - /* Add a reference to dma to prevent the entire dma from
>> - * being released during error handling. This reference
>> - * will be freed after the pages are no longer used.
>> - */
>> - get_page(alloc_frag->page);
>> - dma->ref = 1;
>> - alloc_frag->offset = sizeof(*dma);
>> -
>> - rq->last_dma = dma;
>> - }
>> -
>> - ++dma->ref;
>> -
>> - buf = head + alloc_frag->offset;
>> -
>> - get_page(alloc_frag->page);
>> - alloc_frag->offset += size;
>> -
>> - return buf;
>> + return virtqueue_get_buf_ctx(rq->vq, len, ctx);
>> }
>>
>> static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
>> @@ -1067,9 +961,6 @@ static void virtnet_rq_unmap_free_buf(struct virtqueue *vq, void *buf)
>> return;
>> }
>>
>> - if (!vi->big_packets || vi->mergeable_rx_bufs)
>> - virtnet_rq_unmap(rq, buf, 0);
>> -
>> virtnet_rq_free_buf(vi, rq, buf);
>> }
>>
>> @@ -1335,7 +1226,7 @@ static int xsk_append_merge_buffer(struct virtnet_info *vi,
>>
>> truesize = len;
>>
>> - curr_skb = virtnet_skb_append_frag(head_skb, curr_skb, page,
>> + curr_skb = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
>> buf, len, truesize);
>> if (!curr_skb) {
>> put_page(page);
>> @@ -1771,7 +1662,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>> return ret;
>> }
>>
>> -static void put_xdp_frags(struct xdp_buff *xdp)
>> +static void put_xdp_frags(struct receive_queue *rq, struct xdp_buff *xdp)
>> {
>> struct skb_shared_info *shinfo;
>> struct page *xdp_page;
>> @@ -1781,7 +1672,7 @@ static void put_xdp_frags(struct xdp_buff *xdp)
>> shinfo = xdp_get_shared_info_from_buff(xdp);
>> for (i = 0; i < shinfo->nr_frags; i++) {
>> xdp_page = skb_frag_page(&shinfo->frags[i]);
>> - put_page(xdp_page);
>> + virtnet_put_page(rq, xdp_page, true);
>> }
>> }
>> }
>> @@ -1873,7 +1764,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>> if (page_off + *len + tailroom > PAGE_SIZE)
>> return NULL;
>>
>> - page = alloc_page(GFP_ATOMIC);
>> + page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
>> if (!page)
>> return NULL;
>>
>> @@ -1897,7 +1788,7 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>> off = buf - page_address(p);
>>
>> if (check_mergeable_len(dev, ctx, buflen)) {
>> - put_page(p);
>> + virtnet_put_page(rq, p, true);
>> goto err_buf;
>> }
>>
>> @@ -1905,21 +1796,21 @@ static struct page *xdp_linearize_page(struct net_device *dev,
>> * is sending packet larger than the MTU.
>> */
>> if ((page_off + buflen + tailroom) > PAGE_SIZE) {
>> - put_page(p);
>> + virtnet_put_page(rq, p, true);
>> goto err_buf;
>> }
>>
>> memcpy(page_address(page) + page_off,
>> page_address(p) + off, buflen);
>> page_off += buflen;
>> - put_page(p);
>> + virtnet_put_page(rq, p, true);
>> }
>>
>> /* Headroom does not contribute to packet length */
>> *len = page_off - XDP_PACKET_HEADROOM;
>> return page;
>> err_buf:
>> - __free_pages(page, 0);
>> + page_pool_put_page(rq->page_pool, page, -1, true);
>> return NULL;
>> }
>>
>> @@ -1969,6 +1860,12 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>> unsigned int metasize = 0;
>> u32 act;
>>
>> + if (rq->use_page_pool_dma) {
>> + int off = buf - page_address(page);
>> +
>> + page_pool_dma_sync_for_cpu(rq->page_pool, page, off, len);
>> + }
>> +
>
> hmm no this is wrong i think:
>
> struct virtio_net_hdr_mrg_rxbuf *hdr = buf + header_offset;
> int off = buf - page_address(page);
>
> you should sync from hdr not from buf.
>
Yeah, the sync offset should be from where device actually writes. I
will add change it in v7.
>
>
> besides did not receive_small already sync?
> we do not need two syncs.
Yes, 2 syncs are redundant. I will keep it in receive_small, so that
two syncs do not happen.
>
>
>
>
>> if (unlikely(hdr->hdr.gso_type))
>> goto err_xdp;
>>
>> @@ -1996,7 +1893,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>> goto err_xdp;
>>
>> buf = page_address(xdp_page);
>> - put_page(page);
>> + virtnet_put_page(rq, page, true);
>> page = xdp_page;
>> }
>>
>> @@ -2028,13 +1925,15 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>> if (metasize)
>> skb_metadata_set(skb, metasize);
>>
>> + skb_mark_for_recycle(skb);
>> +
>> return skb;
>>
>> err_xdp:
>> u64_stats_inc(&stats->xdp_drops);
>> err:
>> u64_stats_inc(&stats->drops);
>> - put_page(page);
>> + virtnet_put_page(rq, page, true);
>> xdp_xmit:
>> return NULL;
>> }
>> @@ -2056,6 +1955,12 @@ static struct sk_buff *receive_small(struct net_device *dev,
>> */
>> buf -= VIRTNET_RX_PAD + xdp_headroom;
>>
>> + if (rq->use_page_pool_dma) {
>> + int offset = buf - page_address(page);
>> +
>> + page_pool_dma_sync_for_cpu(rq->page_pool, page, offset, len);
>> + }
>
>
> similar issue I think. off by header len.
ack. will change it in v7.
>
>> +
>> len -= vi->hdr_len;
>> u64_stats_add(&stats->bytes, len);
>>
>> @@ -2082,12 +1987,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
>> }
>>
>> skb = receive_small_build_skb(vi, xdp_headroom, buf, len);
>> - if (likely(skb))
>> + if (likely(skb)) {
>> + skb_mark_for_recycle(skb);
>> return skb;
>> + }
>>
>> err:
>> u64_stats_inc(&stats->drops);
>> - put_page(page);
>> + virtnet_put_page(rq, page, true);
>> return NULL;
>> }
>>
>> @@ -2142,7 +2049,7 @@ static void mergeable_buf_free(struct receive_queue *rq, int num_buf,
>> }
>> u64_stats_add(&stats->bytes, len);
>> page = virt_to_head_page(buf);
>> - put_page(page);
>> + virtnet_put_page(rq, page, true);
>> }
>> }
>>
>> @@ -2253,7 +2160,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>> offset = buf - page_address(page);
>>
>> if (check_mergeable_len(dev, ctx, len)) {
>> - put_page(page);
>> + virtnet_put_page(rq, page, true);
>> goto err;
>> }
>>
>> @@ -2272,7 +2179,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
>> return 0;
>>
>> err:
>> - put_xdp_frags(xdp);
>> + put_xdp_frags(rq, xdp);
>> return -EINVAL;
>> }
>>
>> @@ -2337,7 +2244,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>> if (*len + xdp_room > PAGE_SIZE)
>> return NULL;
>>
>> - xdp_page = alloc_page(GFP_ATOMIC);
>> + xdp_page = page_pool_alloc_pages(rq->page_pool, GFP_ATOMIC);
>> if (!xdp_page)
>> return NULL;
>>
>> @@ -2347,7 +2254,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>>
>> *frame_sz = PAGE_SIZE;
>>
>> - put_page(*page);
>> + virtnet_put_page(rq, *page, true);
>>
>> *page = xdp_page;
>>
>> @@ -2393,6 +2300,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>> head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
>> if (unlikely(!head_skb))
>> break;
>> +
>> + skb_mark_for_recycle(head_skb);
>> return head_skb;
>>
>> case XDP_TX:
>> @@ -2403,10 +2312,10 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>> break;
>> }
>>
>> - put_xdp_frags(&xdp);
>> + put_xdp_frags(rq, &xdp);
>>
>> err_xdp:
>> - put_page(page);
>> + virtnet_put_page(rq, page, true);
>> mergeable_buf_free(rq, num_buf, dev, stats);
>>
>> u64_stats_inc(&stats->xdp_drops);
>> @@ -2414,7 +2323,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>> return NULL;
>> }
>>
>> -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)
>> @@ -2446,7 +2356,7 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
>>
>> offset = buf - page_address(page);
>> if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
>> - put_page(page);
>> + virtnet_put_page(rq, page, true);
>> skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
>> len, truesize);
>> } else {
>> @@ -2475,6 +2385,10 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>> unsigned int headroom = mergeable_ctx_to_headroom(ctx);
>>
>> head_skb = NULL;
>> +
>> + if (rq->use_page_pool_dma)
>> + page_pool_dma_sync_for_cpu(rq->page_pool, page, offset, len);
>> +
>
> nice but where is the sync for reset of buffers?
>
>> u64_stats_add(&stats->bytes, len - vi->hdr_len);
>>
>> if (check_mergeable_len(dev, ctx, len))
>> @@ -2499,6 +2413,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>>
>> if (unlikely(!curr_skb))
>> goto err_skb;
>> +
>> + skb_mark_for_recycle(head_skb);
>> while (--num_buf) {
>> buf = virtnet_rq_get_buf(rq, &len, &ctx);
>
> ok so we have recycling.
> I *think* that since below you set PP_FLAG_DMA_MAP, then page_pool does
> not sync_for_device on recycle;
> so CPU can write into packet data (e.g. XDP_PASS) and leave dirty cachelines.
> After reuse, on non-coherent DMA that can corrupt later packets unless you add
> PP_FLAG_DMA_SYNC_DEV (with max_len/offset) or do an explicit
> dma_sync_for_device before requeue.
>
>
> See Documentation/core-api/dma-api-howto.rst
>
> I agree it's annoying since maybe we did not touch it at all.
>
Right. I initially left it out since dma_sync_for_device is a no-op on
coherent platforms where virtio-net is typically deployed, but it's
needed for correctness on non-coherent architectures. Will add
PP_FLAG_DMA_SYNC_DEV with appropriate max_len/offset in v7.
>
>
>
>> if (unlikely(!buf)) {
>> @@ -2517,7 +2433,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>> goto err_skb;
>>
>> truesize = mergeable_ctx_to_truesize(ctx);
>> - curr_skb = virtnet_skb_append_frag(head_skb, curr_skb, page,
>> + curr_skb = virtnet_skb_append_frag(rq, head_skb, curr_skb, page,
>> buf, len, truesize);
>> if (!curr_skb)
>> goto err_skb;
>> @@ -2527,7 +2443,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>> return head_skb;
>>
>> err_skb:
>> - put_page(page);
>> + virtnet_put_page(rq, page, true);
>> mergeable_buf_free(rq, num_buf, dev, stats);
>>
>> err_buf:
>> @@ -2666,32 +2582,41 @@ 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);
>> }
>>
>> + if (err < 0)
>> + page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
>> + -1, false);
>> return err;
>> }
>>
>> @@ -2764,13 +2689,14 @@ static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
>> static int add_recvbuf_mergeable(struct virtnet_info *vi,
>> struct receive_queue *rq, gfp_t gfp)
>> {
>> - struct page_frag *alloc_frag = &rq->alloc_frag;
>> unsigned int headroom = virtnet_get_headroom(vi);
>> unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
>> unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
>> - unsigned int len, hole;
>> - void *ctx;
>> + unsigned int len, alloc_len;
>> + struct page *page;
>> + dma_addr_t addr;
>> char *buf;
>> + void *ctx;
>> int err;
>>
>> /* Extra tailroom is needed to satisfy XDP's assumption. This
>> @@ -2779,39 +2705,36 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>> */
>> len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
>>
>> - if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
>> - return -ENOMEM;
>> -
>> - if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
>> - len -= sizeof(struct virtnet_rq_dma);
>> -
>> - buf = virtnet_rq_alloc(rq, len + room, gfp);
>> + alloc_len = len + room;
>> + buf = page_pool_alloc_va(rq->page_pool, &alloc_len, gfp);
>> if (unlikely(!buf))
>> return -ENOMEM;
>>
>> buf += headroom; /* advance address leaving hole at front of pkt */
>> - hole = alloc_frag->size - alloc_frag->offset;
>> - if (hole < len + room) {
>> - /* To avoid internal fragmentation, if there is very likely not
>> - * enough space for another buffer, add the remaining space to
>> - * the current buffer.
>> - * XDP core assumes that frame_size of xdp_buff and the length
>> - * of the frag are PAGE_SIZE, so we disable the hole mechanism.
>> - */
>> - if (!headroom)
>> - len += hole;
>> - alloc_frag->offset += hole;
>> - }
>>
>> - virtnet_rq_init_one_sg(rq, buf, len);
>> + if (!headroom)
>> + len = alloc_len - room;
>>
>> ctx = mergeable_len_to_ctx(len + room, headroom);
>> - 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));
>> +
>> + if (rq->use_page_pool_dma) {
>> + page = virt_to_head_page(buf);
>> + addr = page_pool_get_dma_addr(page) +
>> + (buf - (char *)page_address(page));
>> +
>> + sg_init_table(rq->sg, 1);
>> + sg_fill_dma(rq->sg, addr, len);
>> + err = virtqueue_add_inbuf_premapped(rq->vq, rq->sg, 1,
>> + buf, ctx, gfp);
>> + } else {
>> + sg_init_one(rq->sg, buf, len);
>> + err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1,
>> + buf, ctx, gfp);
>> }
>>
>> + if (err < 0)
>> + page_pool_put_page(rq->page_pool, virt_to_head_page(buf),
>> + -1, false);
>> return err;
>> }
>>
>> @@ -3128,7 +3051,10 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
>> return err;
>>
>> err = xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xdp_rxq,
>> - MEM_TYPE_PAGE_SHARED, NULL);
>> + vi->rq[qp_index].page_pool ?
>> + MEM_TYPE_PAGE_POOL :
>> + MEM_TYPE_PAGE_SHARED,
>> + vi->rq[qp_index].page_pool);
>> if (err < 0)
>> goto err_xdp_reg_mem_model;
>>
>> @@ -3168,6 +3094,81 @@ static void virtnet_update_settings(struct virtnet_info *vi)
>> vi->duplex = duplex;
>> }
>>
>> +static int virtnet_create_page_pools(struct virtnet_info *vi)
>> +{
>> + int i, err;
>> +
>> + if (!vi->mergeable_rx_bufs && vi->big_packets)
>> + return 0;
>> +
>> + for (i = 0; i < vi->max_queue_pairs; i++) {
>> + struct receive_queue *rq = &vi->rq[i];
>> + struct page_pool_params pp_params = { 0 };
>> + struct device *dma_dev;
>> +
>> + if (rq->page_pool)
>> + continue;
>> +
>> + if (rq->xsk_pool)
>> + continue;
>> +
>> + pp_params.order = 0;
>> + pp_params.pool_size = virtqueue_get_vring_size(rq->vq);
>> + pp_params.nid = dev_to_node(vi->vdev->dev.parent);
>> + pp_params.netdev = vi->dev;
>> + pp_params.napi = &rq->napi;
>> +
>> + /* Check if backend supports DMA API (e.g., vhost, virtio-pci).
>> + * If so, use page_pool's DMA mapping for premapped buffers.
>> + * Otherwise (e.g., VDUSE), page_pool only handles allocation.
>> + */
>> + dma_dev = virtqueue_dma_dev(rq->vq);
>> + if (dma_dev) {
>> + pp_params.dev = dma_dev;
>> + pp_params.flags = PP_FLAG_DMA_MAP;
>> + pp_params.dma_dir = DMA_FROM_DEVICE;
>> + rq->use_page_pool_dma = true;
>> + } else {
>> + pp_params.dev = vi->vdev->dev.parent;
>> + pp_params.flags = 0;
>> + rq->use_page_pool_dma = false;
>> + }
>> +
>> + rq->page_pool = page_pool_create(&pp_params);
>> + if (IS_ERR(rq->page_pool)) {
>> + err = PTR_ERR(rq->page_pool);
>> + rq->page_pool = NULL;
>> + goto err_cleanup;
>> + }
>> + }
>> + return 0;
>> +
>> +err_cleanup:
>> + while (--i >= 0) {
>> + struct receive_queue *rq = &vi->rq[i];
>> +
>> + if (rq->page_pool) {
>> + page_pool_destroy(rq->page_pool);
>> + rq->page_pool = NULL;
>> + }
>> + }
>> + return err;
>> +}
>> +
>> +static void virtnet_destroy_page_pools(struct virtnet_info *vi)
>> +{
>> + int i;
>> +
>> + for (i = 0; i < vi->max_queue_pairs; i++) {
>> + struct receive_queue *rq = &vi->rq[i];
>> +
>> + if (rq->page_pool) {
>> + page_pool_destroy(rq->page_pool);
>> + rq->page_pool = NULL;
>> + }
>> + }
>> +}
>> +
>> static int virtnet_open(struct net_device *dev)
>> {
>> struct virtnet_info *vi = netdev_priv(dev);
>> @@ -6287,17 +6288,6 @@ static void free_receive_bufs(struct virtnet_info *vi)
>> rtnl_unlock();
>> }
>>
>> -static void free_receive_page_frags(struct virtnet_info *vi)
>> -{
>> - int i;
>> - for (i = 0; i < vi->max_queue_pairs; i++)
>> - if (vi->rq[i].alloc_frag.page) {
>> - if (vi->rq[i].last_dma)
>> - virtnet_rq_unmap(&vi->rq[i], vi->rq[i].last_dma, 0);
>> - put_page(vi->rq[i].alloc_frag.page);
>> - }
>> -}
>> -
>> static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf)
>> {
>> struct virtnet_info *vi = vq->vdev->priv;
>> @@ -6441,10 +6431,8 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
>> vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
>> vi->sq[i].vq = vqs[txq2vq(i)];
>> }
>> -
>> /* run here: ret == 0. */
>>
>> -
>> err_find:
>> kfree(ctx);
>> err_ctx:
>> @@ -6945,6 +6933,14 @@ static int virtnet_probe(struct virtio_device *vdev)
>> goto free;
>> }
>>
>> + /* Create page pools for receive queues.
>> + * Page pools are created at probe time so they can be used
>> + * with premapped DMA addresses throughout the device lifetime.
>> + */
>> + err = virtnet_create_page_pools(vi);
>> + if (err)
>> + goto free_irq_moder;
>> +
>> #ifdef CONFIG_SYSFS
>> if (vi->mergeable_rx_bufs)
>> dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;
>> @@ -6958,7 +6954,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>> vi->failover = net_failover_create(vi->dev);
>> if (IS_ERR(vi->failover)) {
>> err = PTR_ERR(vi->failover);
>> - goto free_vqs;
>> + goto free_page_pools;
>> }
>> }
>>
>> @@ -7075,9 +7071,11 @@ static int virtnet_probe(struct virtio_device *vdev)
>> unregister_netdev(dev);
>> free_failover:
>> net_failover_destroy(vi->failover);
>> -free_vqs:
>> +free_page_pools:
>> + virtnet_destroy_page_pools(vi);
>> +free_irq_moder:
>> + virtnet_free_irq_moder(vi);
>> virtio_reset_device(vdev);
>> - free_receive_page_frags(vi);
>> virtnet_del_vqs(vi);
>> free:
>> free_netdev(dev);
>> @@ -7102,7 +7100,7 @@ static void remove_vq_common(struct virtnet_info *vi)
>>
>> free_receive_bufs(vi);
>>
>> - free_receive_page_frags(vi);
>> + virtnet_destroy_page_pools(vi);
>>
>> virtnet_del_vqs(vi);
>> }
>> --
>> 2.47.3
>
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