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Message-ID: <87479293-96c9-4560-b7d7-c3ea6b10d9d9@meta.com>
Date: Sun, 8 Feb 2026 12:40:29 -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 11:05 AM, Michael S. Tsirkin wrote:
> On Sun, Feb 08, 2026 at 10:56:15AM -0800, Vishwanath Seshagiri wrote:
>> 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.
>
>
> erm. pls document assumptions like this in the future.
ack. will add these assumptions it into 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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