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Message-ID: <20260205013640-mutt-send-email-mst@kernel.org>
Date: Thu, 5 Feb 2026 01:40:12 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Vishwanath Seshagiri <vishs@...a.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 net-next v4 1/2] virtio_net: add page_pool support for
buffer allocation
On Wed, Feb 04, 2026 at 10:34:38PM -0800, Vishwanath Seshagiri wrote:
>
>
> On 2/4/26 9:30 PM, Michael S. Tsirkin wrote:
> > On Wed, Feb 04, 2026 at 11:36:16AM -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>
> > > ---
> > > drivers/net/Kconfig | 1 +
> > > drivers/net/virtio_net.c | 351 ++++++++++++++++++++++-----------------
> > > 2 files changed, 201 insertions(+), 151 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..74c51e597c3f 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);
> > > @@ -359,6 +360,11 @@ struct receive_queue {
> > > /* 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];
> > > @@ -521,11 +527,13 @@ 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 +714,24 @@ 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);
> > > }
> > > static void enable_rx_mode_work(struct virtnet_info *vi)
> > > @@ -877,9 +894,12 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> > > if (unlikely(!skb))
> > > return NULL;
> > > - page = (struct page *)page->private;
> > > - if (page)
> > > - give_pages(rq, page);
> > > + if (!rq->page_pool) {
> >
> > I think this is ok because big_packets is exactly when this happens.
> > but it is confusing that the conditions on free and alloc are
> > written differently. A comment with an explanation, at least?
>
> I will add a comment here in v5.
Would be better to also unify the way we test on alloc and free paths,
if possible.
> >
> >
> > > + page = (struct page *)page->private;
> > > + if (page)
> > > + give_pages(rq, page);
> > > + }
> > > +
> > > goto ok;
> > > }
> > > @@ -925,7 +945,7 @@ 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;
> > > }
> > > @@ -965,93 +985,10 @@ static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
> > > 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);
> >
> > it gives me pause that this patch never does sync.
> > don't you need page_pool_dma_sync_for_cpu somewhere?
>
> I missed the page_pool_dma_sync_for_cpu in the receive path before
> reading the buffer data. I will add it in v5.
>
> >
> >
> >
> > > -
> > > - /* 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 +1004,6 @@ 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 +1269,7 @@ 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 +1705,7 @@ 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 +1715,7 @@ 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 +1807,7 @@ 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 +1831,7 @@ 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 +1839,21 @@ 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;
> > > }
> > > @@ -1996,7 +1930,7 @@ 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 +1962,15 @@ 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;
> > > }
> > > @@ -2082,12 +2018,14 @@ 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 +2080,7 @@ 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 +2191,7 @@ 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 +2210,7 @@ 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 +2275,7 @@ 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 +2285,7 @@ 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 +2331,8 @@ 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 +2343,10 @@ 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 +2354,8 @@ 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 +2387,7 @@ 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 {
> > > @@ -2499,6 +2440,8 @@ 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);
> > > if (unlikely(!buf)) {
> > > @@ -2517,7 +2460,7 @@ 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 +2470,7 @@ 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 +2609,42 @@ 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 offset;
> > > + 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);
> > > - if (unlikely(!buf))
> > > + page = page_pool_alloc_frag(rq->page_pool, &offset, len, gfp);
> > > + if (unlikely(!page))
> > > return -ENOMEM;
> > > + buf = page_address(page) + offset;
> > > 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) {
> > > + addr = page_pool_get_dma_addr(page) + offset;
> > > + addr += VIRTNET_RX_PAD + xdp_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));
> > > + 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 +2717,15 @@ 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 offset;
> > > + struct page *page;
> > > + dma_addr_t addr;
> > > char *buf;
> > > + void *ctx;
> > > int err;
> > > /* Extra tailroom is needed to satisfy XDP's assumption. This
> > > @@ -2779,18 +2734,14 @@ 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);
> > > - if (unlikely(!buf))
> > > + page = page_pool_alloc_frag(rq->page_pool, &offset, len + room, gfp);
> > > + if (unlikely(!page))
> > > return -ENOMEM;
> > > + buf = page_address(page) + offset;
> > > buf += headroom; /* advance address leaving hole at front of pkt */
> > > - hole = alloc_frag->size - alloc_frag->offset;
> > > +
> > > + hole = PAGE_SIZE - (offset + len + room);
> > > if (hole < len + room) {
> > > /* To avoid internal fragmentation, if there is very likely not
> > > * enough space for another buffer, add the remaining space to
> > > @@ -2800,18 +2751,27 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> > > */
> > > if (!headroom)
> > > len += hole;
> > > - alloc_frag->offset += hole;
> >
> > Hmm. All these allocations are tricky.
> > So we used to advance offset by hole but with page pool api
> > what advances pool->frag_offset? If nothing will not the next
> > small allocation reuse the space and overlap the buffer?
>
> I tested with debug tracing and confirmed the issue triggers with
> typical 1536-byte allocations. When len += hole extends the buffer into
> 3072-4096, page_pool's internal frag_offset stays at 3072, so a
> subsequent smaller allocation could overlap.
> Since page_pool manages frag_offset internally and there's no API to
> advance it past the hole, the fix is to remove the if (hole < len +
> room) block entirely.
Well... but this means that fragmentation can waste memory
which is not accounted for anywhere. Just add an API for this?
> >
> >
> > > }
> > > - virtnet_rq_init_one_sg(rq, buf, len);
> > > -
> > > 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) {
> > > + addr = page_pool_get_dma_addr(page) + offset;
> > > + addr += headroom;
> > > +
> > > + 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 +3088,10 @@ 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 +3131,81 @@ 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);
> > > @@ -6441,10 +6479,8 @@ 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 +6981,14 @@ 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 +7002,7 @@ 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;
> > > }
> > > }
> > > @@ -7075,7 +7119,10 @@ 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);
> > > @@ -7104,6 +7151,8 @@ static void remove_vq_common(struct virtnet_info *vi)
> > > free_receive_page_frags(vi);
> > > + virtnet_destroy_page_pools(vi);
> > > +
> > > virtnet_del_vqs(vi);
> > > }
> > > --
> > > 2.47.3
> >
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