Re: [PATCH net 4/4] virtio-net: allow more allocated space for mergeable XDP
From: Jason Wang <jasowang@redhat.com>
Date: 2025-06-26 02:51:16
Also in:
bpf, lkml, virtualization
On Thu, Jun 26, 2025 at 12:10 AM Bui Quang Minh [off-list ref] wrote:
When the mergeable receive buffer is prefilled before XDP is set, it does not reserve the space for XDP_PACKET_HEADROOM and skb_shared_info. So when XDP is set and this buffer is used to receive frame, we need to create a new buffer with reserved headroom, tailroom and copy the frame data over. Currently, the new buffer's size is restricted to PAGE_SIZE only. If the frame data's length + headroom + tailroom exceeds PAGE_SIZE, the frame is dropped. However, it seems like there is no restriction on the total size in XDP. So we can just increase the size of new buffer to 2 * PAGE_SIZE in that case and continue to process the frame. In my opinion, the current drop behavior is fine and expected so this commit is just an improvement not a bug fix.
Then this should go for net-next.
quoted hunk ↗ jump to hunk
Signed-off-by: Bui Quang Minh <redacted> --- drivers/net/virtio_net.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-)diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 844cb2a78be0..663cec686045 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c@@ -2277,13 +2277,26 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi, len); if (!xdp_page) return NULL; + + *frame_sz = PAGE_SIZE; } else { + unsigned int total_len; + xdp_room = SKB_DATA_ALIGN(XDP_PACKET_HEADROOM + sizeof(struct skb_shared_info)); - if (*len + xdp_room > PAGE_SIZE) + total_len = *len + xdp_room; + + /* This must never happen because len cannot exceed PAGE_SIZE */ + if (unlikely(total_len > 2 * PAGE_SIZE)) return NULL; - xdp_page = alloc_page(GFP_ATOMIC); + if (total_len > PAGE_SIZE) { + xdp_page = alloc_pages(GFP_ATOMIC, 1);
I'm not sure it's worth optimizing the corner case here that may bring burdens for maintenance. And a good optimization here is to reduce the logic duplication by reusing xdp_linearize_page().
quoted hunk ↗ jump to hunk
+ *frame_sz = 2 * PAGE_SIZE; + } else { + xdp_page = alloc_page(GFP_ATOMIC); + *frame_sz = PAGE_SIZE; + } if (!xdp_page) return NULL;@@ -2291,8 +2304,6 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi, page_address(*page) + offset, *len); } - *frame_sz = PAGE_SIZE; - put_page(*page); *page = xdp_page; --
Thanks
2.43.0