[PATCH 6.12 167/169] vsock/virtio: Allocate nonlinear SKBs for handling large transmit buffers

Greg Kroah-Hartman
2026-01-28T15:49:54Z

From: Will Deacon <will@kernel.org>

[Upstream commit 6693731487a8145a9b039bc983d77edc47693855]

When transmitting a vsock packet, virtio_transport_send_pkt_info() calls
virtio_transport_alloc_linear_skb() to allocate and fill SKBs with the
transmit data. Unfortunately, these are always linear allocations and
can therefore result in significant pressure on kmalloc() considering
that the maximum packet size (VIRTIO_VSOCK_MAX_PKT_BUF_SIZE +
VIRTIO_VSOCK_SKB_HEADROOM) is a little over 64KiB, resulting in a 128KiB
allocation for each packet.

Rework the vsock SKB allocation so that, for sizes with page order
greater than PAGE_ALLOC_COSTLY_ORDER, a nonlinear SKB is allocated
instead with the packet header in the SKB and the transmit data in the
fragments. Note that this affects both the vhost and virtio transports.

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>
Message-Id: <20250717090116.11987-10-will@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Heitor Alves de Siqueira <halves@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/vmw_vsock/virtio_transport_common.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -111,7 +111,8 @@ static int virtio_transport_fill_skb(str
&info->msg->msg_iter,
len);

- return memcpy_from_msg(skb_put(skb, len), info->msg, len);
+ virtio_vsock_skb_put(skb, len);
+ return skb_copy_datagram_from_iter(skb, 0, &info->msg->msg_iter, len);
}

static void virtio_transport_init_hdr(struct sk_buff *skb,
@@ -263,7 +264,7 @@ static struct sk_buff *virtio_transport_
if (!zcopy)
skb_len += payload_len;

- skb = virtio_vsock_alloc_linear_skb(skb_len, GFP_KERNEL);
+ skb = virtio_vsock_alloc_skb(skb_len, GFP_KERNEL);
if (!skb)
return NULL;