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vhost-net: fix TX stall when vhost owns virtio-net header

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When vhost owns the virtio-net header, i.e. when
VHOST_NET_F_VIRTIO_NET_HDR is negotiated, sock_hlen is 0,
meaning that no header will be forwarded to the TAP device.

In the current vhost_net_build_xdp() implementation,
when sock_hlen == 0, the gso pointer can point at the start of the
Ethernet frame instead of a virtio-net header.
This results in a wrong interpretation of the destination MAC address
bytes as struct virtio_net_hdr fields.

This can, for some MAC addresses, trigger -EINVAL and return early
before the TX descriptor is completed, which can stall vhost-net TX.

Before 97b2409f28, the gso pointer was set to the zeroed padding area,
using it as a synthetic virtio-net header. Restore that behavior.

Fixes: 97b2409f28 ("vhost-net: reduce one userspace copy when building XDP buff")
Signed-off-by: Enrico Zanda <enrico.zanda@arm.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://patch.msgid.link/20260708152242.2268848-1-enrico.zanda@arm.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Enrico Zanda 2026-07-08 16:22:42 +01:00 committed by Paolo Abeni
parent 91957b89da
commit 3c0d10f233
1 changed files with 5 additions and 3 deletions
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8
drivers/vhost/net.c
View File

@ -731,10 +731,12 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
goto err;
}
gso = buf + pad - sock_hlen;
if (!sock_hlen)
if (!sock_hlen) {
memset(buf, 0, pad);
gso = buf;
} else {
gso = buf + pad - sock_hlen;
}
if ((gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
vhost16_to_cpu(vq, gso->csum_start) +