Hello, I noticed a regression from v.6.6.43 to v6.6.44 caused by this commit.

When using virtio NIC with a QEMU/KVM Windows guest, network traffic from the VM stalls in the outbound (upload) direction.This affects remote access and file shares most noticeably, and the inbound (download) direction does not have the issue.

iperf3 will show consistent results, 0 bytes/sec when initiating a test within the guest to a server on LAN, and reverse will be full speed. Nothing out of the ordinary in host dmesg or guest Event Viewer while the behavior is being displayed.

Crucially, this only seems to affect Windows guests, a Ubuntu guest with the same NIC configuration works fine in both directions. I wonder if NetKVM guest drivers may be related, the current latest version of the drivers (v248) did not make a difference, but it is several months old.

Let me know if there are any further tests or info I can provide, thanks!