Re: [PATCH v3 3/3] selftests: net: add a virtio_net deadlock selftest

[Bui Quang Minh <minhquangbui99@gmail.com>]

On 4/16/25 11:27, Jakub Kicinski wrote:
> On Tue, 15 Apr 2025 14:43:41 +0700 Bui Quang Minh wrote:
>> +def setup_xsk(cfg, xdp_queue_id = 0) -> bkg:
>> +    # Probe for support
>> +    xdp = cmd(f'{cfg.net_lib_dir / "xdp_helper"} - -', fail=False)
>> +    if xdp.ret == 255:
>> +        raise KsftSkipEx('AF_XDP unsupported')
>> +    elif xdp.ret > 0:
>> +        raise KsftFailEx('unable to create AF_XDP socket')
>> +
>> +    return bkg(f'{cfg.net_lib_dir / "xdp_helper"} {cfg.ifindex} {xdp_queue_id}',
>> +               ksft_wait=3)
>> +
>> +def check_xdp_bind(cfg):
>> +    ip(f"link set dev %s xdp obj %s sec xdp" %
>> +       (cfg.ifname, cfg.net_lib_dir / "xdp_dummy.bpf.o"))
>> +    ip(f"link set dev %s xdp off" % cfg.ifname)
>> +
>> +def check_rx_resize(cfg, queue_size = 128):
>> +    rx_ring = _get_rx_ring_entries(cfg)
>> +    ethtool(f"-G %s rx %d" % (cfg.ifname, queue_size))
>> +    ethtool(f"-G %s rx %d" % (cfg.ifname, rx_ring))
> Unfortunately this doesn't work on a basic QEMU setup:
>
> # ethtool -G eth0 rx 128
> [   15.680655][  T287] virtio_net virtio2 eth0: resize rx fail: rx queue index: 0 err: -2
> netlink error: No such file or directory
>
> Is there a way to enable more capable virtio_net with QEMU?

I guess that virtio-pci-legacy is used in your setup.

Here is how I setup virtio-net with Qemu

     -netdev tap,id=hostnet1,vhost=on,script=$NETWORK_SCRIPT,downscript=no \
     -device 
virtio-net-pci,netdev=hostnet1,iommu_platform=on,disable-legacy=on \

The iommu_platform=on is necessary to make vring use dma API which is a 
requirement to enable xsk_pool in virtio-net (XDP socket will be in 
zerocopy mode for this case). Otherwise, the XDP socket will fallback to 
copy mode, xsk_pool is not enabled in virtio-net that makes the 
probability to reproduce bug to be very small. Currently, when you don't 
have iommu_platform=on, you can pass the test even before the fix, so I 
think I will try to harden the selftest to make it return skip in this case.

Thanks,
Quang Minh.