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

[Jason Wang]

On Wed, Apr 16, 2025 at 2:54 PM Bui Quang Minh <minhquangbui99@xxxxxxxxx> wrote:
>
> 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?

What's the qemu command line and version?

Resize depends on queue_reset which should be supported from Qemu 7.2

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

Note that modern devices are used by default.

>
> 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.

I would like to keep the resize test as it doesn't require iommu_platform.

Thanks

>
> Thanks,
> Quang Minh.
>