* Re: [LTP] [RFC] loading vmw_vsock_virtio_transport by systemd breaks vsock_loopback autoloading
[not found] ` <acqLo6-IQVBzY3UW@sgarzare-redhat>
@ 2026-03-30 23:09 ` Petr Vorel
0 siblings, 0 replies; only message in thread
From: Petr Vorel @ 2026-03-30 23:09 UTC (permalink / raw)
To: Stefano Garzarella
Cc: Andrei Borzenkov, netdev, virtualization, Luca Boccassi,
Valentin Lefebvre, ltp, Yu Watanabe, Luca Boccassi
[ Cc LTP ML ]
> On Fri, Mar 20, 2026 at 12:02:24PM +0100, Petr Vorel wrote:
> > Hi all,
> > there is a systemd bug [1] which causes vsock_loopback not to be autoloaded due
> > previous loading vmw_vsock_virtio_transport in an early phase of boot.
> > vmw_vsock_virtio_transport requires vmw_vsock_virtio_transport_common and vsock,
> > vsock_loopback requires vsock.
> > Reproducer: [2].
> > Proposed fix in systemd: [3]
> > While I think the bug should be fixed in systemd with proposed fix [3] we'd like
> > to know opinion of the kernel vsock developers in case there is a way to improve
> > vsock modules autoloading.
> The original idea of vsock_loopback was to be used just for
> testing/debugging, so maybe even the autoloading when no other transport was
> loaded wasn't a great idea, but at the time we thought it might be useful
> for testing.
Stefano, thanks for info.
> In general, therefore, if you want to use the loopback, it's always best to
> load vsock_loopback.
> What use case is being affected by the fact that vsock_loopback isn't loaded
> automatically?
It's actually testing. Only LTP test cve-2025-21756.c [1] used it.
Reported [2], fixed in systemd [3].
Of course we could call 'modprobe vsock_loopback' in the test, but now not
needed as as fixed in systemd.
I wonder who else uses the module. Searching in Debian's codesearch I see mostly
testing code (+ now systemd :)).
Kind regards,
Petr
[1] https://github.com/linux-test-project/ltp/blob/master/testcases/cve/cve-2025-21756.c
[2] https://github.com/systemd/systemd/issues/41100
[3] https://github.com/systemd/systemd/commit/7c1075fb8ff2d3b87fa463d542e2e00ac086cbd3
[4] https://codesearch.debian.net/search?q=vsock_loopback&perpkg=1&page=1
> Thanks,
> Stefano
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