[Bug 236922] Virtio fails as QEMU-KVM guest with Q35 chipset on Ubuntu 18.04.2 LTS

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236922

--- Comment #38 from Tommy P <tommyhp2 at gmail.com> ---
Created attachment 210723
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=210723&action=edit
Recent update in stable/12 for VirtIO

r347233:

Remove non-functional SCTP checksum offload support for virtio.

Checksum offloading for SCTP is not currently specified for virtio.
If the hypervisor announces checksum offloading support, it means TCP
and UDP checksum offload. If an SCTP packet is sent and the host announced
checksum offload support, the hypervisor inserts the IP checksum (16-bit)
at the correct offset, but this is not the right checksum, which is a CRC32c.
This results in all outgoing packets having the wrong checksum and therefore
breaking SCTP based communications.

This patch removes SCTP checksum offloading support from the virtio
network interface.

Thanks to Felix Weinrank for making me aware of the issue.

Reviewed by:            bryanv@
MFC after:              1 week
https://svnweb.freebsd.org/base?view=revision&revision=347233
-------------------------------------------------------------
r349285:

VirtIO SCSI:  validate seg_max on attach

Until r349278, bhyve presented a seg_max to the guest that was too large.
Detect this case and clamp it to the virtqueue size.  Otherwise, we would
fail the "too many segments to enqueue" assertion in virtqueue_enqueue().

I hit this by running a guest with a MAXPHYS of 256 KB.

Reviewed by:    bryanv cem
MFC after:      1 week
Sponsored by:   Dell EMC Isilon
https://svnweb.freebsd.org/base?view=revision&revision=349285

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