[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 #51 from Tommy P <tommyhp2 at gmail.com> ---
(In reply to John Hartley from comment #47)

Hi John,

Before making the patch for disabling VirtIO + netmap interop, I thought of
possible scenarios:

1) netmap w/o VirtIO
2) netmap + VirtIO interop
3) VirtIO w/o netmap

For 1 & 3, disabling in the kernel, IMO, is the best approach over all.  Thus,
no need for any change in the code.  As for 2, netmap currently doesn't fully
supports PCI-e.  Thus, the approach I took is what I think is best (kernel
compile time, kernel size, least time spent of making a patch that works which
was less than 5 minutes, easier future code adaptation to Vincenzo's changes of
netmap).  This would allow both netmap and VirtIO to work in conjunction except
netmap + VirtIO NIC.

As for QEMU 4.0+ versus older versions (comment #50), I think it may come down
to compatibility matrix between FreeBSD vs QEMU versions.  I previously had
problems booting older versions of FreeBSD when I specify CPU model Opterion_G4
or Opteron_G5 within QEMU/KVM configuration.  Now, I can run both 11 & 12 with
Opteron_G5.  If you think as a developer/programmer and consider the SDLC,
would you want to make something that's constantly changing or something that's
stable?  For those reasons, I stopped using non LTS for Ubuntu a couple of
years ago because the downstream needs time in accordance with SDLC to update
for the changes.

Regards,
Tommy

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