[vfio-users] Heads up Arch users: potential breakage due to updates

[John Koelndorfer]

Hey folks,

Just writing to make other users aware that recent updates in Arch can
cause breakage in VFIO setups.

In a previous thread I wrote about how I was using an old version of OVMF
to maintain a respectable boot time for my Windows 10 VM. Well, after
updating recently that sort of bit me: an upgrade from Linux 4.12.4 and
qemu 2.9 to Linux 4.12.13 and qemu 2.10 resulted not only in my virtual
machine not booting, but my host system completely locking up a few seconds
after trying to boot the VM.

Per a thread on reddit [1] I tried a few different things:

1. Use the pc-q35-2.9 (I was using just "q35" before). This resulted in no
change of behavior. My host system still locked up.

2. Update to a new OVMF build from the Kraxel repo [2]
(edk2.git-ovmf-x64-0-20170907.b2970.gb575ca32c8.noarch.rpm). This fixed my
host system locking up, but my VM would get stuck on the Tianocore logo. I
left it run for multiple minutes with no successful boot. Qemu would
segfault if I interrupted it with ^C. I'd also see errors in dmesg about
one of my CPUs being locked up.

3. Switched my qemu machine type to "pc". Eureka! This worked. I am still
using the old version of OVMF, not the new one that I tried in step 2. For
reference, I have a copy in my GitHub repo [3].

Because the virtual hardware exposed to Windows 10 changed, it took quite a
bit longer than usual to boot for the first time after switching to the
"pc" machine type. It was stuck for maybe 5-10 minutes on an "Updating
devices" screen. Ultimately it did boot and things seem to be working. My
Windows 10 boot time is also back to normal.

Hope this saves someone a little bit of time.

John

[1]:
https://www.reddit.com/r/VFIO/comments/6z6i8/psa_if_you_use_the_q35_chipset_be_wary_of/
[2]: https://www.kraxel.org/repos/jenkins/edk2/
[3]:
https://github.com/jkoelndorfer/local-tools/blob/master/workstation/vfio/edk2.git-ovmf-x64-0-20150804.b1143.g8ca1489.noarch.rpm
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