[Qemu-discuss] Modifier keys (CTRL, SHIFT) not working correctly in guest

[Miguel Dilaj]

Hello everyone,

First post, so please let me know if I'm missing something.

Host: Kubuntu 18.04.1 LTS
Kernel: 4.15.0-30-generic SMP x86_64
KDE: 5.47.0
qemu: 2.11+dfsg-iu
libvirt: 4.0.0-1ubuntu8

Guest: Windows 10
Latest GA packages installed

I use remote-viewer to connect using SPICE. The guest is dual-head (two 
virtual monitors, via two QXL adapters).

The above was working OK until I upgraded from Kubuntu 16.04 to 18.04 
last week, which caused most if not all packages to be upgraded (of 
course kernel, KDE components, qemu and libvirt were upgraded).

Since then, I've a strange behavior with SHIFT and CTRL (probably ALT as 
well, but that one is not used much) modifier keys.
Let me exemplify it with CTRL-C and CTRL-V (clipboard copy and paste) 
which are used a lot.
When I press CTRL-C or CTRL-V, sometimes these work OK. Sometimes I just 
get a 'c' or 'v', as if the modifier key was never pressed.
Sometimes I can "force" it to work OK by ensuring CTRL is pressed for 1 
second prior to pressing C or V, which is extremely annoying.
Also, and this is related exclusively to pasting, sometimes when I try 
to paste what was copied the application receiving the past freezes for 
a couple seconds, and nothing is pasted. The solution is copying the 
content again, and trying to paste again.

Needless to say, the physical keyboard works OK, and the modifier keys 
also work OK on the host. The problem can only be observed on the guest.

The SPICE channel and QXL video devices on the guest seem to be OK.

Cannot find any relevant info in the system logs.

I Googled, checked the keyboard configuration, disabled desktop 
extensions, reinstalled the GA on the guest, etc, but the problem persists.

Does anyone ever had the above issue and have a clue on where to carry 
on with the investigation?
Alternatively, and hints on how to debug keyboard handling in guest, 
host, and the host-guest interaction?

Thank you in advance!
Kind regards,

Miguel