Boxes gets into a 100% cpu loop while downloading Fedora images, doesn't redraw, is unresponsive
When I try to download a Fedora image through Boxes, Boxes UI gets almost unresponsive. The download progress bar doesn't redraw (it always seems to be at the beginning), any click on UI takes tens of seconds to perform the action, and GNOME regularly shows a dialog "Boxes is not responding: Force Quit / Wait". The longer you wait, the worse the UI responsiveness is. The gnome-boxes process takes 100% CPU, and the download seems to be happening in the background, but quite slow (about 5MB/s). The download speed definitely doesn't reflect the high CPU utilization.
The interesting part is - this happens only with Fedora images. I tested Fedora 36 Workstation, Fedora 36 Silverblue, Fedora 35 Workstation - happens to all of them. But if I try Ubuntu 22.04, openSUSE 15.4 or Debian 11, they work just fine! With openSUSE I get 3MB/s download speeds and 20% CPU utilization, with Ubuntu I get 50MB/s download speeds and 80% CPU utilization. The actual numbers don't matter, the important message is that with non-Fedora images, the CPU utilization reflects the download speed and is not 100%. With Fedora images, the CPU core is maxed out and the download is slow, so there's some CPU loop happening, which also makes the UI unresponsive.
There is nothing written in system journal during the download which could help debug the issue. Later, I'll try downloading from a different location, whether this is location specific (e.g. mirror selection when downloading). But even if it is, this shouldn't happen.
I've tested this on a cleanly installed Fedora 37 and also on a different PC with Fedora 37 upgraded from Fedora 36, happens on both of them.
gnome-boxes-43.0-1.fc37.1.x86_64
libvirt-libs-8.6.0-3.fc37.x86_64
qemu-kvm-7.0.0-9.fc37.x86_64
Fedora 37