I recently changed my KVM servers to use the kernel command-line parameter nomodeset for the virtual machine kernels so that they don’t try to go into graphics mode. I do this because I don’t have X11 or VNC enabled and I want a text console to use with the -curses option of KVM. Without the nomodeset KVM just says that it’s in 1024*768 graphics mode and doesn’t display the text.
Now my KVM server running Debian/Unstable has had it’s virtual machines start going into graphics mode in spite of nomodeset parameter. It seems that an update to QEMU has added a new virtual display driver which recent kernels from Debian/Unstable support with the bochs_drm driver, and that driver apparently doesn’t respect nomodeset.
The solution is to create a file named /etc/modprobe.d/blacklist.conf with the contents “blacklist bochs_drm” and now my virtual machines have a usable plain-text console again! This blacklist method works for all video drivers, you can blacklist similar modules for the other virtual display hardware. But it would be nice if the one kernel option would cover them all.