Re: kern/59721: qemu VM's blackscreen over VNC wth -machine q35

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

I reproduced this with the following command line using qemu-10.1.1 on
a netbsd-10 kernel:

curl -L -O https://cdn.netbsd.org/pub/NetBSD/NetBSD-10.1/amd64/installation/cdrom/boot.iso
qemu-system-x86_64 -m 512m -cdrom boot.iso -machine q35 -accel nvmm

If I make any of the seven possible nonempty subsets of the following
changes, it works:

- replace `q35' by `pc'
- add `-bios $PREFIX/share/ovmf/OVMFX64.fd' (from sysutils/ovmf)
- remove `-accel nvmm'

The black screen failure is purely graphical.  If I do:

curl -L -O https://cdn.netbsd.org/pub/NetBSD/NetBSD-10.1/amd64/installation/cdrom/boot-com.iso
qemu-system-x86_64 -m 512m -cdrom boot-com.iso -machine q35 -accel nvmm -nographic

then it presents a serial console just fine.  And if I do:

qemu-system-x86_64 -m 512m -cdrom boot.iso -machine q35 -accel nvmm -serial mon:stdio -vga std

then I can blindly hit `3' to drop to the boot prompt and type
`consdev com0' and the bootloader prompt shows up at the serial
console, and the boot proceeds normally.

So something is screwy with BIOS boot graphics under -machine q35 with
NVMM.