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

["Taylor R Campbell via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/59721; it has been noted by GNATS.

From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
To: Roy Marples <roy%marples.name@localhost>,
	Michael van Elst <mlelstv%serpens.de@localhost>,
	Martin Husemann <martin%duskware.de@localhost>
Cc: gnats-bugs%NetBSD.org@localhost, netbsd-bugs%NetBSD.org@localhost
Subject: Re: kern/59721: qemu VM's blackscreen over VNC wth -machine q35
Date: Sun, 26 Oct 2025 16:03:05 +0000

 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 -no=
 graphic
 
 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.