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

["Michael van Elst via gnats" <gnats-admin%NetBSD.org@localhost>]

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

From: mlelstv%serpens.de@localhost (Michael van Elst)
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/59721: qemu VM's blackscreen over VNC wth -machine q35
Date: Fri, 24 Oct 2025 08:55:45 -0000 (UTC)

 roy%marples.name@localhost writes:
 
 >Starting a QEMU VM with -machine q35 and -accel nvmm results in a black screen over VNC. Network probes (aka no DHCP request) show the VM isn't functioning.
 
 The VM is starting with serial console and shows:
 
 [     1.019149] pci0 at mainbus0 bus 0: configuration mode 1
 [     1.019149] pci0: i/o space, memory space enabled, rd/line, rd/mult, wr/inv ok
 [     1.019149] pchb0 at pci0 dev 0 function 0: Intel 82G33/P35 Host Bridge (rev. 0x00)
 [     1.019149] agp0 at pchb0autoconfiguration error: : can't find internal VGA config space
 [     1.019149] vga0 at pci0 dev 1 function 0: vendor 1234 product 1111 (rev. 0x02)
 [     1.019149] wsdisplay0 at vga0 kbdmux 1
 [     1.019149] wsmux1: connecting to wsdisplay0
 [     1.019149] wskbd0: connecting to wsdisplay0
 [     1.019149] drm at vga0 not configured
 
 with no tty attached to wsdisplay0.
 
 With a VNC console, NVMM spits out lots of Unexpeced MSR accesses
 and the machine doesn't come up. The same happens for a regular
 graphical console.
 
 In the latter case qemu also segfaults when shutting down in an atexit()
 routine,
 
 No such problems when NVMM is not in use.
 
 Here is how I start qemu:
 
 qemu-system-x86_64 \
         -accel nvmm \
         -machine q35 \
         -cpu host \
         -display vnc=0.0.0.0:0 \
         -serial mon:stdio \
         -m 256 \
         -smp 1 \
         -rtc base=utc,clock=host \
         \
         -netdev tap,id=n1,ifname=tap0,script=no,downscript=no \
         -device virtio-net,netdev=n1 \
         \
         -device virtio-blk,drive=d0,bootindex=2 \
         -drive if=none,format=qcow2,file=disk.qcow2,id=d0 \
         \
         -device virtio-scsi,id=scsi0 \
         -device scsi-cd,bus=scsi0.0,drive=d1 \
         -drive if=none,id=d1,media=cdrom,read-only=on,index=1,format=raw,file=bo
 ot-com.iso