Bug report for 'vga none' qemu option not working any more

[Sergey Aleynikov]

I'm running a lot of qemu + kvm + seabios VMs and after upgrade to
Debian 9 I found that some of them stopped booting. After trying to
change kernel/qemu/seabios versions, I've nailed down the cause to the
following:

# VM definition
qemu-system-x86_64 \
        -enable-kvm \
        -machine q35 \
        -m 512 \
        -nodefaults \
        -cpu host \
        -smp 1,sockets=1,cores=1,threads=1 \
        -bios /opt/seabios/out/bios.bin \
        -device virtio-scsi-pci,id=scsi \
        -drive file="disk.img",id=disk,format=raw,if=none,cache=unsafe,aio=threads
\
        -device scsi-hd,drive=disk,bus=scsi.0,removable=off \
        -device
virtio-net-pci,netdev=net0,mac=$("../qemu-mac-hasher.py" "test") \
        -netdev tap,id=net0,script="../ifup.sh",downscript="../ifdown.sh" \
        -chardev stdio,id=seabios -device
isa-debugcon,iobase=0x402,chardev=seabios \
        -vga none \
        -nographic

This VM doesn't boot with modern seabios, but it used to work. And
now, if I change 'vga none' to 'vga std' in it, it starts booting
again. I've performed git bisect on the seabios repository and found
the following commit to break the old setup:

1d9e87b937d646be1950695f9ead35100d5ebbe6 is the first bad commit
commit 1d9e87b937d646be1950695f9ead35100d5ebbe6
Author: Gerd Hoffmann 
Date:   Fri Jun 26 09:44:00 2015 +0200

virtio: run drivers in 32bit mode

virtio version 1.0 registers can (and actually do in the qemu
    implementation) live in mmio space.  So we must run the blk and
    scsi virtio drivers in 32bit mode, otherwise we can't access them.

This also allows to drop a bunch of GET_LOWFLAT calls from the virtio
    code in the following patches.

Signed-off-by: Gerd Hoffmann

:100644 100644 f97b1bd9f91df7417e7bd5a1ebd7182098a43296
e287530d0008e1d876a0bb9f9ff8a43266d7e1bd M Makefile
:040000 040000 70b419ced4f58a39143c92897097a08b5548cbf4
93f7d4d939b5e0a14102a3cb718b1be5a2f12e60 M src

Here're links to a full successful boot log (with 'vga std') and some
portion of a failing boot log (as it just loops eternally):

https://gist.github.com/dur-randir/80b7d9a84cbdb8591ec05abe2fc62604
https://gist.github.com/dur-randir/52c31d2abe3150759abd3e8ca140959a

Those logs were obtained from seabios 1d9e87b937 - the first broken
revision, but I can provide them for master, as it's still broken.

Best regards,
Sergey Aleyinkov