[Qemu-devel] virtio-gpu: bug report : vnc connect can not display when migrate to destination.

[wanghaibin]

Hi, all:

I met a problem.

I boot a aarch64 kernel with virtio-gpu device on aarch64 board. The cmdline 
just like：

qemu-system-aarch64 -name guest=vm,debug-threads=on -S -machine 
virt-2.6,accel=kvm,usb=off,gic-version=3 -cpu host -m 8192 -realtime mlock=off 
-smp 4,sockets=4,cores=1,threads=1
-no-user-config -nodefaults -no-shutdown -boot strict=on -kernel 
/mnt/linux-stable/arch/arm64/boot/Image -append console=ttyAMA0 root=/dev/sda2 
earlyprintk=pl011,0x9000000 rw
-device ioh3420,port=0x8,chassis=1,id=pci.1,bus=pcie.0,addr=0x1 -device 
i82801b11-bridge,id=pci.2,bus=pcie.0,addr=0x2 -device 
pci-bridge,chassis_nr=3,id=pci.3,bus=pci.2,addr=0x0
-device ioh3420,port=0x18,chassis=4,id=pci.4,bus=pcie.0,addr=0x3 -device 
ioh3420,port=0x20,chassis=5,id=pci.5,bus=pcie.0,addr=0x4 -device 
ioh3420,port=0x28,chassis=6,id=pci.6,bus=pcie.0,addr=0x5
-device usb-ehci,id=usb,bus=pci.3,addr=0x1 -device 
virtio-scsi-pci,id=scsi0,bus=pci.4,addr=0x0 -drive 
file=/mnt/euler_b500.raw,format=raw,if=none,id=drive-scsi0-0-0-0,cache=none,aio=native
-device 
scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1
 -netdev tap,fd=27,id=hostnet0,vhost=on,vhostfd=28
-device 
virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:af:3c:c5,bus=pci.1,addr=0x0 
-serial pty -device usb-tablet,id=input0 -device usb-kbd,id=input1
-vnc 0.0.0.0:0 -device virtio-gpu-pci,id=video0,bus=pci.5,addr=0x0

Using the VNC4 client connect to the vm, every is OK.

After migrate to destination, Using the VNC4 client connect to the vm , it 
cannot display normally. Using the tightVNC client, display normally.


I try to debug this problem, and the info just as follow:
(1) Guest kernel driver use soft_cursor update the cursor, not the virtio-gpu 
driver virtio_gpu_cursor_ping func
    (qemu virtio-gpu backend does not call update_cursor)
(2) Migrate to destination, I notice virtio_gpu_load func will call 
update_cursor (call to vnc_dpy_cursor_define, define vd->cursor).
    At the source, vd->cursor is not define.
(3) After migrate, using the VNC4 client, display failed caused by 
set_encodings(VNC_ENCODING_RICH_CURSOR: vnc_cursor_define(vs);, i don't know 
why),


I don't understand very well about console, virtio-gpu, I just doubt this 
problem though compared the source and destination state difference.
So just supply these message.

BTW: just a simple test, delete the virtio_gpu_load func update_cursor line, 
VNC4 client display OK at destination ...


Thanks.