display size 4096 or more is impossible; guest size is screen size modulo 4096

[schnidrig]

In Auto-resize Guest Display mode or also in Fullscreen mode on a very large screen (4096 pixels or more). I see the following wrong behaviour:

The guest's screen size is only actual screen size modulo 4096 rounded down to the next smaller multiple of 8. If the size is 4096, then 4096 % 4096 = 0, then the default 1024 width is applied. (or 768 for the height)

I tried setting different sizes with VBoxManage controlvm <VMName> setvideomodehint command.

I attached the VBox.log file. during that session I had executed the following commands:

VBoxManage controlvm Kubuntu setvideomodehint 4096 2160 32
VBoxManage controlvm Kubuntu setvideomodehint 4095 2160 32
VBoxManage controlvm Kubuntu setvideomodehint 4087 2160 32
VBoxManage controlvm Kubuntu setvideomodehint 8192 2160 32
VBoxManage controlvm Kubuntu setvideomodehint 8191 2160 32
VBoxManage controlvm Kubuntu setvideomodehint 8193 2160 32
VBoxManage controlvm Kubuntu setvideomodehint 9192 2160 32
VBoxManage controlvm Kubuntu setvideomodehint 1000 4095 32
VBoxManage controlvm Kubuntu setvideomodehint 1000 4096 32
VBoxManage controlvm Kubuntu setvideomodehint 0 0 32
VBoxManage controlvm Kubuntu setvideomodehint 4088 2160 32

In the log file one can see, that the resulting guest display size is wrong whenever w > 4095 or h > 4095

00:00:15.395987 VMMDev: SetVideoModeHint: Got a video mode hint (4096x2160x32)@(0x0),(1;0) at 0
00:00:15.439417 Display::handleDisplayResize: uScreenId=0 pvVRAM=00000001266af000 w=1024 h=2160 bpp=32 cbLine=0x1000 flags=0x1

00:02:15.240295 VMMDev: SetVideoModeHint: Got a video mode hint (4095x2160x32)@(0x0),(1;0) at 0
00:02:17.409141 Display::handleDisplayResize: uScreenId=0 pvVRAM=00000001266af000 w=4088 h=2160 bpp=32 cbLine=0x3FE0 flags=0x1

00:02:56.419179 VMMDev: SetVideoModeHint: Got a video mode hint (4087x2160x32)@(0x0),(1;0) at 0
00:02:58.579637 VBVA: InfoScreen: [0] @0,0 4080x2160, line 0x3fc0, BPP 32, flags 0x1

00:03:19.311747 VMMDev: SetVideoModeHint: Got a video mode hint (8192x2160x32)@(0x0),(1;0) at 0
00:03:20.454025 Display::handleDisplayResize: uScreenId=0 pvVRAM=00000001266af000 w=1024 h=2160 bpp=32 cbLine=0x1000 flags=0x1

00:03:25.949484 VMMDev: SetVideoModeHint: Got a video mode hint (8191x2160x32)@(0x0),(1;0) at 0
00:03:28.074011 Display::handleDisplayResize: uScreenId=0 pvVRAM=00000001266af000 w=4088 h=2160 bpp=32 cbLine=0x3FE0 flags=0x1

00:03:43.210929 VMMDev: SetVideoModeHint: Got a video mode hint (8193x2160x32)@(0x0),(1;0) at 0
00:03:44.349569 Display::handleDisplayResize: uScreenId=0 pvVRAM=00000001266af000 w=2560 h=1600 bpp=32 cbLine=0x2800 flags=0x1

00:04:06.325388 VMMDev: SetVideoModeHint: Got a video mode hint (9192x2160x32)@(0x0),(1;0) at 0
00:04:08.445923 VBVA: InfoScreen: [0] @0,0 1000x2160, line 0xfa0, BPP 32, flags 0x1

00:04:43.460792 VMMDev: SetVideoModeHint: Got a video mode hint (1000x4095x32)@(0x0),(1;0) at 0
00:04:45.586547 Display::handleDisplayResize: uScreenId=0 pvVRAM=00000001266af000 w=1000 h=4095 bpp=32 cbLine=0xFA0 flags=0x1

00:04:49.388757 VMMDev: SetVideoModeHint: Got a video mode hint (1000x4096x32)@(0x0),(1;0) at 0
00:04:51.501883 Display::handleDisplayResize: uScreenId=0 pvVRAM=00000001266af000 w=1000 h=768 bpp=32 cbLine=0xFA0 flags=0x1

00:05:34.159715 VMMDev: SetVideoModeHint: Got a video mode hint (4088x2160x32)@(0x0),(1;0) at 0
00:05:35.290404 VBVA: InfoScreen: [0] @0,0 4088x2160, line 0x3fe0, BPP 32, flags 0x1

it looks like the size is only an 8 bit integer. The lowest 4 bits are always 0 and bits 13 and up are lost.

I tried this with several Linux distributions (Ubuntu, Kubuntu, Mint, Fedora). The behaviour is always the same.

[schnidrig]

VBox.log

[schnidrig]

The Problem still exists in 5.1.4

[Michael Thayer]

Could you please give more precise details about affected guests? A precise version of Ubuntu which is affected after a fresh installation for example.