[CentOS] KVM Linux Guest Resolution only 1024x768

Sun May 4 07:39:05 UTC 2014
Chris <ch2009 at arcor.de>

Dear All,

I'm trying to install a Debian Wheezy KVM guest on a CentOS 6.4 Host.
The only resolutions supported are 1024x768 or 800x600.

I increased the video RAM to 500 MB, but the guest still says:

[    10.321] (II) CIRRUS(0): Not using default mode "1920x1200"
(insufficient memory for mode)

Only 32 MB are recognized:

00:02.0 VGA compatible controller: Cirrus Logic GD 5446 (prog-if 00 [VGA
controller])
        Subsystem: Red Hat, Inc Device 1100
        Physical Slot: 2
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop-
ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort-
<TAbort- <MAbort- >SERR- <PERR- INTx-
        Region 0: Memory at f0000000 (32-bit, prefetchable) [size=32M]
        Region 1: Memory at f2000000 (32-bit, non-prefetchable) [size=4K]
        Expansion ROM at f2010000 [disabled] [size=64K]

How can I increase the resolution? Are any guest modifications necessary?

-- 
Christian