If the HVM pauses on boot and shows a series of warnings, visit HVM Troubleshooting for a fix.
Some kernel/Xorg combinations use only 640x480 in HVM, which is quite small. To enable maximum resolution, some changes in the Xorg configuration are needed:
To achieve it (all commands to be run as root):
Generate XOrg configuration (if you don't have it):
X -configure :1 && mv ~/xorg.conf.new /etc/X11/xorg.conf
Add HorizSync line to Monitor section, it should look something like:
Section "Monitor"
Identifier "Monitor0"
VendorName "Monitor Vendor"
ModelName "Monitor Model"
HorizSync 30.0 - 60.0
EndSection
Change driver to "vesa" in Device section:
Section "Device"
# (...)
Identifier "Card0"
Driver "vesa"
VendorName "Technical Corp."
BoardName "Unknown Board"
BusID "PCI:0:2:0"
EndSection
Now you should get resolution of at least 1280x1024 and should be able to choose other modes.
Linux Qubes agents are written primarily for PV qubes, but it is possible to run them also in a HVM qube. However some work may be required to achieve this. Check this thread.