frame buffer shared by domains on arch arm linux

[Mao Mingy <maomingya928@gmail.com>]

I am trying to run the PVHVM guest on omap5 (arm arch) so that I can get 
the frame buffer shared by Domains. my setup are:
1. run xen4.5 after the u-boot.
2. start the dom0 (on linux kernel 3.12) on xen.
3. run the qemu (from xen 4.5) and HVM backend on xen.
4. run the guest domain as "Machine: Dummy Virtual Machine, model: 
XENVM-4.5"
5. try to build a frame buffer on guest domain by
     CONFIG_XEN_FBDEV_FRONTEND = y
     CONFIG_FB_VIRTUAL=y

after change to domain checking in the first list of xenfb_init(...) in 
xen-fbfront.c from
     if (!xen_pv_domain()) --->    if (!xen_domain())
the /dev/fb0 is built up on guest domain. However, writing to this fb 
has no response from screen.

Why xenfb_init limited to PV domain only?

Is the PVHVM mode supported by xen4.5 and linux3.12?

Looks at the xen.h at the linux kernel source:
enum xen_domain_type {
     XEN_NATIVE,        /* running on bare hardware    */
     XEN_PV_DOMAIN,        /* running in a PV domain      */
     XEN_HVM_DOMAIN,        /* running in a Xen hvm domain */
};
seems PVHVM is not there yet?

Kindly enlighten me what could be the solution to get the frame buffer 
shared by Domains?

Regards,
Mao Mingya