Hi Zoran,
Thanks for your reply.
My situation is this: When the VM guest comes up the first time from a system-level reset (aka power on), the Broadwell HD graphics device runs fine. I see basic VGA both before and during the boot of Windows. Once Windows boots, the HD graphics device is configured by Intel's driver and I see hi-rez output. On a reboot of Windows within the VM, an FLR is issued. When the guest comes back up, no VGA. Windows does boot but provides no VGA output. If Windows needs to drop into VGA mode so that a user can access the real-mode functionality of the recovery console, still no VGA.
It's only on Broadwell-based boards that we have this problem. If we issue FLRs during the reset of the PCI bus for older Intel boards, no problem. We get VGA. Something involved with the FLR is messing up the state of the hardware instead of actually returning the hardware to a virgin state, akin to what you would get from a full system reset.
I was wondering if anyone had seen this kind of behavior. We've tried everything. We've manipulated all of the obvious HD graphics MMIO registers involved with restoring VGA but nothing seems to work.