On Wed, Jun 13, 2018 at 01:50:47PM -0600, Alex Williamson wrote:
On Wed, 13 Jun 2018 10:41:49 +0200 Gerd Hoffmann <kraxel@redhat.com> wrote:
So we have a boot display when using a vgpu as primary display.
Use vfio-pci-ramfb instead of vfio-pci to enable it.
Using a different device here seems like it almost guarantees a very complicated path to support under libvirt. What necessitates this versus a simple ramfb=on option to vfio-pci?
Well, it's simliar to qxl vs. qxl-vga. It's not qxl,vga={on,off} and libvirt has no problems to deal with that ... Another more technical reason is (again) hotplug. ramfb needs an fw_cfg entry for configuration, and fw_cfg entries can't be hotplugged. So hotplugging vfio-pci with ramfb=on isn't going to fly. So we need a separate device with hotplug turned off.
I'm also not sure I understand the usage model, SeaBIOS and OVMF know how to write to this display, but it seems that the guest does not.
Yes.
I suppose in the UEFI case runtime services can be used to continue writing this display,
Yes.
but BIOS doesn't have such an option, unless we're somehow emulating VGA here.
vgabios support is in the pipeline, including text mode emulation (at vgabios level, direct access to vga window @ 0xa0000 doesn't work).
So for UEFI, I can imagine this covers us from power on through firmware boot and up to guest drivers initializing the GPU (assuming the vGPU supports a kernel mode driver, does NVIDIA?),
Yes. Shouldn't matter whenever the driver is kernel or userspace.
but for BIOS it seems we likely still have a break from the bootloader to GPU driver initialization.
Depends. vgacon (text mode console) doesn't work. fbcon @ vesafb works.
For instance, what driver is used to draw the boot animation (or blue screen) on SeaBIOS Windows VM?
Windows depends on vgabios for that and it works fine.
I'm assuming that this display and the vGPU display are one in the same, so there's some cut from one to the other.
Yes. If the vfio query plane ioctl reports a valid guest video mode configuration the vgpu display will be used, ramfb otherwise. cheers, Gerd