[Qemu-devel] OVMF, SeaBIOS & non-CSM based legacy boot

[Jordan Justen]

This weekend I spent some time working on loading SeaBIOS from OVMF to
start a legacy boot.  I was able to get x86 & x86-64 Linux to legacy
boot using this method.

Unfortunately, (I think) it is not nearly as nice a having a true CSM.
 Basically, you have to decide at some point in the OVMF boot that you
want to legacy boot, and once you start SeaBIOS running, OVMF/UEFI
will never be in the picture again (until system reset).

Contrast this to using a CSM where you can:
* Load a legacy option ROM (vbios, or disk rom),
  and use it during a UEFI boot
* Fail a legacy boot, and potentially return back to UEFI if it fails.
  (Not in all cases, if the failed boot alters the system state significantly)
* Specify via UEFI the boot process which disk to legacy boot in the CSM

So, would this be valuable (in the short term) to help move forward
QEMU's usage of OVMF and add UEFI support?  Or would QEMU require true
CSM support?

Thanks,

-Jordan