On 08/11/17 12:18, Jan Beulich wrote: >>>> On 08.11.17 at 10:07, <jgross@xxxxxxxx> wrote: >> In case we are booted via the default boot entry by a generic loader >> like grub or OVMF it is necessary to distinguish between a HVM guest >> with a device model supporting legacy devices and a PVH guest without >> device model. >> >> PVH guests will always have x86_platform.legacy.no_vga set and >> x86_platform.legacy.rtc cleared, while both won't be true for HVM >> guests. >> >> Test for both conditions in the guest_late_init hook and set xen_pvh >> to true if they are met. > > This sounds pretty fragile to me: I can't see a reason why a proper > HVM guest couldn't come without VGA and RTC. That's not possible > today, agreed, but certainly an option down the road if virtualization > follows bare metal's road towards being legacy free. >From guest's perspective: what is the difference between a legacy free HVM domain and PVH? In the end the need for differentiating is to avoid access to legacy features in PVH as those would require a device model. Juergen
