Re: [edk2-devel] GuestPhysAddrSize questions

["Gerd Hoffmann" <kraxel@redhat.com>]

  Hi,

> >    23:16 GuestPhysAddrSize Maximum guest physical address size in bits.
> >                            This number applies only to guests using nested
> >                            paging. When this field is zero, refer to the
> >                            PhysAddrSize field for the maximum guest
> >                            physical address size. See “Secure Virtual
> >                            Machine” in APM Volume 2.

> I believe the main purpose of GuestPhysAddrSize was for software use (for
> nested virtualization) and that the hardware itself has always returned zero
> for that value. So you should be able to use that field. Adding @Paolo for
> his thoughts.

Posted patches for kernel
https://lore.kernel.org/kvm/20240301101410.356007-1-kraxel@redhat.com/
and qemu
https://lore.kernel.org/kvm/20240301101713.356759-1-kraxel@redhat.com/
(sorry forgot to Cc you).

Reviewers mentioned this is meant for nested guests, i.e. (if I
understand this correctly) the l0 hypervisor can use that to tell
the l1 hypervisor what the l2 guest phys-bits should be.

Is this nested virtualization use documented somewhere?  Tried to
search for GuestPhysAddrSize or Fn8000_0008_EAX in APM Volume 2,
found nothing.

Is there any case where the phys-bits limits for an l1 guest and
l2 guest would be different?

thanks & take care,
  Gerd



-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#116313): https://edk2.groups.io/g/devel/message/116313
Mute This Topic: https://groups.io/mt/104510523/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-