xen discuss - Dec 2005 - [xen-discuss] x86 and sparc virtualizability and Xen nestability

My understanding is that Intel and AMD, with their Vanderpool and Pacifica x86
extensions, are fixing the design flaw in the x86 architecture (some sensitive
instructions which couldn''t be trapped) which prevented x86 from being
fully virtualizable, i.e. which prevented the architecture from satisfying the
Popek and Goldberg virtualization requirements. (And while they''re at
it they''re also modifying the design to make virtualization not only
possible but also fast.)
See http://en.wikipedia.org/wiki/Popek_and_Goldberg_virtualization_requirements
for details.
Can anybody confirm that with the extensions, x86 does in fact satisfy the
requirements?

Which leads to another question (even though Xen doesn''t run on sparc):
does sparc satisfy the requirements?

And a third question: if x86 with the extensions does satisfy the requirements,
then it also automatically supports virtual machine nesting, assuming that the
hypervisor is designed to support that feature. So, will Xen support nesting on
such processors?
This message posted from opensolaris.org

Both Vanderpool and Pacifica do allow you to trap (or have the machine handle)
all the instructions that were problematic before (and also include
virtualisation-related performance enhancements).  The question is, whether the
new VT/SVM instructions can also be trapped...  This is certainly true in
Pacifica, the Vanderpool documentation doesn''t state it explicitly but
I''d be surprised if Intel were insane enough for it not to be the case
there also!

Virtual machines provided by Xen 3.0 are *not* Vanderpool / Pacifica capable. 
You could run non-Vanderpool (or Pacifica) Xen under Xen on Vanderpool /
Pacifica hardware - that should work now, if you have the relevant kit.  What
isn''t yet possible is running a Vanderpool (or Pacifica) Xen, inside
another Vanderpool (or Pacifica) Xen, for arbitrary nesting, since Xen
doesn''t emulate the additional instructions required.

It''s technically possible to provide Vanderpool / Pacifica capabilities
to guest virtual machines, so this may be added at a later date.

(side note: questions that aren''t Sun-specific are also worth asking on
the Xen mailing lists)
This message posted from opensolaris.org