Nested Virtualization: Overview

Hi!

This patch series brings Nested Virtualization to Xen. This is the third patch series. Improvements to the previous patch submission:

- implement HVM-on-HVM (instead of SVM-on-HVM)
- move cpuid handling into tools (per Keir's request)

There might still be some nuances to fiddle with to make it fit for VMX. Feedback from Intel is appreciated, therefore.

The patch series:

patch 01: add nestedhvm guest config option to the tools.
This is the only one patch touching the tools
patch 02: change local_event_delivery_* to take vcpu argument.
This prevents spurios xen crashes on guest shutdown/destroy with nestedhvm enabled.
patch 03: Add data structures for nested virtualization.
patch 04: add nestedhvm function hooks, described in XenNestedHVM.pdf patch 05: The heart of nested virtualization.
patch 06: Allow switch to paged real mode during vmrun emulation.
Emulate cr0 and cr4 when guest does not intercept them (i.e. Hyper-V/Windows7, KVM)
patch 07: When injecting an exception into nested guest, inject
#VMEXIT into the guest if intercepted
patch 08: Allow guest to enable SVM in EFER
patch 09: Handle interrupts (generic part)
patch 10: SVM specific implementation for nested virtualization patch 11: Handle interrupts (SVM specific)
patch 12: The piece of code that effectively turns nested virtualization on.
Use HVM_PARAM_* this time.
patch 13: Change p2m infrastructure to operate with per-p2m instead
of per-domain. Combined with patch 15, this allows to run nested guest with hap-on-hap.
patch 14: Handle nested pagefault to enable hap-on-hap and handle
nested guest page-table-walks to emulate instructions the guest does not intercept (i.e. WBINVD with Windows 7).

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