Add initial minimal nested-svm-vmrun testcase

[bernhardkaindl]

Based on an initial experiment by Ross.

I refactored it with these changes (summary):

• vmcb.h: replaced the GPL-only 640-line copy of Xen's vmcb_struct (with all its bit-fields, unions and VMCB_ACCESSORS macros) with a 128-line BSD-licensed minimal struct vmcb. Only the fields the test actually uses are named; reserved areas are kept as anonymous padding. _Static_asserts pin all named fields to their architectural offsets per the AMD APM Vol. 2 Appendix B layout.
• main.c: dropped the horrible vmcb_set_* accessors in favour of plain field assignments (l2_vmcb.cr3 = read_cr3();). Replaced the lidt + ud2 shutdown trick (which depended on SHUTDOWN intercept) with a clean L2 → L1 handshake: L2 writes a sentinel, executes HLT (intercepted), L1 verifies both the exit code and the sentinel. Removed dead code (l2_cpuinfo, the GDT/TSS plumbing the test never used, the result/shutdown_ptr globals, the #if 0 block).
• entry.S: collapsed the 100-line l2_cpuinfo save/restore (which was never populated from C) to a 6-instruction trampoline. Documented why VMSAVE/VMLOAD of the L2 VMCB bracket the VMRUN.
• setup.c: restored the original xen_console_write body — the L2-side console garbling went away once L2 stopped trying to invoke the inherited Xen hypercall page (in Xen's nested-SVM model, VMMCALL from L2 unconditionally exits to L1, so L2 cannot hit Xen's hypercall path; the new test sticks to a pure HLT exit)

Signed-off-by: Ross Lagerwall ross.lagerwall@citrix.com
Signed-off-by: Bernhard Kaindl bernhard.kaindl@citrix.com