Add initial minimal nested-svm-vmrun testcase

[bernhardkaindl]

Based on an initial experiment by Ross 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

[Copilot]

Pull request overview

Adds a new in-development XTF test intended to smoke-test Xen’s nested SVM support by entering an L2 guest via VMRUN using a minimal VMCB definition and a small assembly trampoline.

Changes:

• Introduces a new nested-svm-vmrun test target (Makefile + Xen config snippet).
• Adds a minimal VMCB layout header with compile-time offset/size checks.
• Implements the L1/L2 test logic in C plus an SVM VMLOAD/VMRUN/VMSAVE trampoline in assembly, and wires the test into the documentation index.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/nested-svm-vmrun/vmcb.h	Minimal VMCB struct layout + intercept/exitcode constants for the new test.
tests/nested-svm-vmrun/Makefile	Registers the new test build target and objects.
tests/nested-svm-vmrun/main.c	Implements L1 setup and L2 entry/handshake logic using a constructed VMCB.
tests/nested-svm-vmrun/extra.cfg.in	Enables nested HVM for the test domain.
tests/nested-svm-vmrun/entry.S	Provides the svm_vmrun() trampoline executing VMLOAD/VMRUN/VMSAVE.
docs/all-tests.dox	Adds the new test page to the global test list.

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[bernhardkaindl]

As I saw no further issues, I opened a PR for Andy's in repo:
andyhhp#13