vmm: Suspend the VM on a hardware triple fault

[hayzam_gmail.com]

Summary

The VMX backend did not handle EXIT_REASON_TRIPLE_FAULT, so a hardware
triple fault fell through as an unhandled exit: bhyve printed a raw VMX
exit dump and aborted, instead of suspending the VM with the
reason the software exception path already uses.

Add the missing case so the VM suspends with VM_SUSPEND_TRIPLEFAULT and
bhyve exits with BHYVE_EXIT_TRIPLEFAULT. This matches illumos change 14664.

Obtained from: illumos 83b49c54d9c0766e810b6c8ff849dfb6693fc68a

[bnovkov]

LGTM, I'll give the patch a spin tomorrow before landing it. Have you tested this change somehow already?

[hayzam_gmail.com]

In D59840#1373292, @bnovkov wrote:

LGTM, I'll give the patch a spin tomorrow before landing it. Have you tested this change somehow already?

Yep, I tested with a small 16-bit payload that loads a null IDT and executes ud2, so the guest takes a hardware triple fault (VMX exit reason 2).

Before: raw VMX dump, then abort.
After patch: no dump, exits 3 (BHYVE_EXIT_TRIPLEFAULT).

Only the VMX side is covered though as you can see, the SVM side still injects #UD for VMCB_EXIT_SHUTDOWN (illumos I believe handles it in 13170), and I have no AMD hardware here.

I can attach the payload image and both serial logs if that's useful.