DTrace script to inspect VM exit reasons

[iximeow]

This script reports the SVM exit codes for vCPUs as well as some information for select exit codes that include additional information (port IO accesses and NPF/nested #PF).

The script also describes causes of Bogus exits out to the VMM. Other VM_EXITCODE_* causes are probably interesting too, but I'm not immediately sure what I'd want to know there.

The output looks something like this, from a mildly loaded propolis-standalone that happens to use the ACPI PM timer (seen as accesses to IO port 0xb008):

=== Exit summary, one second ending at 2025 Feb 14 23:47:33 ===
  SVM code  Count
        78        16
        64       514
        60       806
       400      1065
        7b      2611
IOIO SVM exits:
  Port   Op  OpSz  Addr  Count
  b008   in   32b   64b   2611
NPF SVM exits:
  Guest PA          Guest RIP         #PF flags  Count
          80011008  ffffffffc02521dd      D-UW-         0
          8001100c  ffffffffc02549dc      D-UW-         0
          fee00300  ffffffffa8065029      D-UR-         8
          fee00300  ffffffffa806504c      D-UW-         8
          fee00310  ffffffffa8065038      D-UW-         8
          fee000b0  ffffffffa806b472      D-UW-       516
          fee00380  ffffffffa806b472      D-UW-       525
vm_run() VM_EXITCODE_BOGUS reasons:
         early_bailout      108