[Bug 299491] bhyve: vatpit: accept mode 1 and emulate the channel 2 GATE (port 0x61)

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=299491

            Bug ID: 299491
           Summary: bhyve: vatpit: accept mode 1 and emulate the channel 2
                    GATE (port 0x61)
           Product: Base System
           Version: Unspecified
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: bhyve
          Assignee: virtualization@FreeBSD.org
          Reporter: david@crap.solutions

Created attachment 275815
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=275815&action=edit
bhyve: vatpit: accept mode 1 (hardware one-shot)

vatpit_update_mode() rejects the 8254 mode 1 (hardware retriggerable one-shot)
command and
returns an error; emulate_inout_port() maps a nonzero ioport handler result to
EIO, which is
returned from VM_RUN. A guest that programs mode 1 therefore aborts the VM with
"vm_run error -1, errno 5".

GNU Mach programs PIT channel 2 in mode 1 for its PIT-based delay
(sys/i386/i386/pit.c, pit_prepare_sleep()) during BSP bring-up, so GNU Mach
(Hurd) guests
cannot start under bhyve — observed on an AMD SVM host running 16-CURRENT.

Patch 1 accepts mode 1 as a hardware one-shot. Patch 2 additionally models the
channel 2 GATE
(port 0x61) and accepts mode 5, which GNU Mach's delay path also requires.

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