x86emul: New return code for unimplemented instruction

x86emul: New return code for unimplemented instruction

Enforce the distinction between an instruction not implemented by the
emulator and the failure to emulate that instruction by defining a new
return code, X86EMUL_UNIMPLEMENTED.

This value should only be returned by the core emulator when a valid
opcode is found but the execution logic for that instruction is missing.
It should NOT be returned by any of the x86_emulate_ops callbacks.

e.g. hvm_process_io_intercept should not return X86EMUL_UNIMPLEMENTED.
The return value of this function depends on either the return code of
one of the hvm_io_ops handlers (read/write) or the value returned by
hvm_copy_guest_from_phys / hvm_copy_to_guest_phys.

Similary, none of this functions should return X86EMUL_UNIMPLEMENTED.
 - hvm_io_intercept
 - hvmemul_do_io
 - hvm_send_buffered_ioreq
 - hvm_send_ioreq
 - hvm_broadcast_ioreq
 - hvmemul_do_io_buffer
 - hvmemul_validate

Also the behavior of hvm_emulate_one_insn and vmx_realmode_emulate_one
was modified to generate an Invalid Opcode trap when X86EMUL_UNRECOGNIZED
is returned by the emulator instead of just crash the domain.

Signed-off-by: Petre Pircalabu <ppircalabu@bitdefender.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>