VM_INJECT_EXCEPTION ioctl. However it morphed into other uses like keeping
track pending exceptions for a vcpu. This in turn causes confusion because
some fields in 'struct vm_exception' like 'vcpuid' make sense only in the
ioctl context. It also makes it harder to add or remove structure fields.
Fix this by using 'struct vm_exception' only to communicate information
from userspace to vmm.ko when injecting an exception.
Also, add a field 'restart_instruction' to 'struct vm_exception'. This
field is set to '1' for exceptions where the faulting instruction is
restarted after the exception is handled.
MFC after: 1 week
c9c75df48c